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Printed on 6/29/2026
For informational purposes only. This is not medical advice.
The Systemic Inflammatory Response Syndrome (SIRS) criteria were defined in 1992 as a set of four clinical findings that indicate a generalized inflammatory process. SIRS is present when two or more criteria are met: temperature >38°C or <36°C, heart rate >90 bpm, respiratory rate >20 or PaCO₂ <32 mmHg, and WBC >12,000 or <4,000 or >10% bands. While Sepsis-3 (2016) moved to SOFA-based definitions, SIRS criteria remain widely referenced and used in many clinical settings for early identification of inflammatory states. For Sepsis-3 diagnosis, use [qSOFA Score](/tools/qsofa) (bedside) and [SOFA Score](/tools/sofa-score) (full). Assess severity with [APACHE II](/tools/apache-ii). Track organ perfusion with [MAP Calculator](/tools/map-calculator). Pneumonia is the most common cause of sepsis — assess with [CURB-65](/tools/curb-65).
Formula: SIRS = sum of 4 criteria (each 0 or 1). SIRS positive ≥ 2.
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Evaluate four criteria: (1) Temperature: >38°C or <36°C. (2) Heart rate: >90 bpm. (3) Respiratory rate: >20 breaths/min OR PaCO₂ <32 mmHg. (4) WBC: >12,000/mm³ or <4,000/mm³ or >10% immature band forms. Each criterion is binary. SIRS can be assessed with temperature, HR, and RR before WBC is available.
SIRS is present if 2 or more of the 4 criteria are met. The number of SIRS criteria met (2, 3, or 4) provides additional prognostic value — more criteria generally indicate more severe systemic inflammation. However, even 4/4 SIRS criteria does not establish sepsis without a suspected or confirmed infection source.
SIRS + suspected infection: initiate sepsis workup (blood cultures, lactate, CBC/CMP, antibiotics) and calculate [qSOFA](/tools/qsofa) and [SOFA Score](/tools/sofa-score) for Sepsis-3 organ dysfunction assessment. SIRS without infection: evaluate for non-infectious causes (trauma, burns, pancreatitis, MI, PE, autoimmune). For CMS SEP-1 reporting, document SIRS recognition time as the sepsis bundle clock start.
Quality officers, hospitalists, ED physicians
The CMS SEP-1 quality measure still uses SIRS criteria + infection as the bundle trigger for regulatory reporting, despite Sepsis-3 replacing SIRS for clinical diagnosis. Hospitals must identify SIRS-based sepsis for CMS documentation. Track time of SIRS recognition as the 'sepsis clock' for SEP-1 compliance even while using qSOFA/SOFA clinically.
Emergency physicians, ward nurses, triage staff
Despite being replaced by Sepsis-3 for clinical diagnosis, SIRS retains approximately 90% sensitivity for bacteremia. SIRS + suspected infection should prompt blood cultures, lactate, and antibiotic consideration. Many hospital EHR-based sepsis alert systems still use SIRS as the trigger. Use alongside [qSOFA](/tools/qsofa) for dual-protocol approaches.
Gastroenterologists, general surgeons, hospitalists
SIRS presence in acute pancreatitis predicts severity: SIRS in the first 48 hours correlates with pancreatic necrosis and organ failure (Banks et al., revised Atlanta Classification 2012). Persistent SIRS (>48 hours) is the strongest predictor of severe acute pancreatitis requiring ICU-level care. Early aggressive fluid resuscitation in SIRS-positive pancreatitis improves outcomes.
Surgeons, post-operative nursing, hospitalists
SIRS is nearly universal in the first 24–48 hours after major surgery. The clinical challenge is distinguishing post-operative physiologic SIRS from early surgical site infection, anastomotic leak, or pneumonia. Serial SIRS assessment beyond post-operative day 2 is more clinically meaningful than early post-op SIRS.
Trauma surgeons, burn centers, ICU teams
Major trauma and extensive burns reliably trigger SIRS through non-infectious mechanisms (cytokine storm, tissue necrosis, reperfusion injury). Differentiating SIRS from developing infection requires serial clinical assessment, cultures, and procalcitonin. SIRS scores in trauma correlate with injury severity and predict ICU length of stay and organ dysfunction.
Clinical researchers, medical educators
An enormous body of sepsis literature uses SIRS-based definitions (pre-2016). Understanding SIRS criteria is essential for interpreting historical sepsis trials (PROWESS, CORTICUS, ProCESS, ARISE). SIRS-defined 'sepsis' in older studies includes a broader population than Sepsis-3 SOFA-defined sepsis. Apply appropriate interpretation when translating research findings to practice.
The Sepsis-3 task force abandoned SIRS as the sepsis definition due to its poor specificity (~50%). Sepsis-3 defines sepsis as suspected infection + SOFA ≥2. Clinically, use [qSOFA](/tools/qsofa) for bedside screening and [SOFA Score](/tools/sofa-score) for formal organ dysfunction quantification. Know SIRS for regulatory compliance and historical context.
