Pneumonia Severity Scoring: CURB-65 and PSI
Use CURB-65 as your primary severity scoring tool for pneumonia due to its simplicity, ease of recall, and effectiveness in predicting mortality and guiding site-of-care decisions. 1
CURB-65 Score Components
The CURB-65 score assigns one point for each of the following five criteria 1, 2:
- Confusion (based on mental test or disorientation to person, place, or time)
- Urea >7 mmol/L (or BUN >20 mg/dL)
- Respiratory rate ≥30 breaths/min
- Blood pressure (systolic <90 mmHg or diastolic ≤60 mmHg)
- Age ≥65 years
Risk Stratification and Management
The mortality risk increases dramatically with higher CURB-65 scores, directly guiding your admission decisions 1:
- Score 0-1: 0.7-2.1% mortality → Consider outpatient treatment 1, 2, 3
- Score 2: 9.2% mortality → Consider hospital admission or intensive outpatient care 1, 2
- Score ≥3: 14.5-57% mortality → Hospitalize and assess for ICU admission 1, 2
Alternative: CRB-65 for Primary Care
Use CRB-65 (omitting the urea measurement) in outpatient settings where laboratory testing is unavailable, maintaining a 0-4 point scale with similar risk stratification 1, 2
When to Use PSI Instead
Consider the Pneumonia Severity Index (PSI) in emergency departments with computerized decision support, as it incorporates 20 variables and may identify slightly more low-risk patients suitable for outpatient management 1, 4. However, PSI's complexity limits bedside practicality 1.
The PSI stratifies patients into five risk classes with mortality rates: Classes I-III (≤3%), Class IV (8%), and Class V (35%) 4, 3.
Critical Limitations Requiring Clinical Override
Never rely solely on scoring tools—they must be supplemented with clinical judgment 1:
Situations requiring admission despite low scores:
- Hypoxemia: SpO2 <90% or PaO2 <60 mmHg 1
- Shock or hemodynamic instability requiring vasopressors 1
- Acute respiratory failure requiring intubation 1
- Complications: Pleural effusion, empyema 1
- Exacerbation of comorbidities: COPD, heart failure, diabetes 1
- Inability to take oral medications or maintain hydration 1
- Social factors: Homelessness, no caregiver, psychiatric illness, substance abuse 1
- Failed outpatient therapy 1
Situations where scores may underestimate severity:
- Young patients with severe respiratory failure (CURB-65 underestimates due to age <65) 2, 3
- Elderly patients with multiple stable comorbidities (PSI may overestimate based on age alone) 1
ICU Admission Criteria
For ICU triage, use the IDSA/ATS severe CAP criteria rather than CURB-65 alone, as CURB-65 performs poorly for predicting ICU needs 4, 2, 3:
Major criteria (either one requires ICU):
- Septic shock requiring vasopressors 1, 2
- Acute respiratory failure requiring intubation and mechanical ventilation 1, 2
Minor criteria (≥3 require ICU):
- Respiratory rate ≥30/min
- PaO2/FiO2 ratio ≤250
- Multilobar infiltrates
- Confusion/disorientation
- Uremia (BUN ≥20 mg/dL)
- Leukopenia (WBC <4,000)
- Thrombocytopenia (platelets <100,000)
- Hypothermia (core temperature <36°C)
- Hypotension requiring aggressive fluid resuscitation 4, 2
Practical Implementation
CURB-65 is preferred over PSI because it requires only 5 easily remembered variables versus 20, making it practical at the bedside without calculation sheets 1. The score can be calculated in seconds during initial assessment 1, 3.
Reassess patients dynamically over several hours rather than relying on a single time-point score, as vital signs and mental status may fluctuate 1.