Medical Glossary

Acromegaly is a rare, slowly progressive endocrine disorder caused by chronic hypersecretion of growth hormone (GH) after fusion of the epiphyseal growth plates in adulthood (before epiphyseal fusion, excess GH causes gigantism). In approximately 95% of cases, the cause is a GH-secreting pituitary adenoma (somatotroph adenoma). GH stimulates the liver to produce insulin-like growth factor 1 (IGF-1), which mediates most of GH's effects and has a longer half-life, making IGF-1 the preferred screening and monitoring marker. Symptoms develop insidiously over years, often with a delay of 8-10 years before diagnosis. Somatic changes include enlargement of the hands, feet, and skull; coarsening of facial features (frontal bossing, jaw prognathism, widened nose); skin thickening; and hyperhidrosis. Systemic complications are the primary determinants of mortality and morbidity: cardiovascular disease (biventricular hypertrophy, hypertension, heart failure—the leading cause of premature death), diabetes mellitus (GH is insulin-antagonistic; impaired glucose tolerance in 30-50%, overt diabetes in 20-30%), sleep apnea (in 50-80%), colon polyps and increased colorectal cancer risk, joint disease (osteoarthritis), and carpal tunnel syndrome. Compression of local structures by the pituitary tumor can cause headaches, bitemporal hemianopia, and hypopituitarism. Diagnosis: elevated age-matched IGF-1 and failure to suppress GH below 1 ng/mL during a 75g oral glucose tolerance test. Treatment: transsphenoidal adenomectomy for eligible patients; somatostatin analogs (octreotide, lanreotide) for residual or recurrent disease; pegvisomant (GH receptor antagonist) for refractory cases; radiation for treatment-resistant tumors.

Acute kidney injury (AKI), previously called acute renal failure, is a sudden decrease in kidney function occurring over hours to days, characterized by rising serum creatinine, reduced urine output (oliguria), or both, resulting in accumulation of waste products and inability to maintain fluid and electrolyte homeostasis. According to the 2012 KDIGO (Kidney Disease: Improving Global Outcomes) criteria, AKI is diagnosed by any one of three criteria: an absolute increase in serum creatinine of at least 0.3 mg/dL (26.5 µmol/L) within 48 hours, a 50% increase in serum creatinine from baseline within 7 days, or urine volume less than 0.5 mL/kg/hour for at least 6 hours. Severity is staged 1 through 3 based on magnitude of creatinine rise or degree of oliguria, with stage 3 representing the most severe (creatinine increased to >3 times baseline or >4.0 mg/dL, urine output <0.3 mL/kg/hour for ≥24 hours, anuria for ≥12 hours, or initiation of renal replacement therapy). Patients with both oliguria and azotemia, or in whom these impairments persist, are more likely to have worse disease and outcomes. AKI causes are traditionally categorized into three types: prerenal (most common, approximately 60-70% of cases) results from reduced blood flow to the kidneys without direct kidney damage, due to hypovolemia (dehydration, bleeding, third-spacing), decreased effective circulating volume (heart failure, cirrhosis, sepsis), or renal artery obstruction; intrinsic renal or intrarenal (25-40% of cases) involves direct damage to kidney structures, most commonly acute tubular necrosis (ATN) from ischemia or nephrotoxins (aminoglycosides, NSAIDs, contrast dye, cisplatin), but also acute interstitial nephritis (drug hypersensitivity), glomerulonephritis, or vascular injury; and postrenal (5-10% of cases) results from obstruction of urine outflow, including bilateral ureteral obstruction (kidney stones, retroperitoneal fibrosis, malignancy) or bladder outlet obstruction (benign prostatic hyperplasia, urethral stricture, neurogenic bladder). Distinguishing prerenal from intrinsic AKI is clinically important because prerenal AKI is typically reversible with volume resuscitation, while ATN often requires supportive care and time for tubular regeneration. The fractional excretion of sodium (FENa) helps differentiate: FENa <1% suggests prerenal azotemia (kidneys avidly reabsorb sodium to conserve volume), while FENa >2% suggests intrinsic kidney disease like ATN (damaged tubules cannot reabsorb sodium effectively). Complications of AKI include volume overload and pulmonary edema, hyperkalemia (potentially causing life-threatening arrhythmias), metabolic acidosis, uremia (causing nausea, confusion, pericarditis), and electrolyte disturbances. Management focuses on identifying and treating the underlying cause (volume resuscitation for prerenal causes, stopping nephrotoxic drugs, relieving obstruction for postrenal causes), avoiding additional kidney injury (dose-adjust medications, avoid nephrotoxins, maintain adequate perfusion), carefully managing fluids and electrolytes, and initiating renal replacement therapy (dialysis) for life-threatening complications including refractory hyperkalemia, severe metabolic acidosis, uremic complications (pericarditis, encephalopathy), or volume overload unresponsive to diuretics. Many patients with AKI recover kidney function, though recovery time varies from days to weeks depending on severity and cause. However, AKI is associated with increased risk of developing chronic kidney disease and progression to end-stage renal disease, even after apparent recovery.

