CURB-65 Pneumonia Severity Calculator

Understanding the CURB-65 score — concept and principle

CURB-65 is a five-point score that estimates the severity of community-acquired pneumonia in adults. Clinicians use it alongside their judgement to decide whether a patient can be treated at home, needs hospital admission or may need intensive care.

How it is calculated

One point for each of:

• C new confusion
• U urea above 7 mmol/L (blood urea nitrogen above 19 mg/dL)
• R respiratory rate 30 breaths/min or more
• B blood pressure: systolic below 90 mmHg or diastolic 60 mmHg or less
• 65 age 65 or over

The total ranges from 0 to 5. This calculator groups 0–1 as low severity, 2 as moderate and 3 or more as high. CRB-65 is the same score without urea, for use where blood tests are not available.

The principle

Each item reflects a way pneumonia threatens life. Confusion and low blood pressure suggest the infection is affecting the brain and circulation; a fast breathing rate signals respiratory strain; raised urea suggests dehydration or reduced kidney perfusion; older age lowers physiological reserve. Lim and colleagues (2003) derived and validated the score in hospital cohorts in the UK, New Zealand and the Netherlands, simplifying an earlier British Thoracic Society (BTS) rule into an easily remembered form. Thirty-day mortality rises steeply with each point.

Worked example

1. Defaults: no confusion, urea not raised, respiratory rate below 30, blood pressure not low, age under 65.
2. CURB-65 = 0 + 0 + 0 + 0 + 0 = 0.
3. 0 is 1 or less, so severity is low (30-day mortality ~1–3%).
4. For comparison, a 70-year-old with new confusion scores 2, which is moderate (~9%).

How to read the result

The BTS approach is broadly: 0–1, low severity, often suitable for home treatment; 2, moderate, consider a short hospital stay or hospital-supervised outpatient care; 3 or more, high severity, manage in hospital as severe pneumonia and assess for critical care, especially at 4–5. Low oxygen saturation, other illnesses or social circumstances can justify admission even at a low score.

Common mistakes

• Using the score for hospital-acquired pneumonia or in children; it was developed for adult community-acquired pneumonia.
• Mixing up urea and BUN units; 7 mmol/L urea corresponds to about 19 mg/dL BUN.
• Ignoring oxygen saturation, which is not part of the score.

Frequently asked questions

When should CRB-65 be used instead?

In primary care or the community, where a blood urea result is not immediately available.

Does a low score mean antibiotics are not needed?

No. CURB-65 grades severity, not whether an infection is bacterial; treatment is a separate decision.

How does it compare with the Pneumonia Severity Index?

The PSI uses about 20 variables and is better at identifying very low-risk patients, but CURB-65 is quicker to calculate.

Sources: Lim W. S. et al., Thorax, 2003 (derivation and validation of CURB-65) · British Thoracic Society, Guidelines for the management of community acquired pneumonia in adults