What is the CURB-65 score?

CURB-65 stands for Confusion, Urea (BUN), Respiratory rate, Blood pressure, and age ≥65. Each criterion present scores 1 point, for a maximum of 5. It was developed by the British Thoracic Society to assess pneumonia severity.

How does CURB-65 guide treatment?

Score 0–1: Low risk (~1.5% mortality) — consider outpatient treatment. Score 2: Moderate risk (~9% mortality) — consider short hospital stay or closely supervised outpatient. Score 3–5: High risk (15–40% mortality) — hospitalize, consider ICU for scores 4–5.

CRB-65 is a simplified version that omits the BUN lab value, making it usable in outpatient settings without blood tests. It uses only Confusion, Respiratory rate, Blood pressure, and age ≥65. A CRB-65 of 0 suggests low risk.

Which CURB-65 score usually needs hospital admission?

Scores 0-1 are often outpatient if clinically stable, score 2 usually warrants admission or very close observation, and scores 3-5 generally require hospital care with consideration of ICU at higher scores.

Are there limitations to CURB-65?

CURB-65 does not account for comorbidities, immune status, multilobar involvement, or other markers of severe illness (e.g., hypoxia, lactate). It should be used alongside clinical judgment, especially in younger patients where severe pneumonia may not be captured by age-based criteria.

Who developed CURB-65?

CURB-65 was developed by the British Thoracic Society and validated in studies by Lim et al. (Thorax 2003). It was derived from a large cohort of CAP patients in the UK and has since been validated internationally.

What are the mortality rates by score?

CURB-65 0: 0.6%, CURB-65 1: 2.7%, CURB-65 2: 6.8%, CURB-65 3: 14.0%, CURB-65 4: 27.8%, CURB-65 5: 57.0%. These are 30-day mortality rates from the original validation study.

Does CURB-65 include oxygen saturation?

No. CURB-65 does not include SpO2 or PaO2. Hypoxia (SpO2 <92% or PaO2 <60 mmHg) is an independent criterion for hospitalization and should be assessed separately. Some guidelines use CURB-65 plus oxygen saturation together.

Can CURB-65 be used in COVID-19 pneumonia?

CURB-65 was not specifically validated for COVID-19. Studies during the pandemic showed variable performance. COVID-specific severity scores (4C Mortality Score, NEWS2) may be more appropriate, though CURB-65 can still provide a general severity estimate.

What counts as low blood pressure?

Systolic BP < 90 mmHg OR diastolic BP ≤ 60 mmHg. Either criterion being met scores 1 point. This reflects hemodynamic compromise associated with severe infection.

What respiratory rate threshold is used?

Respiratory rate ≥ 30 breaths per minute. This indicates significant respiratory distress and increased work of breathing, associated with worse outcomes in pneumonia.

How is confusion assessed?

Confusion is defined as new disorientation to person, place, or time. The Abbreviated Mental Test Score (AMTS ≤8) or [Glasgow Coma Scale](/tools/glasgow-coma-scale) can also be used. Don't count chronic baseline confusion unless there is acute deterioration.

What BUN level is the threshold?

BUN > 19 mg/dL (or blood urea > 7 mmol/L). This reflects either dehydration, renal impairment, or high catabolic state — all associated with worse pneumonia outcomes.

Is CURB-65 used worldwide?

Yes. CURB-65 is endorsed by the British Thoracic Society, European Respiratory Society, and referenced in IDSA/ATS guidelines. It is widely used in Europe, Asia, and increasingly in North America alongside PSI.

What is the Pneumonia Severity Index (PSI)?

PSI (also called PORT score) is a more comprehensive 20-variable risk score that classifies patients into 5 risk classes. It is more accurate than CURB-65 but more complex to calculate. Both are valid tools for pneumonia severity assessment.

Online Medical Tools — CURB-65 Score

Printed on 8/14/2026

For informational purposes only. This is not medical advice.