ARDS is a severe, life-threatening form of respiratory failure characterized by widespread inflammation in the lungs, leading to alveolar flooding, impaired gas exchange, and low lung compliance. The Berlin Definition (2012) classifies ARDS by the PaO2/FiO2 (P/F) ratio measured with PEEP of at least 5 cmH2O: mild (P/F 200-300 mmHg), moderate (P/F 100-200 mmHg), and severe (P/F below 100 mmHg). ARDS onset must occur within 1 week of a known clinical insult, bilateral opacities must be present on chest imaging, and respiratory failure must not be fully explained by cardiac failure or fluid overload. Common causes include sepsis (most common, approximately 40% of ARDS cases), aspiration pneumonitis, pneumonia, trauma, massive transfusion, and pancreatitis. Pathophysiologically, the exudative phase involves neutrophil-mediated endothelial and epithelial injury, increased vascular permeability, and flooding of alveoli with protein-rich edema. ICU mortality ranges from 35-40% for severe ARDS. The cornerstone of management is lung-protective ventilation: low tidal volumes (6 mL/kg ideal body weight), plateau pressure below 30 cmH2O, and PEEP titration to maintain alveolar recruitment. Prone positioning for 16 or more hours per day reduces mortality in moderate-severe ARDS. Neuromuscular blockade, dexamethasone, and conservative fluid strategy provide additional benefit in select patients.

Damage to the kidney tubules causing acute kidney injury. Usually results from prolonged ischemia (low blood flow) or nephrotoxins (contrast dye, certain medications). Characterized by FENa >2% and muddy brown casts in urine.

Adrenal insufficiency (AI) is a condition in which the adrenal glands produce insufficient cortisol and, in primary forms, also aldosterone, resulting in life-threatening if untreated. Primary adrenal insufficiency (Addison's disease) results from destruction of the adrenal cortex itself; in developed countries, autoimmune adrenalitis is the most common cause (with anti-21-hydroxylase antibodies serving as diagnostic markers), while tuberculosis remains the leading cause globally. Secondary AI results from pituitary or hypothalamic disorders reducing ACTH stimulation; tertiary AI results from prolonged exogenous glucocorticoid use suppressing the HPA axis (the most common cause worldwide, affecting any patient using more than 20 mg prednisone equivalent for over 3 weeks). Clinical features of chronic AI: fatigue, weight loss, anorexia, nausea, myalgias, salt craving, postural hypotension, and in primary AI only—hyperpigmentation (from elevated ACTH/MSH) and hyponatremia with hyperkalemia (from aldosterone deficiency). Adrenal crisis is a life-threatening emergency precipitated by physiological stress (illness, surgery, trauma) in a patient with unrecognized or undertreated AI, manifesting as severe hypotension, vomiting, abdominal pain, altered consciousness, and severe hyponatremia; immediate IV hydrocortisone (100 mg bolus) is life-saving. Diagnosis uses morning cortisol (below 3 mcg/dL strongly suggests AI), ACTH stimulation test (250 mcg cosyntropin, peak cortisol below 18-20 mcg/dL), and plasma ACTH to distinguish primary (elevated) from secondary/tertiary (low/normal). Treatment: hydrocortisone replacement (15-20 mg/day split doses, mimicking diurnal cortisol rhythm), fludrocortisone for primary AI, and mandatory stress-dosing (double to triple usual dose) during illness or surgery. Patients should carry medical alert identification and emergency hydrocortisone injection.

Albumin is the most abundant protein in human blood plasma, accounting for approximately 50-60% of total plasma protein, and is synthesized exclusively by the liver at a rate of about 10-15 grams per day. Normal serum albumin levels range from 3.5 to 5.0 g/dL (35-50 g/L). Albumin serves multiple critical functions: it maintains oncotic pressure (the osmotic pressure exerted by proteins that keeps fluid in the vascular space rather than leaking into tissues), transports various substances including hormones, fatty acids, bilirubin, calcium, and many medications (highly protein-bound drugs like warfarin and phenytoin bind primarily to albumin), provides nutritional reserves, and has antioxidant and anti-inflammatory properties. Low albumin (hypoalbuminemia, <3.5 g/dL) can result from decreased synthesis (chronic liver disease, malnutrition, inflammation), increased loss (nephrotic syndrome with urinary protein losses >3.5 g/day, protein-losing enteropathy, severe burns, large wounds), increased degradation, or dilution (fluid overload, pregnancy). Hypoalbuminemia has significant clinical consequences: reduced oncotic pressure leads to edema (swelling) and potentially ascites (abdominal fluid accumulation); altered drug pharmacokinetics occur because medications normally bound to albumin circulate in higher free concentrations, potentially causing toxicity at usual doses; and hypoalbuminemia is a strong predictor of poor outcomes—low albumin is associated with increased mortality, longer hospital stays, and higher complication rates across numerous conditions. Severe hypoalbuminemia (<2.5 g/dL) causes significant peripheral edema, ascites, and potentially pulmonary edema or pleural effusions as fluid shifts from the vascular space into tissues. Albumin levels are incorporated into several prognostic scoring systems: the Child-Pugh score for cirrhosis severity includes albumin as one of five criteria (points assigned for albumin <3.5 g/dL, with additional points if <2.8 g/dL), and the serum-ascites albumin gradient (SAAG, calculated as serum albumin minus ascitic fluid albumin) distinguishes portal hypertension-related ascites (SAAG ≥1.1 g/dL) from other causes (SAAG <1.1 g/dL). Because albumin binds approximately 40% of serum calcium, total calcium measurements can be misleadingly low in patients with hypoalbuminemia; corrected calcium calculations adjust for this by adding 0.8 mg/dL to the total calcium for each 1 g/dL the albumin is below 4.0 g/dL. Albumin has a relatively long half-life of about 20 days, so levels change slowly; this makes albumin useful for assessing chronic nutritional status or liver synthetic function but less useful for acute changes. Treatment of hypoalbuminemia focuses on addressing the underlying cause (improving nutrition, treating liver disease, reducing proteinuria in kidney disease) rather than albumin infusions, which provide only temporary benefit and are generally reserved for specific situations like large-volume paracentesis, hepatorenal syndrome, or spontaneous bacterial peritonitis treatment.

