How the CURB-65 Pneumonia Severity Score Works
CURB-65 is a validated clinical prediction rule — developed by Lim and colleagues for the British Thoracic Society — that estimates 30-day mortality risk in adults with community-acquired pneumonia and helps guide the choice between outpatient treatment, hospital admission, and intensive care. One point is awarded for each of five criteria that is present, giving a total score from 0 to 5.
The five CURB-65 criteria
- C — Confusion: new disorientation to person, place, or time (or an abbreviated mental test score of 8 or less).
- U — Urea: blood urea nitrogen (BUN) above about 19 mg/dL, equivalent to a serum urea above 7 mmol/L.
- R — Respiratory rate: 30 breaths per minute or higher.
- B — Blood pressure: systolic blood pressure below 90 mmHg, or diastolic blood pressure of 60 mmHg or below.
- 65 — Age: 65 years or older.
How the score maps to a care setting
Add one point for each criterion present. A score of 0–1 corresponds to low severity, with an estimated 30-day mortality risk of roughly 1–3%; outpatient treatment may be appropriate for otherwise stable patients. A score of 2 corresponds to moderate severity (about 9% estimated mortality), and hospital-supervised care — either a short inpatient stay or closely monitored outpatient treatment — is generally recommended. A score of 3–5 corresponds to high severity, with mortality estimates rising from roughly 15% at a score of 3 to well over 25–40% at scores of 4–5; these patients should be treated as inpatients, with urgent assessment for ICU-level care at the higher scores.
Common mistakes and limitations
- Mixing urea units: BUN (mg/dL, common in the US) and urea (mmol/L, common elsewhere) differ by a factor of about 2.8 — select the correct unit before entering a value.
- Confusing the blood pressure rule: either a low systolic reading (below 90 mmHg) OR a low diastolic reading (60 mmHg or below) earns the blood pressure point — the two are not required together.
- Treating CURB-65 as the whole picture: the score does not include oxygen saturation, chest imaging, comorbidities, or social circumstances (such as the ability to take oral medication or return if symptoms worsen), all of which affect a real-world admission decision.
When to seek urgent care
CURB-65 is a screening and severity-estimation tool, not a diagnosis or a treatment order, and this calculator is for educational and reference purposes only. Anyone with suspected pneumonia and any CURB-65 risk factors — or with breathing difficulty, confusion, chest pain, or a rapid heart rate — should be evaluated by a clinician promptly; seek emergency care immediately for severe breathing difficulty, bluish lips or face, or collapse.