CURB-65 Score: Pneumonia Severity Explained

Community-acquired pneumonia can look almost identical from one patient to the next at first glance — cough, fever, an infiltrate on the chest X-ray — yet outcomes range from a straightforward week of oral antibiotics at home to a multi-week ICU admission. CURB-65 is the tool most emergency physicians, hospitalists, and primary care clinicians reach for to tell those two pictures apart at the bedside, in under a minute, using nothing more than a set of vital signs, a single blood test, and the patient’s age.

What CURB-65 actually measures

CURB-65 is an acronym for its five criteria, each worth one point if present: new-onset Confusion; blood Urea above 7 mmol/L, roughly equivalent to a BUN above 19 mg/dL; a Respiratory rate of 30 breaths per minute or higher; low Blood pressure, meaning a systolic under 90 mmHg or a diastolic at or below 60 mmHg; and age 65 or older. There’s no weighting or math beyond simple addition — a patient either meets a criterion or doesn’t, and the five add up to a score between 0 and 5. That simplicity is the point: it was designed to be calculated from information already sitting in front of a clinician at triage, without waiting on additional labs or imaging.

Why the mortality bands matter

What makes CURB-65 clinically useful isn’t the raw number so much as what it predicts. In the original derivation and validation cohort, a score of 0 or 1 tracked with roughly 1.5% 30-day mortality, a score of 2 tracked with roughly 9.2%, and a score of 3 or higher tracked with roughly 22%. Those bands map loosely onto a site-of-care decision: low scores are often appropriate for outpatient treatment, a middle score often prompts a short inpatient stay or closely supervised outpatient care, and a high score usually points toward admission, with scores of 4 or 5 prompting a conversation about whether ICU-level care is needed. A 72-year-old who is newly confused with a respiratory rate of 32, for instance, already has three points — confusion, respiratory rate, and age — and lands in that high-risk band before a single lab result is back.

What CURB-65 can’t tell you

CURB-65 was derived and validated specifically for community-acquired pneumonia, and it estimates mortality risk to help triage site-of-care — it isn’t a diagnostic test for pneumonia itself, and a low score doesn’t automatically make outpatient treatment the right call. The score says nothing directly about oxygen requirement or hypoxemia, nothing about a decompensated comorbidity like unstable heart failure, and nothing about whether a patient can realistically take oral antibiotics, get to a pharmacy, or attend follow-up. A clinician who overrides a low CURB-65 because the patient looks unwell, is hypoxic, or has nowhere safe to recover is using the score exactly as intended: as one input into judgment, not a replacement for it.

Editverse built a free, interactive CURB-65 calculator that walks through all five criteria, shows the approximate mortality band, and includes a fully worked example — useful for a quick bedside check or for teaching the score to a trainee. It cites its source directly: Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377–382.