Emergency

CURB-65 Score

CURB-65 is a clinical prediction rule for estimating mortality risk in community-acquired pneumonia (CAP). It helps clinicians decide whether a patient can be treated as an outpatient or requires hospital admission. The score evaluates five criteria: Confusion, BUN, Respiratory rate, Blood pressure, and age ≥65.

Formula: CURB-65 = Confusion(1) + BUN>19(1) + RR≥30(1) + BP low(1) + Age≥65(1)

Confusion (new disorientation in person, place, or time)

BUN > 19 mg/dL (> 7 mmol/L)

Respiratory Rate ≥ 30/min

Blood Pressure: SBP < 90 or DBP ≤ 60 mmHg

Age ≥ 65 years

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How It Works

Assess the five CURB-65 criteria

Evaluate confusion (new disorientation to person, place, or time), BUN > 19 mg/dL, respiratory rate ≥ 30/min, blood pressure (SBP < 90 or DBP ≤ 60), and age ≥ 65 years.

Calculate the total score

Each criterion present scores 1 point. The total score ranges from 0 to 5. Enter each finding into the calculator to generate the total.

Apply the disposition recommendation

Score 0–1: consider outpatient treatment. Score 2: consider short hospitalization or close outpatient follow-up. Score 3–5: hospitalize; scores 4–5 may warrant ICU consideration. For ICU patients, calculate [APACHE II](/tools/apache-ii) or [SOFA Score](/tools/sofa-score) for comprehensive severity assessment.

Who Uses the CURB-65 Score

Emergency Department Triage

Emergency physicians, triage nurses

Rapidly assess pneumonia severity to determine whether a patient can be safely discharged with oral antibiotics or requires hospital admission for IV therapy and monitoring.

Hospital Admission Decisions

Hospitalists, internal medicine

Provide objective evidence to support admission decisions when the clinical picture is ambiguous. A CURB-65 of 2+ provides justification for inpatient care.

Primary Care Evaluation

Family medicine, urgent care

Use CRB-65 (without BUN) in outpatient settings to identify patients who need emergency referral versus those safe for home treatment with close follow-up.

Quality Improvement

Hospital quality teams

Track pneumonia severity scores across patient populations to benchmark outcomes, identify overtriage or undertriage patterns, and improve care protocols.

Pandemic Surge Planning

Hospital administrators, public health

During respiratory illness outbreaks, CURB-65 helps allocate limited hospital beds to the sickest patients while safely discharging lower-risk individuals.

Clinical Documentation

All clinicians

Document objective severity assessment to support clinical decision-making, communicate with consulting services, and provide medicolegal documentation of disposition rationale.

Pro Tips

Use CRB-65 when labs aren't available

In outpatient or prehospital settings, use CRB-65 (omitting BUN). A CRB-65 of 0 identifies very low-risk patients; CRB-65 ≥1 warrants hospital evaluation.

CURB-65 underscores young severe pneumonia

A 40-year-old with severe pneumonia, hypoxia, and bilateral infiltrates may score only 1 (for elevated BUN or tachypnea). Age-based criteria mean younger patients can be undertriaged. Always consider hypoxia and imaging.

Combine with oxygen saturation

CURB-65 doesn't include SpO2 or PaO2. An SpO2 <92% on room air is itself an indication for hospitalization, regardless of the CURB-65 score. Use [A-a Gradient](/tools/aa-gradient) to assess oxygenation deficits and [ABG Interpreter](/tools/abg-interpreter) for acid-base status.

Consider comorbidities separately

CURB-65 doesn't account for COPD, heart failure, diabetes, or immunosuppression. Patients with significant comorbidities may need admission even with low CURB-65 scores. Assess cardiovascular risk with [ASCVD Risk Calculator](/tools/ascvd-risk) for patients with heart disease.

PSI is more comprehensive but complex

The Pneumonia Severity Index (PSI/PORT score) includes 20 variables and is more accurate but harder to calculate. CURB-65 is faster and preferred for bedside use; PSI may be better for research or detailed risk stratification.