Alcohol use disorder is a chronic relapsing condition characterized by compulsive alcohol use, loss of control over intake, and negative emotional states when not drinking. DSM-5 defines AUD based on meeting 2 or more of 11 criteria within a 12-month period, including drinking more than intended, unsuccessful attempts to cut down, cravings, tolerance, withdrawal, and continued use despite problems. Severity is categorized as mild (2-3 criteria), moderate (4-5 criteria), or severe (6+ criteria). Approximately 14.5 million American adults have AUD, making it one of the most prevalent psychiatric conditions. The AUDIT (Alcohol Use Disorders Identification Test) screens across a spectrum from hazardous drinking to dependence; the CAGE questionnaire quickly screens for established alcohol problems. Alcohol withdrawal can be life-threatening (seizures, delirium tremens) and requires medical management. Evidence-based treatments include motivational interviewing, cognitive behavioral therapy, and medications (naltrexone, acamprosate, disulfiram). Early intervention during hazardous use can prevent progression to dependence.

The difference between oxygen in the alveoli (calculated) and oxygen in arterial blood (measured). A widened A-a gradient indicates a problem with oxygen transfer in the lungs, such as pulmonary embolism, pneumonia, or ARDS.

The Amniotic Fluid Index (AFI) is an ultrasound-based measurement used to quantify amniotic fluid volume during pregnancy. The technique divides the uterus into four quadrants and measures the deepest pocket of amniotic fluid in each quadrant; these four measurements are summed to calculate the AFI. Normal AFI values range from 5-25 cm, with oligohydramnios (too little fluid) defined as AFI <5 cm, and polyhydramnios (too much fluid) defined as AFI >25 cm. Amniotic fluid serves critical functions including cushioning the fetus from trauma, allowing fetal movement and musculoskeletal development, maintaining temperature, facilitating lung development, and preventing umbilical cord compression. AFI is assessed during routine third-trimester ultrasounds and antepartum fetal surveillance. Alternative assessment methods include measuring the single deepest vertical pocket (normal 2-8 cm) or subjective assessment. Abnormal amniotic fluid volumes signal potential problems: oligohydramnios may indicate placental insufficiency, fetal growth restriction, ruptured membranes, or fetal genitourinary abnormalities, while polyhydramnios may suggest maternal diabetes, fetal anomalies (particularly gastrointestinal or neurologic), or twin-to-twin transfusion syndrome. Management depends on the underlying cause and severity, ranging from increased surveillance to delivery if fetal well-being is compromised.

Anhedonia is the diminished ability to experience pleasure or interest in activities that were previously enjoyable. It is one of two cardinal symptoms required for major depression diagnosis (along with depressed mood) and represents a core feature of melancholic depression. Anhedonia manifests as loss of interest in hobbies, social activities, food, sex, and other previously rewarding experiences. Patients often describe feeling 'emotionally flat' or unable to enjoy anything. The PHQ-9's first question specifically assesses anhedonia ('Little interest or pleasure in doing things'). Beyond depression, anhedonia occurs in schizophrenia, Parkinson's disease, substance use disorders during withdrawal, and as a negative symptom of chronic illness. Neurobiologically, anhedonia is linked to dysfunction in dopamine reward pathways, particularly the mesolimbic system. Treatment-resistant anhedonia is a clinical challenge; some antidepressants (bupropion, MAOIs) may be more effective than others for this symptom. Behavioral activation therapy specifically targets anhedonia by gradually reintroducing pleasurable activities.

