CURB-65 Score Calculator
Enter confusion status, blood urea, respiratory rate, blood pressure and age to get the CURB-65 score, severity category and suggested care setting for community-acquired pneumonia.
Assess Community-Acquired Pneumonia Severity
CURB-65 Score Formula
Where:
- \(C\) — confusion of new onset (1 point if present)
- \(U\) — blood urea above 7 mmol/L, equivalent to 19.6 mg/dL of urea (1 point)
- \(R\) — respiratory rate of 30 breaths/min or more (1 point)
- \(B\) — low blood pressure: systolic below 90 mmHg or diastolic 60 mmHg or below (1 point)
- \(A_{65}\) — age of 65 years or older (1 point)
The score is the simple sum of the five criteria, so it ranges from 0 to 5, with higher values indicating more severe pneumonia and a higher risk of death.
CURB-65 Score – Calculation Example
Example: a 70-year-old patient with pneumonia has no new confusion, a blood urea of 8 mmol/L, a respiratory rate of 24 breaths/min, a blood pressure of 110/65 mmHg.
\[
C = 0, \; U = 1 \; (8 > 7), \; R = 0 \; (24 60), \; A_{65} = 1 \; (70 \geq 65)
\]
\[
\text{CURB-65} = 0 + 1 + 0 + 0 + 1 = 2
\]
Result: a CURB-65 score of 2 — moderate severity, estimated 30-day mortality about 6.8%; a short hospital admission or supervised outpatient care should be considered.
How to use the calculator
- Tick the Confusion (new disorientation) checkbox only if mental confusion has been newly noted by family or caregivers — long-standing confusion does not count.
- Enter the Blood urea value and select the matching unit, mmol/L or mg/dL; the threshold of 7 mmol/L corresponds to 19.6 mg/dL.
- Enter the Respiratory rate in breaths per minute, measured while the patient is at rest.
- Enter the Systolic blood pressure and Diastolic blood pressure in mmHg.
- Enter the patient's Age in years.
- Read the CURB-65 score, the severity category with the recommended care setting, and the interpretation of which criteria were met.
What the CURB-65 score is
CURB-65 is a clinical prediction rule used to assess the severity of community-acquired pneumonia (CAP) — pneumonia caught outside a hospital setting. It was derived by Lim and colleagues and published in Thorax in 2003 as a simplification of the earlier BTS rule. The name is an acronym of the five criteria: Confusion, Urea, Respiratory rate, Blood pressure, and age 65 or older.
The score's main purpose is to guide the decision of where to treat the patient. Each point roughly corresponds to an increase in the risk of dying within 30 days. In the original cohort, mortality was about 0.6% at score 0, 3% at score 1, 6.8% at score 2, and 14–28% at scores 3–5. In practice, scores of 0–1 usually support treatment at home with oral antibiotics, a score of 2 warrants considering admission or closely supervised outpatient care, and scores of 3–5 indicate hospital admission, with intensive care assessment often appropriate at 4–5.
Because it needs only a brief mental-status check, one blood test and three bedside measurements, CURB-65 can be applied quickly in emergency departments, primary care and telemedicine triage. It is one of the most widely used severity tools for CAP alongside the PSI/PORT score, which is more detailed but slower to compute. If confusion is present, formal scoring with the Glasgow Coma Scale can help document the level of consciousness.
Reference table
| Score | Severity | Typical 30-day mortality | Suggested care setting |
|---|---|---|---|
| 0–1 | Low | 0.6–3% | Outpatient treatment with oral antibiotics |
| 2 | Moderate | about 6.8% | Short hospital admission or supervised outpatient care |
| 3 | High | about 14% | Hospital admission |
| 4–5 | High | up to about 28% | Hospital admission, often with ICU assessment |
Assumptions, limitations and practical tips
- It is a decision aid, not a diagnosis. CURB-65 estimates mortality risk but does not replace clinical judgment. Hypoxemia (low oxygen saturation), serious comorbidities, immunosuppression, pregnancy, vomiting or inability to take oral antibiotics, and poor social support can all justify admission even at a low score.
