About the CURB-65 Calculator
CURB-65 is a five-point severity score for adults with community-acquired pneumonia. One point each is given for Confusion, Urea over 7 mmol/L, Respiratory rate of 30 or more, low Blood pressure (systolic under 90 or diastolic 60 mmHg or less) and age 65 or older. It was derived and validated by Lim and colleagues in 2003 in 1,068 adults admitted with pneumonia in the UK, New Zealand and the Netherlands, and is used in the British Thoracic Society and NICE guidelines.
This calculator takes the raw observations — you enter the urea (or US blood urea nitrogen), respiratory rate, blood pressure and age, and it decides which criteria are met. It reports the score, the 30-day mortality seen at that score in the derivation cohort, and the low, intermediate or high risk group from NICE guideline NG250, with the place-of-care options NICE suggests considering.
If no blood test is available — for example in general practice — switch off the urea field to use CRB-65, the four-item version NICE recommends in primary care. Either score supports, but never replaces, clinical judgement: oxygen levels, comorbidities, pregnancy and social circumstances all matter.
With the default inputs, the score is 2. Change any value above to recalculate instantly.
How to use the curb-65 calculator
- 1Confirm the patient is an adult with clinically or radiologically diagnosed community-acquired pneumonia.
- 2Mark whether there is new confusion.
- 3Enter the urea (mmol/L) or BUN (mg/dL), or switch it off to use CRB-65.
- 4Enter respiratory rate, blood pressure and age.
- 5Read the score, risk group and mortality, and combine them with clinical judgement.
Formula and method
One point is scored for each feature present: new confusion (AMT ≤ 8 or new disorientation), urea above 7 mmol/L, respiratory rate of 30 breaths per minute or more, systolic pressure below 90 mmHg or diastolic 60 mmHg or less, and age 65 or older. A US blood urea nitrogen value is converted to urea by dividing by 2.8 (the mass of the two nitrogen atoms in one millimole of urea), so the urea criterion corresponds to a BUN above about 19.6 mg/dL.
In Lim et al.’s derivation cohort, 30-day mortality was 0.7%, 3.2%, 3%, 17%, 41.5% and 57% for scores 0 to 5. NICE NG250 groups CURB-65 as low (0–1, < 3%), intermediate (2, 3–15%) and high risk (3–5, > 15%), and CRB-65 as low (0, < 1%), intermediate (1–2, 1–10%) and high risk (3–4, > 10%).
- C
- New confusion
- U
- Urea > 7 mmol/L
- R
- Respiratory rate ≥ 30/min
- B
- Systolic BP < 90 or diastolic BP ≤ 60 mmHg
- 65
- Age ≥ 65 years
Worked examples
72-year-old with raised urea
Urea of 8.2 mmol/L (above 7) and age 72 score one point each; respiratory rate 24 and blood pressure 118/70 do not. A CURB-65 of 2 had 3% 30-day mortality in the derivation cohort and falls in the NICE intermediate-risk group.
US patient, BUN 32 mg/dL, hypotensive and confused
BUN 32 mg/dL ÷ 2.8 ≈ 11.4 mmol/L urea, above 7. With confusion, a respiratory rate of 32, systolic pressure 86 and age 81, all five criteria are met. A score of 5 carried 57% 30-day mortality in the derivation cohort.
Young adult in general practice (CRB-65)
Without a blood test, CRB-65 is used. A 38-year-old with normal respiratory rate and blood pressure and no confusion scores 0 — NICE low risk, with mortality under 1%.
Frequently asked questions
What does a CURB-65 score of 2 mean?+
A score of 2 is intermediate risk: 30-day mortality was about 3% in the derivation cohort and NICE puts this group at 3–15%. Hospital-based care or alternatives such as a virtual ward are usually considered.
What urea level counts for CURB-65?+
Urea above 7 mmol/L scores a point. In US units this is a blood urea nitrogen above roughly 19–20 mg/dL, since urea in mmol/L equals BUN in mg/dL divided by 2.8.
What is the difference between CURB-65 and CRB-65?+
CRB-65 drops the urea criterion so it can be used without a blood test, typically in general practice. NICE uses CRB-65 in the community and CURB-65 in hospital.
Is CURB-65 valid for hospital-acquired or aspiration pneumonia?+
No. It was derived in adults with community-acquired pneumonia and does not apply to hospital-acquired pneumonia, ventilator-associated pneumonia, children or severely immunocompromised patients.
How does CURB-65 compare with the Pneumonia Severity Index?+
The PSI uses 20 variables and is slightly better at identifying very low-risk patients, but CURB-65 is much quicker and is the score recommended by UK guidelines.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.