Health & Medicine · Clinical Scores · Infectious Disease
CURB-65 Score Calculator
Calculates the CURB-65 severity score for community-acquired pneumonia to guide inpatient versus outpatient management decisions.
Calculator
Formula
Each criterion contributes 1 point: C = Confusion (new disorientation to person, place, or time); U = Urea > 7 mmol/L (BUN > 19 mg/dL); R = Respiratory rate \geq 30 breaths/min; B = Blood pressure (systolic < 90 mmHg or diastolic \leq 60 mmHg); A_{65} = Age \geq 65 years. Scores range from 0–5. Score 0–1: low severity (outpatient); Score 2: moderate severity (consider short-stay or supervised outpatient); Score 3–5: high severity (hospitalize, consider ICU if score 4–5).
Source: Lim WS, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377–382. British Thoracic Society (BTS) Guidelines.
How it works
Community-acquired pneumonia is one of the most common infectious causes of hospitalization and death globally. Early risk stratification is essential because over-hospitalization wastes resources and exposes low-risk patients to hospital-acquired complications, while under-triage of high-risk patients leads to preventable mortality. The CURB-65 score was derived from a large international dataset and validated across multiple clinical settings to provide a simple, rapid, five-variable scoring system that any clinician can apply at the bedside without advanced imaging or laboratory panels.
The score assigns one point for each of five criteria: new-onset Confusion (assessed by abbreviated mental test or clinical judgment), elevated blood Urea nitrogen (BUN > 19 mg/dL or urea > 7 mmol/L reflecting renal impairment from systemic illness), elevated Respiratory rate (≥30 breaths/min indicating respiratory compromise), low Blood pressure (systolic < 90 mmHg or diastolic ≤60 mmHg indicating circulatory compromise), and Age ≥65 years as an independent risk modifier. The total score ranges from 0 to 5, with higher scores correlating directly with 30-day all-cause mortality.
Score interpretation follows three tiers: a score of 0–1 indicates low severity with an estimated 30-day mortality below 3%, supporting outpatient treatment with oral antibiotics. A score of 2 indicates moderate severity (estimated mortality ~6.8%), where short-stay hospitalization or closely supervised outpatient therapy is recommended. Scores of 3 or higher indicate high severity requiring hospital admission, and scores of 4–5 warrant consideration of ICU or high-dependency unit care given mortality risks exceeding 14–27%.
Worked example
Consider a 72-year-old male presenting to the emergency department with cough, fever, and altered mentation. On examination: he is confused and disoriented to time and place (C = 1), his BUN is 24 mg/dL (U = 1), his respiratory rate is 32 breaths/min (R = 1), his blood pressure is 118/72 mmHg — systolic above 90 and diastolic above 60 (B = 0), and his age is 72 years (A = 1).
CURB-65 = 1 + 1 + 1 + 0 + 1 = 4 points. This places the patient in the high-severity category with an estimated 30-day mortality of approximately 27.8%. The recommended management is hospital admission with strong consideration of ICU or high-dependency unit care, aggressive fluid resuscitation, IV antibiotics covering typical and atypical pathogens, and close monitoring of respiratory and hemodynamic parameters.
In contrast, a 45-year-old otherwise healthy woman with CAP, no confusion, BUN of 12 mg/dL, respiratory rate of 20 breaths/min, BP 125/80 mmHg scores 0 points. Her estimated 30-day mortality is only 0.6%, supporting safe outpatient treatment with oral amoxicillin or a macrolide.
Limitations & notes
The CURB-65 score, while widely validated, has several important limitations clinicians must recognize. It does not account for comorbidities such as chronic obstructive pulmonary disease, immunosuppression, liver cirrhosis, heart failure, or diabetes, all of which significantly worsen pneumonia prognosis and may necessitate hospitalization even at low CURB-65 scores. The score also does not incorporate oxygenation parameters — a patient with oxygen saturation of 88% on room air may score 0 but clearly requires close monitoring or admission. Furthermore, CURB-65 was developed and validated primarily in Western emergency department populations, and its performance may vary in different healthcare settings or patient demographics. Clinicians should always integrate CURB-65 with clinical judgment, patient preferences, social circumstances (e.g., ability to take oral medications and follow up reliably), and local antibiotic resistance patterns. The score is a decision-support tool, not a replacement for comprehensive clinical assessment. In resource-limited settings, the simpler CRB-65 score (which excludes the BUN criterion) may be preferable when laboratory results are not immediately available.
Frequently asked questions
What is a CURB-65 score of 2 recommend for management?
A CURB-65 score of 2 indicates moderate severity community-acquired pneumonia with an estimated 30-day mortality of approximately 6.8%. The British Thoracic Society recommends considering short-stay inpatient admission or closely supervised outpatient management with early follow-up. Clinical judgment regarding comorbidities and social support should also inform the decision.
How does CURB-65 differ from the Pneumonia Severity Index (PSI)?
CURB-65 uses five simple binary criteria and is rapid to calculate at the bedside, making it practical in busy emergency settings. The Pneumonia Severity Index (PSI/PORT score) uses 20 variables including demographics, comorbidities, and laboratory results, providing more granular risk stratification but requiring significantly more data. CURB-65 tends to be better at identifying high-risk patients, while PSI is better at identifying low-risk patients suitable for outpatient care.
Can CURB-65 be used for hospital-acquired pneumonia?
No. CURB-65 was derived and validated specifically for community-acquired pneumonia (CAP) presenting to hospital. Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) have different causative organisms, resistance profiles, and risk factors. Separate clinical assessment frameworks and local antibiograms guide management of HAP and VAP.
What does the 65 in CURB-65 stand for?
The '65' refers to the age criterion of 65 years or older. Age ≥65 is an independent predictor of increased 30-day mortality from community-acquired pneumonia and contributes one point to the total CURB-65 score. The CURB acronym itself stands for Confusion, Urea, Respiratory rate, and Blood pressure — the other four clinical variables.
What is CRB-65 and when should it be used instead of CURB-65?
CRB-65 is a simplified version of CURB-65 that omits the blood urea nitrogen (BUN) criterion, making it suitable for use in primary care or resource-limited settings where laboratory testing is not immediately available. It uses only Confusion, Respiratory rate, Blood pressure, and Age ≥65. While slightly less precise, CRB-65 has been validated as a reliable bedside tool for initial pneumonia risk stratification when BUN results cannot be rapidly obtained.
Last updated: 2025-01-15 · Formula verified against primary sources.