CURB-65 Score Calculator for Pneumonia Severity

About

The CURB-65 score was developed by Lim et al. as part of the British Thoracic Society (BTS) collaborative study, published in Thorax in 2003. It was designed as a simplified and validated severity assessment tool for community-acquired pneumonia (CAP) that could be readily calculated at the bedside. The score is derived from the earlier CURB score and incorporates five binary variables, each contributing 1 point: new-onset confusion (C), blood urea nitrogen greater than 19 mg/dL or urea greater than 7 mmol/L (U), respiratory rate of 30 breaths per minute or greater (R), systolic blood pressure below 90 mmHg or diastolic blood pressure 60 mmHg or less (B), and age 65 years or older (65). The total score ranges from 0 to 5, and the score correlates with 30-day mortality in a stepwise fashion. The validation cohort included over 80,000 patients across multiple countries. The CURB-65 score is recommended by the British Thoracic Society and the National Institute for Health and Care Excellence (NICE) for severity assessment in CAP. A related score called CRB-65 excludes the urea measurement and is appropriate for primary care settings where laboratory testing is unavailable. CURB-65 is one of the most widely used pneumonia severity scores globally due to its simplicity and robust validation.

Formula

CURB-65 = Confusion (1) + BUN > 19 (1) + RR ≥ 30 (1) + SBP < 90 or DBP ≤ 60 (1) + Age ≥ 65 (1)

The CURB-65 score is calculated by summing 1 point for each of five binary clinical variables present at the time of initial assessment. The "C" criterion (confusion) is defined as new-onset disorientation to person, place, or time, or a Mental Test Score of 8 or less — this reflects acute brain dysfunction due to infection, hypoxia, or metabolic derangement. The "U" criterion (urea) is met when blood urea nitrogen exceeds 19 mg/dL (equivalent to serum urea > 7 mmol/L or approximately 40 mg/dL of urea); azotemia in pneumonia reflects dehydration, renal hypoperfusion, or underlying chronic kidney disease. The "R" criterion (respiratory rate) is met when the respiratory rate is 30 breaths per minute or greater; tachypnea is a sensitive marker of respiratory distress and impending respiratory failure. The "B" criterion (blood pressure) is met when systolic blood pressure is below 90 mmHg or diastolic blood pressure is 60 mmHg or less; hypotension in pneumonia indicates possible sepsis with vasodilation or hypovolemia. The "65" criterion (age) is met when the patient is 65 years or older; age is an independent risk factor for mortality in pneumonia due to immunosenescence and reduced physiologic reserve. The total score ranges from 0 to 5. The 30-day mortality rate shows a clear stepwise increase: 0.6-2.7% for score 0-1, 6.8% for score 2, 14-17.5% for score 3, and 27.8% for scores 4-5. The score is used to guide site-of-care decisions: scores of 0-1 are suitable for outpatient management, score 2 may require short-stay hospital observation, and scores of 3-5 generally require inpatient admission with consideration for ICU for scores 4-5.

Score Interpretation

The CURB-65 score is formally recommended by the British Thoracic Society (BTS) guidelines for the management of community-acquired pneumonia in adults (updated 2009) and by the National Institute for Health and Care Excellence (NICE) guideline NG195 (2019) for assessing pneumonia severity and guiding antibiotic prescribing. The score serves as the primary severity assessment tool in the UK National Health Service and is widely used internationally. In clinical practice, CURB-65 helps clinicians make evidence-based decisions about: (1) site of care — whether to manage as an outpatient, short-stay observation, or inpatient; (2) antibiotic choice — oral vs. intravenous therapy; and (3) level of monitoring. A score of 0-1 identifies low-risk patients who can be safely treated at home with oral antibiotics, potentially reducing unnecessary hospital admissions. A score of 2 identifies patients who may benefit from a short period of hospital observation. Scores of 3-5 identify high-risk patients requiring inpatient care, with scores of 4-5 warranting ICU assessment. The BTS guidelines also recommend the CRB-65 version (which omits the urea measurement) for use in primary care settings. Despite its widespread use, CURB-65 is less sensitive than the PSI/PORT score for identifying low-risk patients who can be safely treated as outpatients. Additionally, CURB-65 may underestimate severity in younger patients (who do not score for age) and does not account for important comorbidities, hypoxia, or social factors that may influence admission decisions. Therefore, CURB-65 should be used alongside clinical judgment rather than as a standalone decision tool.

Reference Ranges