CURB-65 Score Calculator

CURB-65 Score Calculator for Pulmonology. In the original cohort, 30-day mortality rose steeply with score: 0.7% at 0, 3.2% at 1, 3% at 2, 17% at 3, 41.5% at 4, and 57% at 5. Scores 0 to 1 identify low-risk patients often suitable for outpatient treatment; a score of 2 suggests a short inpatient stay or closely supervised outpatient care; scores of 3 or higher flag severe pneumonia warranting admission with assessment for intensive care, especially at 4 to 5. The score's main value is safely identifying the low-risk group and escalating attention as the count climbs.

How this calculator works

CURB-65 is a five-item severity score for community-acquired pneumonia (CAP), awarding one point each for Confusion (new disorientation), Urea greater than 7 mmol/L (BUN greater than roughly 19 mg/dL), Respiratory rate 30/min or higher, low Blood pressure (systolic below 90 mmHg or diastolic 60 mmHg or lower), and age 65 or older, for a total of 0 to 5. It was derived by logistic regression against 30-day mortality; the simplified CRB-65 variant drops the urea term for settings without immediate bloodwork.

When to use this calculator

Use it at the point of initial hospital assessment in adults with radiographically confirmed CAP to triage site of care: outpatient management, short inpatient stay, or intensive care assessment. It is validated for prognosis in acute CAP and should not be used for hospital-acquired or ventilator-associated pneumonia, immunocompromised hosts, or as a standalone rule to send patients home. It does not replace clinical judgment about hypoxemia, decompensating comorbidity, or social factors that independently mandate admission.

Inputs used

  • Confusion
  • Urea/BUN
  • Respiratory rate
  • Blood pressure
  • Age

Clinical interpretation

In the original cohort, 30-day mortality rose steeply with score: 0.7% at 0, 3.2% at 1, 3% at 2, 17% at 3, 41.5% at 4, and 57% at 5. Scores 0 to 1 identify low-risk patients often suitable for outpatient treatment; a score of 2 suggests a short inpatient stay or closely supervised outpatient care; scores of 3 or higher flag severe pneumonia warranting admission with assessment for intensive care, especially at 4 to 5. The score's main value is safely identifying the low-risk group and escalating attention as the count climbs.

Worked example

A 72-year-old presents with CAP, BUN 24 mg/dL (urea about 8.6 mmol/L), respiratory rate 32/min, BP 128/78 mmHg, and no confusion. Points: age 65+ (1) + urea greater than 7 (1) + RR 30+ (1) = score 3. This places the patient in the high-risk band with roughly 17% 30-day mortality in the derivation cohort, supporting hospital admission with consideration of ICU-level assessment.

Limitations and safety notes

CURB-65 was derived for mortality prediction and can underestimate risk in younger patients with severe physiologic derangement but few points, and in hypoxemic patients since oxygenation is not scored. It performs less well at predicting ICU admission than tools built for that purpose, and can overweight age in elderly patients who are otherwise stable. It is not validated for aspiration pneumonia, immunosuppression (including neutropenia or HIV), or non-CAP respiratory infection, and comorbidity burden that drives admission is captured only indirectly.

Frequently asked questions

How does CURB-65 differ from the Pneumonia Severity Index (PSI/PORT)?

CURB-65 uses only five variables and is faster at the bedside, while PSI incorporates roughly 20 items including comorbidities and lab values and more finely identifies very low-risk patients. Both stratify 30-day mortality; PSI is more sensitive for the lowest-risk group, whereas CURB-65 is simpler. The 2019 ATS/IDSA guideline favors PSI over CURB-65 when choosing between them for the site-of-care decision.

What is the urea cutoff in conventional units?

The threshold is urea greater than 7 mmol/L, which corresponds to a blood urea nitrogen (BUN) above approximately 19 to 20 mg/dL. Labs reporting BUN in mg/dL should apply that value rather than the mmol/L number.

When should I use CRB-65 instead?

CRB-65 omits the urea term and is intended for community or primary-care settings where blood testing is not immediately available. It ranges 0 to 4 and still stratifies mortality, though it loses the discrimination the urea variable adds.

Does a low CURB-65 score alone justify outpatient treatment?

No. A score of 0 to 1 identifies a low-risk group, but hypoxemia, unstable comorbidities, inability to take oral therapy, or social barriers independently warrant admission regardless of the score. The score supports, but does not replace, the overall clinical assessment.

References

  • 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. PMID: 12728155.
  • Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med. 2019. PMID: 31573350.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: March 22, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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