CURB-65: how the pneumonia severity score is calculated
CURB-65 is a score for community-acquired pneumonia that gives 1 point each for five items: new Confusion, raised Urea (over 7 mmol/L), a Respiratory rate of 30 or more, low Blood pressure (systolic under 90 mm Hg or diastolic 60 or less), and age 65 or older. The total runs from 0 to 5.
Not a medical device. Not a diagnosis or dosing recommendation.
What is CURB-65?
CURB-65 comes from a 2003 paper by Lim, van der Eerden, Laing and colleagues in Thorax. The paper's title is about defining community-acquired pneumonia severity on presentation to hospital. The name spells out the five items.
This page explains the arithmetic. It doesn't turn a score into a decision about where someone is cared for, and it doesn't say what a score means for a particular person.
The CURB-65 formula
CURB-65 = confusion (1)
+ urea > 7 mmol/L (1)
+ respiratory rate ≥ 30 (1)
+ low blood pressure (1)
+ age ≥ 65 (1)
maximum = 5Exact expression the calculator uses:
CURB-65 = confusion + urea_high + respiratory_rate_ge_30 + low_blood_pressure + age_ge_65; max 5What each part means
| Letter | What earns a point | Points |
|---|---|---|
| C | New confusion | 1 |
| U | Urea over 7 mmol/L | 1 |
| R | Respiratory rate of 30 or more per minute | 1 |
| B | Systolic pressure under 90 mm Hg or diastolic pressure of 60 mm Hg or less | 1 |
| 65 | Age 65 or older | 1 |
How the score works
- Confusion. New confusion adds 1.
- Urea. Urea over 7 mmol/L adds 1.
- Respiratory rate. 30 or more breaths per minute adds 1.
- Blood pressure. Systolic under 90 or diastolic 60 or less adds 1. Either one is enough.
- Age. 65 or older adds 1.
- Add them up. The total is 0 to 5.
Inputs come from the user
The record says confusion, urea, respiratory rate and blood pressure are true/false answers from the person using the calculator. The urea answer is whether urea is over 7 mmol/L; Magent's calculator doesn't convert BUN in mg/dL. It takes age from 18 to 120 and returns the total, the maximum of 5, the age it used and a line for each item.
Worked example
This is the worked example in Magent's record for the calculator.
Example 1: age 70, confusion, urea high
- Confusion → 1. Urea over 7 mmol/L → 1.
- Respiratory rate and blood pressure items are false → 0.
- Age 70 is 65 or older → 1.
- Score = 3 out of 5.
Values at the boundaries
All are Magent's expected values for the calculator.
- Age 40 with every item false → 0.
- Age 65 with every item false → 1.
- Age 80 with every item true → 5.
History of CURB-65
The score comes from Lim WS, van der Eerden MM, Laing R and colleagues, Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study, Thorax, 2003 (volume 58, issue 5, pages 377–382).
When it's used
The paper's title places the score at presentation to hospital with community-acquired pneumonia.
Where it's used
The inputs are a mental-status finding, one blood test, two vital signs and age.
Who uses it
The person using the calculator assigns each finding. The calculator does the adding.
Limits of the calculation
- It adds up points. It isn't a decision about where someone is cared for.
- The urea item is a true/false answer. The calculator doesn't convert BUN in mg/dL to urea in mmol/L.
- This page doesn't say what to do with a score.
Clinical decisions belong to a qualified clinician who knows the patient.
How it differs from related calculators
- CRB-65 is the same score without the urea item, so its maximum is one point lower.
- Wells score for PE and Wells score for DVT are separate point scores for suspected blood clots.
Glossary
- Community-acquired pneumonia: a lung infection picked up outside a hospital.
- Urea: a waste product measured in the blood, reported in mmol/L.
- BUN: blood urea nitrogen, reported in mg/dL.
- Systolic / diastolic pressure: the higher and lower numbers in a blood pressure reading.
Common mistakes
- Answering the urea item from a BUN value without converting. The item asks whether urea is over 7 mmol/L.
- Needing both blood pressure readings to be low. Systolic under 90 or diastolic 60 or less is enough.
- Giving a point for age under 65. The age point starts at 65.
- Mixing up CURB-65 and CRB-65. CRB-65 leaves out urea.
Source
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
Frequently asked questions
How do you calculate CURB-65?
Give 1 point each for new confusion, urea over 7 mmol/L, respiratory rate of 30 or more, low blood pressure (systolic under 90 or diastolic 60 or less), and age 65 or older. Add them up for a total of 0 to 5.
What does a CURB-65 score of 2 mean?
This page doesn't give a cutoff or an outcome by score. It adds up the points; what a score means depends on the person and the clinical context.
What does CURB-65 stand for?
Confusion, Urea, Respiratory rate, Blood pressure, and age 65.
Can I use BUN instead of urea?
The calculator's urea item is a true/false answer to whether urea is over 7 mmol/L. It doesn't convert BUN.
Who developed CURB-65?
Lim and colleagues, in a 2003 paper in Thorax.