Score 2 is the gray zone

Patients with CURB-65 of 2 have ~9% mortality and require careful clinical judgment. Consider social factors, ability to tolerate oral medications, follow-up access, and oxygen requirements.

Confusion assessment matters

Use a standardized assessment (Abbreviated Mental Test Score ≤8, or new disorientation to person/place/time, or [Glasgow Coma Scale](/tools/glasgow-coma-scale) if severely altered). Don't count chronic baseline confusion unless it's acutely worse.

BUN threshold is different in SI units

BUN > 19 mg/dL equals urea > 7 mmol/L. Make sure you're using the correct threshold for your laboratory's reporting units. For comprehensive renal assessment, use [Creatinine Clearance](/tools/creatinine-clearance) or [eGFR Calculator](/tools/egfr-calculator).

Re-assess if clinical status changes

CURB-65 is a snapshot. A patient with initial score of 1 who deteriorates over hours should be re-evaluated. Serial assessment is part of good clinical care.

Don't forget aspiration risk

Aspiration pneumonia and hospital-acquired pneumonia have different microbiology and may warrant admission regardless of CURB-65 score for appropriate antibiotic coverage.

Common Questions About Your Results

Evidence-Based Methodology

CURB-65 was derived and validated by Lim et al. in a 2003 study published in Thorax involving over 1,000 patients with community-acquired pneumonia. It is endorsed by the British Thoracic Society (BTS) guidelines for CAP management and is referenced in IDSA/ATS and European Respiratory Society guidelines as a validated severity assessment tool.

Clinical Content Trust

Last reviewed:: April 21, 2026
Guideline version:: General evidence framework v2026.04
Source set version:: Primary-source set v1

How to Interpret Your Result

Your CURB-65 score ranges from 0 to 5 and estimates 30-day mortality risk in community-acquired pneumonia. A score of 0 carries approximately 0.6% mortality risk, and a score of 1 carries approximately 2.7% — both considered low risk. A score of 2 corresponds to roughly 6.8–9.2% mortality (moderate risk). A score of 3 carries approximately 14.5% mortality, score 4 approximately 40%, and score 5 approximately 57% — all high risk.

The score directly informs disposition decisions. Patients with scores of 0–1 are generally safe for outpatient treatment with oral antibiotics. A score of 2 warrants consideration of short-stay hospitalization or closely supervised outpatient management. Scores of 3–5 require hospitalization, and scores of 4–5 should prompt consideration of intensive care unit admission.

When to Use This Tool

Use this calculator when assessing an adult patient with community-acquired pneumonia (CAP) to determine the appropriate level of care — outpatient treatment, hospital ward admission, or ICU admission. It is recommended by the British Thoracic Society (BTS) and is widely used in emergency departments and primary care settings.

It is particularly useful for supporting safe discharge decisions in patients who appear clinically well — a CURB-65 score of 0–1 provides objective evidence to support outpatient management, reducing unnecessary hospitalizations. It is also valuable for triaging patients during periods of high hospital census or during pneumonia outbreaks when bed availability is limited.

Limitations

CURB-65 does not account for important prognostic factors such as comorbidities (COPD, immunosuppression, heart failure), bilateral or multilobar infiltrates on imaging, pleural effusion, hypoxia (SpO2 or PaO2), lactate levels, or the specific causative pathogen. A young patient with severe hypoxia and bilateral infiltrates may score 0 on CURB-65 if they are not confused, have normal BUN, normal respiratory rate, and normal blood pressure.

The score was developed and validated for community-acquired pneumonia and should not be applied to hospital-acquired pneumonia, ventilator-associated pneumonia, or pneumonia in immunocompromised patients (e.g., HIV, transplant recipients, chemotherapy patients), where different severity assessment tools are needed. The Pneumonia Severity Index (PSI/PORT score) is a more comprehensive alternative that incorporates comorbidities and laboratory data, though it is more complex to calculate. Clinical judgment should always supplement the CURB-65 score, especially when the score seems discordant with the patient's overall clinical appearance.

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.

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April 21, 2026 · trust-baseline
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