Risk Classification in Community-Acquired Pneumonia
Use CURB-65 for rapid bedside risk stratification in community-acquired pneumonia, as it requires only 5 simple variables and effectively guides site-of-care decisions, while PSI remains superior for identifying truly low-risk patients who can be safely discharged home. 1, 2
CURB-65 Score Calculation
Award 1 point for each of the following:
- Confusion (new disorientation to person, place, or time)
- Urea >7 mmol/L (or BUN >19 mg/dL)
- Respiratory rate ≥30 breaths/min
- Blood pressure: systolic <90 mmHg OR diastolic ≤60 mmHg
- Age ≥65 years
Risk Stratification by CURB-65 Score:
- Score 0-1: Low risk (0.7-3.2% mortality) → Outpatient treatment
- Score 2: Intermediate risk (9.2% mortality) → Consider short hospital stay or supervised outpatient care
- Score 3-5: High risk (14.5-57% mortality) → Hospitalize and assess for ICU admission 1
The mortality increases dramatically with each point: 0.7% (score 0), 2.1% (score 1), 9.2% (score 2), 14.5% (score 3), 40% (score 4), and 57% (score 5) 1.
Pneumonia Severity Index (PSI)
The PSI uses up to 20 variables including age, comorbidities (renal, heart, liver disease, malignancy), vital signs, and laboratory/radiographic findings. It stratifies patients into 5 risk classes:
- Classes I-III: ≤3% mortality → Safe for outpatient treatment
- Class IV: 8% mortality → Hospitalization recommended
- Class V: 35% mortality → Hospitalization with ICU consideration 1, 2
Comparative Performance:
PSI advantages: Higher discriminatory power (AUC 0.81 vs 0.73-0.76 for CURB-65), identifies more patients as low-risk (68% vs 51-61%), and has superior sensitivity for predicting mortality 3. The PSI is the preferred tool per IDSA guidelines for determining outpatient eligibility 4.
CURB-65 advantages: Simpler calculation requiring only 5 variables versus 20, no need for laboratory tests beyond urea, and easier point-of-care application 1, 2. British Thoracic Society guidelines endorse CURB-65 as the primary tool 2.
Critical Pitfalls and Limitations
PSI underestimates severity in:
- Young patients without comorbidities who develop severe respiratory failure (hypoxia alone doesn't score highly enough)
- Does NOT include COPD or diabetes as risk factors despite their clinical importance 1
CURB-65 underestimates severity in:
- Elderly patients with multiple comorbidities
- Patients requiring ICU admission who don't meet the score thresholds 1
Practical Algorithm for Clinical Use
- Calculate CURB-65 first at initial presentation (faster, requires minimal testing)
- If CURB-65 = 0-1: Consider outpatient treatment if no concerning features
- If CURB-65 = 2: Exercise clinical judgment; calculate PSI if available to refine decision
- If CURB-65 ≥3: Hospitalize and assess for ICU criteria
When to Override the Scores:
Both tools support but do not replace clinical judgment 2. Consider hospitalization despite low scores when:
- HIV or other immunocompromising conditions
- Failed outpatient antibiotic therapy
- Inability to reliably take medications or obtain care
- Significant hypoxemia (oxygen saturation concerns)
- Social factors preventing safe home care 2
CRB-65 Alternative
When blood urea testing is unavailable, use CRB-65 (omits urea, scored 0-4). This maintains utility for initial triage, particularly in resource-limited settings or remote assessments 2, 5.
Score interpretation:
- 0 = <1% mortality risk
- 1-2 = 1-10% mortality risk
- 3-4 = >10% mortality risk 5
ICU Admission Criteria
For patients requiring hospitalization, IDSA/ATS criteria identify those needing ICU-level care:
Major criteria (either one = ICU admission):
- Invasive mechanical ventilation required
- Septic shock requiring vasopressors
Minor criteria (≥3 present = ICU admission):
- Respiratory rate ≥30/min
- PaO2/FiO2 ratio ≤250
- Multilobar infiltrates
- Confusion
- Uremia (BUN ≥20 mg/dL)
- Leukopenia (WBC <4000)
- Thrombocytopenia (platelets <100,000)
- Hypothermia (core temperature <36°C)
- Hypotension requiring aggressive fluid resuscitation 1