CURB-65 Pneumonia Severity Score

Methodology

CURB-65 (Lim 2003; BTS 2009)

1 point each: Confusion, Urea > 7 mmol/L, RR ≥ 30, BP (SBP < 90 or DBP ≤ 60), age ≥ 65

Validated in hospital cohorts in the UK, New Zealand and the Netherlands.

Who it is for

Adults with community-acquired pneumonia.

Version

1.0.1

How this calculator works

Where the formula comes from

• CURB-65 was derived by Lim and colleagues (2003) from three prospective studies of community-acquired pneumonia in the UK, New Zealand and the Netherlands, using 80% of 1,068 patients for derivation and 20% for validation, with 30-day mortality as the outcome.^[1]
• The study reported 30-day mortality rising with the score: 0.7% at 0, 3.2% at 1, 3% at 2, 17% at 3, 41.5% at 4 and 57% at 5.^[1]

The inputs

• One point each for new confusion, urea over 7 mmol/L, respiratory rate 30/min or more, systolic blood pressure under 90 mmHg or diastolic 60 mmHg or less, and age 65 or over (score 0–5).^[1]
• Confusion is defined as new disorientation in person, place or time, or an abbreviated mental test score of 8 or less.^[2]

Versions and alternatives

• CRB-65 leaves out urea so it can be used without a blood test, for example in general practice.^[2][3]
• The Pneumonia Severity Index (1997) is an alternative severity and mortality-prediction rule for community-acquired pneumonia that combines demographic, comorbidity, examination and laboratory findings.^[4]

Where accuracy falls (published evidence)

• In a 2010 emergency-department study, CURB-65 discriminated less well in patients aged 85 or over (AUC 0.60) than in adults under 65 (0.80).^[5]

What guidelines say

• The BTS 2009 guideline recommends CURB-65 for severity assessment in hospital, alongside clinical judgement.^[2]
• The 2019 ATS/IDSA guideline recommends clinical judgement supplemented by a validated rule, preferably the Pneumonia Severity Index over CURB-65, to decide on outpatient or inpatient treatment.^[6]

Sources

1. 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. doi:10.1136/thorax.58.5.377
2. Lim WS, Baudouin SV, George RC, et al. BTS guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax. 2009;64(Suppl 3):iii1–iii55. doi:10.1136/thx.2009.121434
3. McNally M, Curtain J, O'Brien KK, Dimitrov BD, Fahey T. Validity of British Thoracic Society guidance (the CRB-65 rule) for predicting the severity of pneumonia in general practice: systematic review and meta-analysis. Br J Gen Pract. 2010;60(579):e423–e433. PMID 20883616
4. Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243–250. doi:10.1056/NEJM199701233360402
5. Chen JH, Chang SS, Liu JJ, et al. Comparison of clinical characteristics and performance of pneumonia severity score and CURB-65 among younger adults, elderly and very old subjects. Thorax. 2010;65(11):971–977. PMID 20965934
6. 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;200(7):e45–e67. doi:10.1164/rccm.201908-1581ST

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on 2026-10-11

Worked example: how to calculate CURB-65

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

• Supports, but does not replace, clinical judgement about admission.

References

1. 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. doi:10.1136/thorax.58.5.377
2. Lim WS, Baudouin SV, George RC, et al. BTS guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax. 2009;64(Suppl 3):iii1–iii55. doi:10.1136/thx.2009.121434