The anion gap is a calculated value derived from standard electrolyte panels that represents the difference between measured cations (positively charged ions) and measured anions (negatively charged ions) in blood serum. The principle of electroneutrality requires that total positive and negative charges in blood be equal, but routine laboratory testing measures only some of these ions. The anion gap accounts for unmeasured anions including albumin, phosphate, sulfate, and organic acids. The calculation is typically anion gap = (Na+) − (Cl− + HCO3−), though potassium can be included as anion gap = (Na+ + K+) − (Cl− + HCO3−); potassium is often omitted given its minimal contribution to the gap. Normal anion gap ranges from 6 to 12 mEq/L (or 12-16 mEq/L if potassium is included), with most laboratories using 8-12 mEq/L as the reference range. The anion gap is primarily used to classify metabolic acidosis into two categories: high anion gap metabolic acidosis (HAGMA) and normal anion gap (non-anion gap) metabolic acidosis. In high anion gap metabolic acidosis, abnormal or excess acids accumulate in the blood—these unmeasured anions (lactate, ketones, toxic metabolites) increase the anion gap, typically to values exceeding 12-16 mEq/L. The classic mnemonic MUDPILES helps remember common causes of high anion gap metabolic acidosis: Methanol ingestion, Uremia (kidney failure with accumulated organic acids), Diabetic ketoacidosis (and alcoholic or starvation ketoacidosis), Propylene glycol, Isoniazid and Iron toxicity, Lactic acidosis (from tissue hypoperfusion, sepsis, seizures, or metformin), Ethylene glycol (antifreeze) ingestion, and Salicylate (aspirin) toxicity. Lactic acidosis and ketoacidosis are the most common causes in clinical practice. Normal anion gap metabolic acidosis (also called non-anion gap or hyperchloremic acidosis) occurs when bicarbonate is lost from the body or when the kidneys fail to excrete hydrogen ions, but this is accompanied by retention of chloride to maintain electroneutrality—thus the anion gap remains normal. Causes include diarrhea (gastrointestinal bicarbonate loss), renal tubular acidosis, carbonic anhydrase inhibitors like acetazolamide, early kidney disease, and rapid IV saline administration. The anion gap can be affected by changes in albumin concentration—since albumin is a major unmeasured anion, hypoalbuminemia decreases the anion gap by approximately 2.5 mEq/L for each 1 g/dL decrease in albumin below 4 g/dL. Therefore, in patients with low albumin, the anion gap should be corrected: corrected anion gap = measured anion gap + 2.5 × (4 − measured albumin). This correction is important because patients with hypoalbuminemia may have a high anion gap acidosis that appears normal on uncorrected calculations. Evaluation of an elevated anion gap should include measuring serum lactate, ketones (beta-hydroxybutyrate), creatinine, and consideration of toxic alcohol ingestion (methanol, ethylene glycol) with measurement of serum osmolality to calculate the osmolar gap.

Ankylosing spondylitis is a chronic inflammatory arthritis primarily affecting the sacroiliac joints and spine, belonging to the family of spondyloarthropathies. It is strongly associated with the HLA-B27 antigen, present in 85-95% of patients with AS compared with 6-8% of the general population. AS predominantly affects young men (male-to-female ratio approximately 3:1), with typical onset between ages 20-40 years. The hallmark symptom is inflammatory back pain—insidious onset, age under 45, morning stiffness lasting more than 30 minutes, improvement with exercise (not rest), and nocturnal awakening. Progressive inflammation leads to new bone formation (syndesmophytes) and eventual spinal fusion, creating the classic "bamboo spine" appearance on X-ray. Extra-articular manifestations are common: acute anterior uveitis (25-40% of patients; recurrent, painful, photophobic eye inflammation), inflammatory bowel disease association (Crohn's disease, ulcerative colitis), psoriasis, and cardiac conduction abnormalities. The Assessment of SpondyloArthritis International Society (ASAS) criteria distinguish axial spondyloarthritis (with or without radiographic sacroiliitis) from peripheral spondyloarthritis. MRI of the sacroiliac joints detects active inflammation before X-ray changes appear, enabling earlier diagnosis of non-radiographic axial SpA. Inflammatory markers (CRP, ESR) are elevated in 50-70% of patients. Treatment: NSAIDs remain first-line and are highly effective—sustained NSAID use may retard radiographic progression. TNF inhibitors (adalimumab, etanercept, infliximab, certolizumab, golimumab) are the gold-standard biologic therapy, dramatically improving symptoms and functional outcomes. IL-17A inhibitors (secukinumab, ixekizumab) are effective alternatives, particularly for peripheral joint disease and psoriasis. Physical therapy and posture exercises are essential to maintain spinal mobility and prevent deformity. Disease monitoring uses the BASDAI (Bath AS Disease Activity Index) and ASDAS scores.

Antibiotic stewardship refers to coordinated programs and strategies to optimize antibiotic use in clinical practice—selecting the right antibiotic, at the right dose, for the right duration, targeting the right pathogen—with the goals of improving patient outcomes, reducing antibiotic-associated adverse effects, and curbing the development and spread of antibiotic resistance. Antimicrobial resistance (AMR) is one of the most significant public health threats globally, responsible for approximately 700,000 deaths annually worldwide (projected to exceed 10 million by 2050 if unaddressed). The overuse and misuse of antibiotics (including prescribing for viral infections, using broad-spectrum agents when narrow-spectrum would suffice, and unnecessarily long treatment durations) are the primary drivers of resistance emergence. Key stewardship strategies include: prospective audit and feedback (pharmacist or infectious disease specialist reviews antibiotic prescriptions and provides evidence-based recommendations); prior authorization (requiring approval for broad-spectrum or high-risk antibiotics before dispensing); clinical guidelines and order sets; culture-directed de-escalation (switching from empiric broad-spectrum therapy to targeted narrow-spectrum antibiotics when culture results return—'when in doubt, de-escalate'); duration optimization (clinical decision support for antibiotic duration based on infection type); diagnostic stewardship (improving test ordering and result interpretation to reduce inappropriate testing that leads to overtreatment); and dose optimization (pharmacokinetic/pharmacodynamic principles for aminoglycosides and vancomycin dosing). The Centor and McIsaac scores guide antibiotic prescribing for pharyngitis (avoiding antibiotics for viral causes), significantly reducing unnecessary prescribing. Sepsis protocols ensure timely antibiotic administration when needed, balancing the harm of delay against the harm of unnecessary treatment.