- Only new confusion counts. Chronic confusion from dementia or other causes should not be scored; ask caregivers whether the mental state has changed with the current illness.
- Watch the urea units. The threshold is urea above 7 mmol/L, which is 19.6 mg/dL of urea. Note that some laboratories report blood urea nitrogen (BUN) instead — the BUN threshold is about 20 mg/dL, which coincidentally is numerically close but conceptually different; be sure of what your lab measures.
- One blood-pressure reading is enough for the rule, but a single abnormal reading can be misleading. If in doubt, repeat the measurement. For a fuller picture of circulatory status you can also compute the mean arterial pressure.
- Elevated urea may reflect kidney disease or dehydration rather than severe infection alone; a persistently raised value is worth evaluating separately, for example with the eGFR (CKD-EPI 2021) calculator.
- The mortality figures are approximations from the original UK derivation cohort (Lim et al., Thorax 2003) and may differ in other populations, age groups and healthcare systems.
- The rule was designed for community-acquired pneumonia in adults. It does not apply to hospital-acquired pneumonia, immunocompromised patients or children.
Frequently Asked Questions
How do I calculate the CURB-65 score by hand?
Give one point for each of five findings and add them up: new-onset confusion, urea above 7 mmol/L, respiratory rate of 30 breaths/min or more, systolic pressure below 90 mmHg or diastolic pressure of 60 mmHg or below, and age 65 or older. The total ranges from 0 to 5. No laboratory result beyond urea is needed, so the rule can be scored at the bedside in about a minute.
Is blood urea the same as BUN, and how do I convert the units?
No — they are different measurements of the same substance. BUN reports only the nitrogen content of urea. To convert: urea in mmol/L × 2.8 = urea in mg/dL, and urea in mg/dL × 0.467 = BUN in mg/dL. The CURB-65 threshold of urea > 7 mmol/L equals 19.6 mg/dL of urea or roughly 20 mg/dL of BUN. Always check which quantity your lab reports before entering a value.
What is a good or dangerous CURB-65 score?
A score of 0 or 1 is considered low risk — roughly 0.6–3% 30-day mortality — and usually supports home treatment. A score of 2 is moderate risk (about 6.8%) and typically prompts consideration of hospital admission. Scores of 3–5 are high risk (roughly 14–28%) and warrant inpatient care, with ICU evaluation often advised at 4–5. These are population averages, not predictions for an individual patient.
What are the most common mistakes when using CURB-65?
Frequent errors include: scoring long-standing dementia as "confusion" (only new mental changes count); using the wrong urea unit or confusing BUN with urea; forgetting that a diastolic pressure of exactly 60 mmHg scores a point; missing that a respiratory rate of exactly 30 also scores; and relying on a single abnormal blood-pressure reading. Also remember the rule applies only to community-acquired pneumonia in adults, not to children or hospital-acquired infections.
How does CURB-65 compare with the PSI/PORT score and qSOFA?
The PSI/PORT score is more accurate for predicting mortality but requires around 20 variables, including imaging and additional labs, so it is slower. CURB-65 trades some precision for speed and simplicity. qSOFA (respiratory rate ≥ 22, altered mentation, systolic pressure ≤ 100) is a general screening tool for sepsis risk, not pneumonia-specific. In practice CURB-65 is the quickest tool focused specifically on pneumonia severity and the admission decision.
Does a low CURB-65 score guarantee that home treatment is safe?
No. CURB-65 measures mortality risk, not the full clinical picture. Factors the score ignores include low oxygen saturation, serious comorbidities such as heart failure or COPD, immunosuppression, pregnancy, inability to swallow oral antibiotics or keep them down, and lack of support at home. Any of these can justify admission despite a score of 0 or 1. The score is a triage aid — the final decision always rests with the treating clinician.
Why does confusion count only if it is new?
Because the criterion signals an acute change in brain function caused by the infection, which marks severe illness. Chronic confusion from dementia or other long-standing causes is unrelated to the current pneumonia and would overstate severity if scored. Ask relatives or caregivers whether the patient's mental state has clearly changed with this illness — disorientation to person, place or time that appeared recently. If present, documenting it with the Glasgow Coma Scale can add useful detail.