CMS SEP-1 uses SIRS + infection as its trigger, despite Sepsis-3 replacing this clinically. Hospitals must document SIRS-based sepsis recognition for CMS compliance even when following Sepsis-3 clinically. Implement dual-protocol documentation: SIRS-based for CMS, qSOFA/SOFA-based for clinical practice.
In acute pancreatitis, transient SIRS (<48h) indicates mild-moderate disease; persistent SIRS (>48h) strongly predicts necrotizing pancreatitis and organ failure. The revised Atlanta Classification (2012) incorporates organ failure to define severe acute pancreatitis. Early aggressive fluid resuscitation (250–500 mL/h Lactated Ringer's) in SIRS-positive pancreatitis improves outcomes.
Immature neutrophils (bands) >10% indicate early bone marrow release under infectious stress. This is more specific for infection than total WBC elevation alone. Many automated CBC analyzers may not reliably count bands — manual differential may be needed. Bands >10% add meaningful specificity to the WBC criterion.
SIRS ≥2 criteria has approximately 90% sensitivity for bacteremia. A patient who does NOT meet SIRS criteria is unlikely to have bacteremia. However, 50% specificity means half of SIRS-positive patients don't have infection. Use SIRS to cast a wide net, then use clinical judgment and further workup to narrow the differential.
SIRS occurs with: MI, PE, trauma, burns, major surgery, pancreatitis, autoimmune disease, adrenal insufficiency, thyroid storm, heat stroke, and severe anemia. When SIRS is present without an obvious infection source, consider these diagnoses before reflexively starting antibiotics.
SIRS temperature criterion: >38°C (fever) OR <36°C (hypothermia). Hypothermia in sepsis is ominous — it may indicate overwhelming infection, gram-negative bacteremia, or immunosuppression. Hypothermic SIRS patients should be treated with the same urgency as febrile patients, if not more so.
The WBC criterion is positive if total WBC >12,000, <4,000, OR bands >10% regardless of total WBC. A patient with WBC 8,000 but 15% bands meets the WBC criterion. Always review the WBC differential when evaluating SIRS.
SIRS criteria defined by the ACCP/SCCM Consensus Conference (Bone et al., Chest 1992). SIRS as sepsis definition replaced by Sepsis-3 (Singer et al., JAMA 2016) based on poor specificity of SIRS for predicting infection-related organ dysfunction. CMS/TJC SEP-1 measure still uses SIRS as part of the trigger (Dellinger, Crit Care Med 2014 reporting infrastructure). SIRS sensitivity for bacteremia ~90%, specificity ~50%. SIRS in pancreatitis severity: Banks and Freeman (Am J Gastroenterol 2006 Atlanta Criteria revision).
Your result indicates whether the Systemic Inflammatory Response Syndrome (SIRS) criteria are met. Meeting two or more of the four criteria (abnormal temperature, tachycardia, tachypnea or low PaCO2, abnormal WBC) defines SIRS-positive status. A SIRS-positive result indicates that the body is mounting a systemic inflammatory response, which may be due to infection (sepsis), trauma, burns, pancreatitis, surgery, or other inflammatory conditions.
A SIRS-negative result (0–1 criteria met) suggests the patient does not currently display a generalized inflammatory response, though this does not rule out localized infection or early systemic disease. Serial reassessment is important because SIRS status can change rapidly as the clinical picture evolves.
Use the SIRS criteria as a bedside screening tool for early identification of systemic inflammation in acutely ill patients. It is most commonly applied in the emergency department, surgical settings, and inpatient wards when evaluating patients with suspected infection, post-operative fever, trauma, or other conditions that may trigger a systemic inflammatory response.
Although the Sepsis-3 definition (2016) moved toward SOFA-based criteria for defining sepsis, SIRS criteria remain valuable for initial screening, particularly in settings where laboratory values for SOFA are not immediately available. Many hospitals still use SIRS-based screening protocols as part of sepsis alert systems. The criteria are also widely used in clinical research and as inclusion criteria for clinical trials.
SIRS criteria are highly sensitive but poorly specific for infection. Up to 50% of hospitalized patients — particularly post-surgical patients, trauma patients, and those in the ICU — may meet SIRS criteria without having an infection. This high false-positive rate was a major reason the Sepsis-3 task force moved to SOFA-based definitions for sepsis.
Conversely, some patients with serious infections (particularly elderly or immunocompromised patients) may not mount a SIRS response, leading to false negatives. The criteria also do not differentiate between infectious and non-infectious causes of inflammation. For sepsis-specific screening, qSOFA or the full SOFA score may provide better specificity. SIRS criteria should always be interpreted alongside clinical context, not used as a standalone diagnostic tool.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
April 21, 2026 · trust-baseline
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