Treatment with medications that prevent blood clots from forming or growing. Common anticoagulants include warfarin and direct oral anticoagulants (DOACs) like apixaban and rivaroxaban. Used to prevent stroke in AFib and treat/prevent blood clots.

Antinuclear antibodies are autoantibodies directed against components of the cell nucleus (DNA, histones, and various nuclear proteins). ANA testing by indirect immunofluorescence (IIF) on HEp-2 cells is the standard screening test for systemic autoimmune rheumatic diseases (SARDs). The ANA titer and pattern are reported together: the titer indicates the serum dilution at which the test remains positive (higher titers are more clinically significant); the pattern (homogeneous, speckled, nucleolar, centromere, etc.) provides clues to specific autoantibody types. An ANA titer of 1:40 or above is considered positive by most laboratories, though 1:80 or 1:160 is often used as a clinically meaningful threshold to reduce false positives. ANA positivity is present in over 99% of SLE patients (making it an excellent screening test), 95% of scleroderma, 70% of Sjogren's syndrome, 40% of primary biliary cholangitis, and 25-30% of rheumatoid arthritis. However, a positive ANA alone is not diagnostic of any disease—it occurs in 13-15% of healthy adults (particularly women and older individuals) and in many non-rheumatic conditions (viral infections, thyroid disease, malignancy). When the ANA is positive, specific extractable nuclear antigen (ENA) panel testing guides diagnosis: anti-dsDNA and anti-Smith are highly specific for SLE; anti-Ro/SSA and anti-La/SSB for Sjogren's and neonatal lupus; anti-Scl-70 (topoisomerase I) for diffuse systemic sclerosis; anti-centromere for limited systemic sclerosis (CREST); anti-Jo-1 for polymyositis/dermatomyositis with ILD; anti-U1RNP for mixed connective tissue disease. The clinical probability of SLE before testing significantly impacts the positive predictive value of ANA testing—in a low-risk patient with only fatigue and positive ANA 1:80, SLE is unlikely; in a patient with malar rash, arthritis, and nephritis, a positive ANA 1:320 is highly informative.

A quick assessment of newborn health performed at 1 and 5 minutes after birth. Evaluates Appearance (skin color), Pulse, Grimace (reflex irritability), Activity (muscle tone), and Respiration. Scores range from 0-10; scores below 7 may indicate need for medical attention.

The partial pressure of oxygen dissolved in arterial blood, measured by arterial blood gas (ABG). Normal is 80-100 mmHg at sea level. Directly measures oxygenation, unlike pulse oximetry which estimates it non-invasively.

Ascites is the pathological accumulation of fluid in the peritoneal cavity—the space between the two layers of the peritoneum that lines the abdominal organs. Cirrhosis of the liver is the most common cause of ascites, accounting for 80-90% of cases in developed countries. The development of ascites in cirrhotic patients marks the transition from compensated to decompensated cirrhosis and is associated with significantly reduced survival (approximately 50% two-year mortality without liver transplantation). The pathophysiology of cirrhotic ascites involves portal hypertension (increased pressure in the portal venous system due to scarred liver tissue obstructing blood flow), splanchnic vasodilation (widening of blood vessels in the intestinal circulation), activation of sodium-retaining hormones (renin-angiotensin-aldosterone system), and reduced albumin synthesis leading to decreased oncotic pressure. Other causes of ascites include heart failure (5-10% of cases), malignancy with peritoneal carcinomatosis (10%), tuberculosis, pancreatitis, and nephrotic syndrome. Symptoms of ascites include progressive abdominal distention and swelling, weight gain, shortness of breath (particularly when lying flat, as fluid compresses the diaphragm), early satiety, nausea, lower extremity edema, and reduced mobility. Physical examination may reveal bulging flanks, shifting dullness on percussion, and a fluid wave. Diagnosis is confirmed by abdominal ultrasound or CT scan. Diagnostic paracentesis (sampling ascitic fluid with a needle) should be performed in all new-onset ascites and whenever spontaneous bacterial peritonitis is suspected; fluid analysis includes cell count with differential, albumin (to calculate serum-ascites albumin gradient or SAAG), total protein, Gram stain, and culture. A SAAG ≥1.1 g/dL indicates portal hypertension as the cause, while SAAG <1.1 g/dL suggests other etiologies like malignancy or tuberculosis. Management of cirrhotic ascites follows a stepwise approach: the most important initial step is strict sodium restriction (limit to <2,000 mg daily), as excess sodium intake is the primary driver of fluid retention. For patients not responding to dietary sodium restriction alone, diuretic therapy is initiated with spironolactone (aldosterone antagonist) often combined with furosemide (loop diuretic), titrated to achieve gradual weight loss of 0.5 kg/day without peripheral edema or 1 kg/day with peripheral edema. Therapeutic large-volume paracentesis (removing 5+ liters) provides rapid symptomatic relief for tense ascites and can be repeated as needed. Refractory ascites (not responding to maximum medical therapy) may require serial large-volume paracentesis, indwelling peritoneal catheters, transjugular intrahepatic portosystemic shunt (TIPS), or liver transplantation evaluation.

