CURB-65 and CRB-65 Pneumonia Severity

Admit or treat at home, and CRB-65 when there is no urea to hand · v1.0

  • Answer each of the five criteria. Every threshold is written into the question, worded as the derivation paper words it, so nothing has to be remembered.
  • Urea is the one that takes a value, because the criterion is 42 mg/dL of blood urea and a report quoting BUN needs multiplying by 2.14 first. The unit toggle takes mmol/L as well.
  • Without a urea, tick "urea not available" and the tool falls back to CRB-65, which was built for exactly that situation.
  • You get the score, the 30-day mortality band it carries, and where this patient should be treated.
  • Read the score as a floor, not a ceiling. A young patient with a low score who cannot take tablets reliably, or who has nobody at home to watch for deterioration, may still need admission.

  • Anybody below 18 years, since neither score is validated in children. The tool takes the criteria as answered and does not ask the age, so nothing here will stop a child being scored. Assess a child on paediatric criteria instead: work of breathing, oxygen saturation, feeding and hydration, and the age-specific respiratory rate.
  • Pneumonia that is not community-acquired. Both scores were derived in community-acquired disease, so hospital-acquired, ventilator-associated and aspiration pneumonia sit outside them.
  • The choice of antibiotic, which the Empirical Antimicrobial Pathway makes from the severity and setting decided here.
  • Hypoxaemia, decompensated comorbidity and social circumstances. Neither score takes an oxygen saturation or any of the rest as an input, and any of them can justify admission over a score that reads low.
  • The criteria for intensive care. A high score prompts assessment for HDU or ICU care and stops there.

The Five Criteria

Confusion new disorientation in person, place or time

Respiratory rate 30 per minute or above

Blood pressure systolic below 90 mmHg, or diastolic 60 mmHg or below

Age 65 years or above

Blood urea the criterion is above 42 mg/dL, or above 7 mmol/L

Blood urea, not BUN. A report quoting BUN needs multiplying by 2.14 first. Evidence & Pearls sets out why.

Clinical Disclaimer: CURB-65 and CRB-65 estimate 30-day mortality from community-acquired pneumonia. They do not account for hypoxaemia, decompensated comorbidity, social circumstances, or the patient's ability to take oral antibiotics reliably at home. Use the score to support a decision, not to make it.

Clinical Application

1. CRB-65 Exists Because Urea Is Not Always Available

CURB-65 needs a same-day urea, which a primary health centre without a laboratory cannot always provide. CRB-65 drops urea and keeps the other four criteria, and was validated for exactly that setting: a clinician with a blood pressure cuff, a watch, and a bedside assessment of confusion. It is the tool for a district or rural practice where the choice is CRB-65 today or no score at all.

2. Blood Urea, Not BUN

The original criterion is urea above 7 mmol/L, which is 42 mg/dL of blood urea, not BUN. Indian laboratory reports overwhelmingly quote blood urea directly. A report quoting BUN needs multiplying by roughly 2.14 to become blood urea in mg/dL before it is compared with this threshold; using a BUN value directly against the 42 mg/dL line under-calls the score.

3. The Score Is a Floor, Not a Ceiling

A low score describes low mortality risk from the pneumonia itself. It says nothing about a patient who cannot swallow tablets reliably, lives alone with nobody to observe deterioration, or has an unstable comorbidity such as poorly controlled diabetes or ischaemic heart disease. Any of these can justify admission over a score that reads low.

4. What Indian Validation Has Found

A study from an Indian tertiary centre compared CURB-65 against the Pneumonia Severity Index. CURB-65 was simpler to apply at the bedside and broadly concordant with outcomes. It carried the same caution most validation cohorts carry: neither score alone should override what the clinician makes of the patient in front of them.

5. This Tool Does Not Choose the Antibiotic

CURB-65 and CRB-65 answer "how sick is this pneumonia, and where should it be managed", not "which antibiotic". The Empirical Antimicrobial Pathway takes the severity and setting from here and works out the regimen.

Abbreviations BP (Blood Pressure) · BTS (British Thoracic Society) · BUN (Blood Urea Nitrogen) · CAP (Community-Acquired Pneumonia) · ICU (Intensive Care Unit) · NICE (National Institute for Health and Care Excellence) · PHC (Primary Health Centre) · PSI (Pneumonia Severity Index)
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.
  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.
  3. National Institute for Health and Care Excellence. Pneumonia: diagnosis and management. NICE guideline NG250. Published 2 September 2025.
  4. Ewig S, Schäfer H, Torres A. Severity assessment in community-acquired pneumonia. Eur Respir J. 2000;16(6):1193-1201.
  5. Chalmers JD, Singanayagam A, Akram AR, et al. Severity assessment tools for predicting mortality in hospitalised patients with community-acquired pneumonia: systematic review and meta-analysis. Thorax. 2010;65(10):878-883.
  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.
  7. Shah BA, Ahmed W, Dhobi GN, Shah NN, Khursheed SQ, Haq I. Validity of pneumonia severity index and CURB-65 severity scoring systems in community acquired pneumonia in an Indian setting. Indian J Chest Dis Allied Sci. 2010;52(1):9-17.
  8. Gupta D, Agarwal R, Aggarwal AN, et al. Guidelines for diagnosis and management of community- and hospital-acquired pneumonia in adults: joint ICS/NCCP(I) recommendations. Lung India. 2012;29(Suppl 2):S27-S62.
How to Cite This Tool

DOIhttps://doi.org/10.5281/zenodo.22401566

AMA Style:Umakanth S. CURB-65 and CRB-65 Pneumonia Severity. Version 1.0. MEDiscuss Clinical Decision Support System. Published 2026. Accessed . https://mediscuss.org/cdss/curb65-pneumonia-severity. doi:10.5281/zenodo.22401566

Vancouver Style:Umakanth S. CURB-65 and CRB-65 Pneumonia Severity [Internet]. Version 1.0. MEDiscuss.org; 2026 [cited ]. Available from: https://mediscuss.org/cdss/curb65-pneumonia-severity. doi:10.5281/zenodo.22401566

Disclaimer and scope
Disclaimer: This decision-support system is written for healthcare professionals. It does not substitute clinical judgment, and the treating physician retains absolute responsibility for every diagnostic, dosing and therapeutic decision. The algorithms are built on the evidence as it stands, and the evidence moves. Verify the output against your current institutional protocol, and against the patient in front of you.
© 2026 MEDiscuss.org. All rights reserved. Provided free of charge for clinical use. Unauthorised reproduction or redistribution is strictly prohibited.
Category Therapeutic & Management PathwaysPathway
Specialties Internal Medicine, Pulmonology, Infectious Diseases

Written and maintained by

Dr Shashikiran Umakanth

Last revised 24 August 2026

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