CURB-65 Pneumonia Severity Score Calculator

CURB-65 is the severity score endorsed by the British Thoracic Society and NICE for adults with community-acquired pneumonia (CAP). It was derived and validated by Lim and colleagues in 2003 across cohorts in the UK, the Netherlands and New Zealand. It is a simple additive score — each of five findings present at first assessment adds one point, so the total runs from 0 to 5. There is no arithmetic beyond adding up the points.

The name is a mnemonic for the five criteria:

• C — Confusion (new-onset; AMTS ≤ 8) → 1
• U — Urea > 7 mmol/L (BUN > ~19 mg/dL) → 1
• R — Respiratory rate ≥ 30 breaths/min → 1
• B — Blood pressure: systolic < 90 mmHg or diastolic ≤ 60 mmHg → 1
• 65 — Age ≥ 65 years → 1

The total is score = C + U + R + B + 65. The urea criterion uses the canonical mmol/L cut-off; if your lab reports blood urea nitrogen in mg/dL, the tool converts with urea(mmol/L) = BUN(mg/dL) ÷ 2.8 before comparing to 7. The blood-pressure criterion is satisfied if either limb qualifies — systolic below 90 or diastolic at or below 60.

Each total maps to a published 30-day mortality from the Lim 2003 (Thorax international derivation/validation cohort): 0.6% at a score of 0, rising to about 27.8% at 4–5. Those figures are transcribed verbatim from the paper, not modelled. The care-setting bands follow BTS 2009 / NICE NG138 & CG191: 0–1 is low risk (usually suitable for home treatment), 2 is intermediate (consider a short inpatient stay or supervised outpatient care), and 3–5 is high risk (manage in hospital as severe pneumonia, and for 4–5 assess for intensive or high-dependency care).

Where blood tests are not available — primary care, an ambulance, a rural clinic — the tool also reports CRB-65, which drops the urea point for a 0–4 score. It is graded 0 (very low), 1–2 (intermediate) and 3–4 (high). Comparing the two shows how much the urea result changes the recommended setting.

• Lim WS, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax 2003;58:377–382 (original CURB-65 derivation & 30-day mortality)
• NICE NG138 — Pneumonia (community-acquired): antimicrobial prescribing (endorses CURB-65 / CRB-65 for care-setting stratification)
• British Thoracic Society — Guidelines for the management of community-acquired pneumonia in adults (care-setting recommendations by score band)

The criteria, 30-day mortality figures and care-setting bands on this page were last cross-checked against these sources on 2026-07-12. This tool is for education and reference only; it aids, but does not replace, assessment by a qualified clinician, and it is not intended for paediatric or immunocompromised-specific decisions.