Asthma is a chronic inflammatory disease of the airways characterized by variable and reversible airflow obstruction, airway hyperresponsiveness, and underlying inflammation. Unlike COPD, airflow obstruction in asthma is largely reversible—spontaneously or with bronchodilator therapy. The pathophysiology involves type 2 immune inflammation (eosinophilic in most cases) with mast cell activation, leading to bronchoconstriction, mucus hypersecretion, and airway wall remodeling over time. Symptoms include episodic wheezing, chest tightness, shortness of breath, and cough, classically worse at night and early morning and triggered by allergens, exercise, respiratory infections, cold air, smoke, and irritants. The Asthma Control Test (ACT) is a validated 5-item questionnaire that assesses asthma symptom control over the preceding 4 weeks, helping clinicians identify inadequately controlled asthma requiring step-up therapy. Diagnosis relies on demonstration of variable airflow limitation (reversible FEV1 reduction, peak flow variability, or bronchial hyperresponsiveness on methacholine challenge), as spirometry may be normal between episodes. The GINA (Global Initiative for Asthma) guidelines classify asthma by symptom control (well-controlled, partially controlled, uncontrolled) and treatment step rather than severity. Treatment follows a stepwise approach: reliever inhalers (short-acting beta-2 agonists) for acute symptoms, with controller therapy (inhaled corticosteroids as backbone, with added LABAs, leukotriene receptor antagonists, or biologics for severe eosinophilic or allergic asthma) based on control level.

Atherosclerosis is a progressive disease characterized by the buildup of plaque inside arteries, causing the vessel walls to thicken and harden over time. Plaque consists of deposits of fat, cholesterol, cellular waste products, calcium, and fibrin that accumulate in the inner lining of arterial walls. This process begins as early as childhood and typically progresses slowly over decades, though certain risk factors can accelerate its development. As plaque accumulates, arteries narrow and lose flexibility, limiting blood flow to vital organs and tissues. The greatest danger occurs when a plaque becomes unstable and ruptures, triggering blood clot formation that can suddenly block the artery completely or break off and travel to block blood vessels elsewhere in the body. Atherosclerosis is the underlying cause of most cardiovascular disease, including coronary artery disease (heart attack), cerebrovascular disease (stroke), peripheral artery disease (leg pain and claudication), and aortic aneurysms. The location of atherosclerotic plaques determines which complications may occur: plaques in coronary arteries can cause angina or heart attack, plaques in carotid arteries supplying the brain increase stroke risk, and plaques in arteries of the legs cause peripheral artery disease with symptoms of claudication (leg pain when walking). Risk factors for atherosclerosis include both modifiable and non-modifiable factors. Non-modifiable risk factors include age (men over 45, women over 55), family history of premature atherosclerosis, and genetic factors. Modifiable risk factors include dyslipidemia (high LDL cholesterol, low HDL cholesterol, elevated triglycerides), hypertension, diabetes and insulin resistance, cigarette smoking, obesity (particularly central adiposity), physical inactivity, unhealthy diet high in saturated fats and trans fats, chronic inflammation, and chronic kidney disease. Atherosclerosis is often asymptomatic until it becomes severe enough to significantly limit blood flow or causes an acute event like heart attack or stroke. Prevention and treatment focus on aggressive risk factor modification: managing blood pressure and cholesterol with lifestyle changes and medications (statins being a cornerstone of therapy), controlling diabetes, smoking cessation, regular physical activity, maintaining healthy weight, and adopting a heart-healthy diet rich in fruits, vegetables, whole grains, and omega-3 fatty acids while limiting saturated fats, trans fats, and sodium.

An irregular and often rapid heart rhythm where the heart's upper chambers (atria) beat chaotically. This can cause blood to pool and form clots, increasing stroke risk. Common symptoms include palpitations, shortness of breath, and fatigue.

Attention-deficit/hyperactivity disorder is a neurodevelopmental disorder characterized by persistent patterns of inattention and/or hyperactivity-impulsivity that interfere with functioning or development, with onset before age 12. ADHD affects approximately 5-7% of children and 2-5% of adults globally, making it the most prevalent neurodevelopmental disorder of childhood. Three presentations: predominantly inattentive (difficulty sustaining attention, easily distracted, forgetful, disorganized); predominantly hyperactive-impulsive (fidgeting, talking excessively, difficulty waiting turn, impulsive decisions); and combined presentation (most common). DSM-5 diagnosis requires 6 or more inattentive and/or hyperactive-impulsive symptoms in children (5 or more in adults 17+), present in two or more settings, causing functional impairment, and not better explained by another condition. ADHD is highly heritable (heritability ~75%) and involves dysregulation of dopaminergic and noradrenergic pathways in prefrontal cortex, affecting executive function, attention regulation, and impulse control. ADHD frequently co-occurs with learning disabilities, anxiety disorders, depression, oppositional defiant disorder, and conduct disorder. In adults, hyperactivity often diminishes but inattention, executive dysfunction, and emotional dysregulation persist, contributing to academic underachievement, occupational difficulties, and relationship problems. Treatment: stimulant medications are the most effective pharmacological treatment—methylphenidate (Ritalin, Concerta) and amphetamine salts (Adderall, Vyvanse); both enhance dopaminergic and noradrenergic neurotransmission. Non-stimulant alternatives: atomoxetine (norepinephrine reuptake inhibitor), guanfacine and clonidine (alpha-2 agonists), and bupropion. Behavioral interventions (parent management training, classroom accommodations, cognitive-behavioral therapy for adults) are recommended especially in children and as adjuncts in all ages. Multimodal treatment combining medication and behavioral therapy is optimal.

