What is CURB-65 (Confusion, Urea, Respiratory rate, Blood pressure, and 65 years of age)?

CURB-65: A Clinical Severity Score for Community-Acquired Pneumonia

CURB-65 is a validated 5-variable clinical prediction tool that stratifies community-acquired pneumonia patients by mortality risk to guide hospitalization decisions, with each letter representing one point: Confusion, Urea >7 mmol/L (BUN >19 mg/dL), Respiratory rate ≥30/min, Blood pressure (systolic <90 or diastolic ≤60 mmHg), and age ≥65 years. 1

Scoring Components

Each of the following clinical parameters receives 1 point, creating a score ranging from 0 to 5: 2, 1

• Confusion (new onset disorientation)
• Urea nitrogen >7 mmol/L (or BUN >19 mg/dL)
• Respiratory rate ≥30 breaths per minute
• Blood pressure: systolic <90 mmHg or diastolic ≤60 mmHg
• 65 years of age or older

Risk Stratification and Mortality Prediction

The score directly correlates with 30-day mortality risk: 1, 3

• Score 0-1: 0.7-2.1% mortality risk → Consider outpatient treatment
• Score 2: 9.2% mortality risk → Consider short hospital stay or supervised outpatient treatment
• Score 3: 14.5% mortality risk → Hospital admission and ICU assessment
• Score 4-5: 40-57% mortality risk → Hospital admission and ICU assessment

The mortality rates have been validated across multiple cohorts, with one large European study demonstrating 30-day mortality of 1.1%, 7.6%, 21%, 41.9%, and 60% for scores of 0,1,2,3,4, and 5 respectively. 3

Clinical Application and Site-of-Care Decisions

The American Thoracic Society and British Thoracic Society recommend using CURB-65 as a validated clinical decision rule to support clinical judgment for determining hospitalization needs in community-acquired pneumonia. 2, 1

Treatment Recommendations by Score:

• CURB-65 ≤1: Outpatient treatment is generally safe 1
• CURB-65 = 2: Clinical judgment is particularly important in this intermediate-risk group; consider patient-specific factors 1
• CURB-65 ≥3: Hospitalization required with prompt evaluation for ICU admission 1

Practical Advantages

CURB-65 offers several clinical benefits over more complex scoring systems: 2, 1

• Simplicity: Uses only 5 variables compared to 20 in the Pneumonia Severity Index (PSI)
• Point-of-care accessibility: Easy to calculate and interpret in emergency settings
• Minimal testing: Requires only one laboratory test (urea/BUN) that is readily available
• Efficiency: Helps reduce unnecessary hospitalizations while ensuring appropriate care for high-risk patients

CRB-65: The Simplified Alternative

A variant called CRB-65 omits the urea nitrogen measurement, creating a 0-4 point scale that can be used when laboratory testing is not immediately available. 2, 1 This is particularly useful in outpatient settings, resource-limited environments, or when rapid assessment is needed before blood work returns. 1

Important Limitations and Clinical Caveats

When CURB-65 May Underestimate Severity:

Young patients with severe respiratory failure: The score may underestimate severity in previously healthy patients under 65 years with significant physiologic derangement, as age is a major component. 1, 4 In one study, 15.6% of patients with CURB-65 scores of 0-1 were admitted to the ICU and 6.4% received critical care interventions. 4

Elderly patients with comorbidities: The score may not fully capture risk in patients with multiple comorbidities not included in the calculation. 1

ICU Admission Decisions:

CURB-65 performs poorly for predicting ICU needs and should not be used as the primary tool for ICU triage decisions. 1 Instead, use the IDSA/ATS severe CAP criteria, which include: 1

• Major criteria (requiring direct ICU admission): Septic shock requiring vasopressors OR acute respiratory failure requiring intubation
• Minor criteria: ≥3 minor criteria warrant ICU consideration

Factors Requiring Clinical Override:

The guidelines emphasize that CURB-65 should support, not replace, clinical judgment. Consider these factors that may necessitate admission despite low scores: 2, 1

• Important comorbidities not captured (HIV, immunosuppression)
• Failure of outpatient oral antibiotic therapy
• Social factors: homelessness, psychiatric illness, inability to obtain or reliably take medications, lack of social support
• Comorbidity exacerbations requiring hospitalization independent of pneumonia severity
• Need for procedures (pleural effusion drainage, supplemental oxygen)

Comparison with PSI

While both tools are validated, they serve slightly different purposes: 1, 5

• PSI: More complex (20 variables), primarily designed to identify low-risk patients for outpatient treatment
• CURB-65: Simpler (5 variables), focuses on illness severity across the full risk spectrum
• Discriminatory power: Recent comparative studies show PSI-HR (modified PSI) has slightly better discrimination (AUROC 0.82) than CURB-65 (AUROC 0.77), though CURB-65 remains highly effective (AUROC 0.73-0.77) 4, 5

Implementation Best Practices

Use CURB-65 as part of a systematic approach to pneumonia severity assessment, always combined with clinical judgment. 1 For patients with CURB-65 scores ≥2, hospitalize or provide intensive in-home health care services, as they face significantly elevated mortality risk requiring active intervention. 1 Patients should be instructed to contact their physician if no clinical improvement occurs within 3 days. 1