CRB-65: how the score is calculated without urea

CRB-65 is a community-acquired pneumonia score that gives 1 point each for four items: new Confusion, 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. It's CURB-65 without the urea blood test, so the total runs from 0 to 4.

Not a medical device. Not a diagnosis or dosing recommendation.

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Infection and VTE calculators
Lim WS et al. · 2003
The CRB-65 formula
Worked examples
Frequently asked questions

What is CRB-65?

Magent's record cites the 2003 paper by Lim, van der Eerden, Laing and colleagues in Thorax, the paper that derived CURB-65. CRB-65 uses the same letters with the U for urea left out.

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 CRB-65 formula

CRB-65 = confusion (1)
       + respiratory rate ≥ 30 (1)
       + low blood pressure (1)
       + age ≥ 65 (1)
maximum = 4

Exact expression the calculator uses:

CRB-65 = confusion + respiratory_rate_ge_30 + low_blood_pressure + age_ge_65; max 4

What each part means

Letter	What earns a point	Points
C	New confusion	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.
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; 64 adds nothing.
Add them up. The total is 0 to 4.

Inputs come from the user

The record says confusion, respiratory rate and blood pressure are true/false answers from the person using the calculator, assigned the same way as for CURB-65. Magent's calculator doesn't take blood pressure numbers. It takes age from 18 to 120 and returns the total, the maximum of 4, the age it used and a line for each item.

Worked examples

These are the worked examples in Magent's record for the calculator.

Example 1: age 40, every item false

Confusion, respiratory rate and blood pressure items are false → 0.
Age 40 isn't 65 or older → 0.
Score = 0 out of 4.

Example 2: age 70 with confusion

Confusion → 1.
Age 70 is 65 or older → 1.
Score = 2 out of 4.

Values at the boundaries

Each line changes Example 1. All are Magent's expected values for the calculator.

Confusion alone → 1. Respiratory rate item alone → 1. Low blood pressure alone → 1.
Age 64 → 0; age 65 → 1.
Age 80 with every item true → 4.

History of CRB-65

Magent's record cites 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 cited paper's title is about community-acquired pneumonia severity on presentation to hospital.

Where it's used

Every input is a bedside finding or the person's age. There's no blood test.

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.
It's CRB-65, with no urea item. It isn't CURB-65.
The blood pressure item is a true/false answer; the calculator doesn't take pressure readings.
This page doesn't say what to do with a score.

Clinical decisions belong to a qualified clinician who knows the patient.

CURB-65 adds a fifth item for raised urea, so its maximum is 5.

Glossary

Community-acquired pneumonia: a lung infection picked up outside a hospital.
Respiratory rate: breaths per minute.
Systolic / diastolic pressure: the higher and lower numbers in a blood pressure reading.

Common mistakes

Adding a urea point. CRB-65 has no urea item.
Needing both blood pressure readings to be low. Systolic under 90 or diastolic 60 or less is enough.
Giving age 64 a point. The age point starts at 65.

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 CRB-65?

Give 1 point each for new confusion, 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 4.

What does a CRB-65 score of 1 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 is the difference between CRB-65 and CURB-65?

CURB-65 includes raised urea as a fifth item. CRB-65 leaves it out, so it needs no blood test.