Autism spectrum disorder is a neurodevelopmental condition characterized by persistent deficits in social communication and interaction, and restricted, repetitive patterns of behavior, interests, or activities, with symptoms present in early childhood. ASD affects approximately 1 in 36 children (CDC 2023 estimate), representing a significant increase in prevalence over recent decades, attributable to broadened diagnostic criteria, increased awareness, and improved screening. The term "spectrum" reflects wide variation in severity, functional ability, and presentation. DSM-5 diagnostic criteria: (A) persistent deficits in social-emotional reciprocity, nonverbal communicative behaviors, and developing/maintaining relationships; AND (B) restricted, repetitive behaviors (stereotypies, insistence on sameness, highly restricted interests, hyper- or hyposensitivity to sensory input). Level 1 (requiring support), Level 2 (requiring substantial support), and Level 3 (requiring very substantial support) specify severity. Social (pragmatic) communication disorder (SCD) is distinguished by absent restrictive/repetitive behaviors. ASD is highly heritable (heritability 64-91%); no single gene accounts for most cases; hundreds of risk genes identified. Intellectual disability co-occurs in approximately 30-40%; epilepsy in 20-30%. Sensory processing differences are nearly universal. Co-occurring ADHD (50%), anxiety (40%), and depression are common. Diagnosis is clinical and multidisciplinary—no biomarkers; standardized tools (ADOS-2, ADI-R) inform evaluation. No medications treat core ASD symptoms; pharmacotherapy targets co-occurring conditions (stimulants for ADHD, SSRIs/SNRIs for anxiety, antipsychotics for severe irritability/aggression—aripiprazole and risperidone FDA-approved for ASD-related irritability). Evidence-based behavioral interventions: Applied Behavior Analysis (ABA), speech-language therapy, occupational therapy, and social skills training. Early intensive intervention significantly improves outcomes.

Bacteremia is the presence of viable bacteria in the bloodstream, detected by blood culture. It exists on a spectrum from transient bacteremia (brief, often clinically silent bacteremia following dental procedures, catheter insertion, or bowel preparation—usually cleared by the immune system in healthy hosts) to sustained or high-grade bacteremia (persistent bacterial presence indicating failure of clearance, typical of endovascular infection, severe sepsis, or immunocompromised states). Blood cultures are the gold standard for diagnosing bacteremia; at least 2 sets (each containing an aerobic and anaerobic bottle) drawn from separate venipuncture sites are recommended to distinguish true bacteremia from skin contaminant. True bacteremia is suggested by multiple positive cultures with the same organism, growth within 24 hours, and a virulent pathogen (Staphylococcus aureus, Streptococcus pneumoniae, Enterobacteriaceae, Pseudomonas). Contaminants are more often coagulase-negative staphylococci in a single culture set. Staphylococcus aureus bacteremia (SAB) deserves special mention: it always represents true infection, requires aggressive treatment (4-6 weeks of IV antibiotics for deep-seated infection), and should prompt evaluation for infective endocarditis (transesophageal echocardiography recommended if transthoracic echo is negative and clinical suspicion remains) and metastatic foci (vertebral osteomyelitis, septic arthritis, epidural abscess). Gram-negative bacteremia (E. coli from UTI, Klebsiella, Pseudomonas, Enterobacter) requires culture-directed antibiotic selection, particularly with the rising prevalence of multidrug-resistant organisms (MDROs) including carbapenem-resistant Enterobacterales (CRE). Blood culture turnaround time averages 12-48 hours; rapid diagnostic tests (MALDI-TOF, PCR panels) can accelerate identification of the organism and resistance patterns.

The number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, and cell production. Represents the minimum energy needed to keep your body functioning.

Bilirubin is a yellow-orange pigment formed from the breakdown of hemoglobin when red blood cells reach the end of their 120-day lifespan and are destroyed in the spleen and liver. Normal total bilirubin levels range from 0.1 to 1.2 mg/dL, with direct (conjugated) bilirubin comprising less than 0.3 mg/dL of the total. Bilirubin metabolism follows several steps: hemoglobin from destroyed red blood cells is converted to unconjugated (indirect) bilirubin, which is not water-soluble and travels in blood bound to albumin; the liver takes up unconjugated bilirubin and conjugates it with glucuronic acid to form conjugated (direct) bilirubin, which is water-soluble; conjugated bilirubin is excreted into bile and eventually reaches the intestine, where bacteria convert it to urobilinogen and stercobilin (which gives stool its brown color). Elevated bilirubin (hyperbilirubinemia) causes jaundice—a yellow discoloration of the skin, sclera (whites of the eyes), and mucous membranes that becomes clinically apparent when total bilirubin exceeds approximately 2.5-3.0 mg/dL. The pattern of bilirubin elevation helps identify the underlying problem: predominantly unconjugated (indirect) hyperbilirubinemia suggests increased red blood cell destruction (hemolytic anemia), impaired hepatic uptake (heart failure, portosystemic shunts), or decreased conjugation (Gilbert syndrome, Crigler-Najjar syndrome), while predominantly conjugated (direct) hyperbilirubinemia indicates impaired bile excretion from hepatocellular injury (viral hepatitis, medication toxicity, alcohol, cirrhosis), bile duct obstruction (gallstones, pancreatic cancer, strictures), or inherited disorders affecting bile excretion (Dubin-Johnson syndrome, Rotor syndrome). Very high bilirubin levels (>30 mg/dL) in newborns can cause kernicterus, a form of brain damage from bilirubin deposition in the basal ganglia, which is why neonatal jaundice is monitored closely and treated with phototherapy or exchange transfusion when indicated. Bilirubin is incorporated into important prognostic scoring systems: the MELD score (Model for End-Stage Liver Disease) uses total bilirubin along with creatinine and INR to predict mortality in patients with liver disease and prioritize liver transplant allocation, while the Child-Pugh score includes bilirubin as one of five criteria to assess cirrhosis severity (points assigned based on whether bilirubin is <2 mg/dL, 2-3 mg/dL, or >3 mg/dL). Evaluation of elevated bilirubin involves differentiating unconjugated from conjugated bilirubin, assessing liver enzymes (ALT, AST, alkaline phosphatase) to distinguish hepatocellular injury from cholestasis, and imaging (ultrasound or CT) to evaluate for bile duct dilation suggesting obstruction. Treatment depends on the underlying cause and may include treating hemolysis, removing offending medications, treating viral hepatitis, managing cirrhosis complications, or relieving bile duct obstruction through endoscopic procedures (ERCP with stone removal or stent placement) or surgery.

Bipolar disorder is a chronic mood disorder characterized by episodic disturbances of mood, energy, and functioning, cycling between (hypo)manic and depressive states. It affects approximately 2% of the global population and represents one of the top causes of disability worldwide. Bipolar I disorder: at least one manic episode (elevated or irritable mood plus increased energy for at least 7 days, requiring hospitalization or causing marked impairment; includes psychotic features in severe cases). Depressive episodes occur in most patients but are not required for diagnosis. Bipolar II disorder: at least one hypomanic episode (manic symptoms lasting at least 4 days, not requiring hospitalization, without psychosis) and at least one major depressive episode. Hypomania is often not recognized by patients. Cyclothymic disorder: chronic, fluctuating mood with hypomanic and depressive symptoms not meeting full criteria for over 2 years. Bipolar disorder is frequently misdiagnosed as unipolar depression (depressive phases predominate in total duration); misdiagnosis leads to antidepressant monotherapy, which can precipitate mania. Accurate diagnosis requires a detailed mood history and screening for hypomanic symptoms (MDQ—Mood Disorder Questionnaire). Course: episodic with often incomplete interepisodic recovery; rapid cycling (four or more episodes per year) indicates greater severity. Suicide risk: 15-20 times higher than general population; mixed episodes and depressive phases carry highest risk. Treatment: acute mania—lithium, valproate, and atypical antipsychotics (olanzapine, quetiapine, aripiprazole, risperidone) are first-line. Acute bipolar depression—quetiapine, lurasidone, lamotrigine, lithium. Maintenance—lithium (reduces suicide risk by 5-fold, only medication with proven anti-suicidal effect), valproate, lamotrigine (superior for depression prevention), or atypical antipsychotics. Psychotherapy (CBT, IPSRT, family-focused therapy) reduces relapse rates.

A scoring system used to predict whether labor induction will be successful. Evaluates cervical dilation, effacement, station, consistency, and position. Higher scores (≥8) indicate a favorable cervix more likely to result in successful vaginal delivery.

A blood test measuring the amount of nitrogen from urea, a waste product of protein metabolism. Elevated BUN can indicate kidney problems, dehydration, high protein intake, or gastrointestinal bleeding.

Body fat percentage represents the proportion of fat tissue relative to your total body weight, expressed as a percentage. Unlike BMI, which simply relates weight to height, body fat percentage directly measures the ratio of fat mass to lean mass (muscle, bone, organs, and water), providing a more accurate assessment of body composition and health risk. The body contains two types of fat: essential fat (necessary for vital functions like hormone production and temperature regulation) and storage fat (energy reserves in adipose tissue). Essential fat comprises approximately 2-5% in men and 10-13% in women, with women requiring higher percentages to support reproductive functions and hormonal balance. Healthy body fat ranges vary by sex and age, but generally fall between 8-19% for men and 21-33% for women according to most health organizations. Athletes may have lower percentages (6-13% for male athletes, 14-20% for female athletes), while percentages above 25% in men or 32% in women are typically considered elevated and associated with increased health risks. Extremely low body fat (below essential levels) can be dangerous, leading to hormonal imbalances, decreased immune function, and reproductive issues. Several methods can measure body fat percentage with varying accuracy: DEXA scans (most accurate, using dual-energy X-ray absorptiometry), bioelectrical impedance analysis or BIA (common in home scales, affected by hydration), skinfold calipers (inexpensive but technique-dependent), and the U.S. Navy method (uses body circumference measurements). Body fat percentage provides better health insights than weight or BMI alone because it distinguishes between muscle and fat—two people with identical BMIs can have vastly different body compositions and health profiles. Monitoring body fat percentage is particularly useful for athletes, those undergoing body recomposition, and anyone seeking to improve metabolic health rather than simply losing weight.