What is the Pneumonia Severity Index (PSI) (also known as the PORT score)?

PSI/PORT Scoring System for Community-Acquired Pneumonia

The Pneumonia Severity Index (PSI), also known as the PORT score, is a validated clinical prediction rule that stratifies adult patients with community-acquired pneumonia into five mortality risk classes (I-V) using 20 clinical variables to guide initial site-of-care decisions and treatment intensity. 1

Development and Validation

The PSI was developed by the Pneumonia Patient Outcomes Research Team (PORT) using a derivation cohort of 14,199 hospitalized CAP patients and validated in 38,039 inpatients plus 2,287 combined inpatients and outpatients. 1 This methodologically sound prediction rule quantifies short-term (30-day) mortality risk and has been independently validated in multiple European and international cohorts. 2

Two-Step Stratification Process

Step 1: Risk Class I Identification

Patients are classified as Risk Class I (lowest severity) if they meet ALL of the following criteria: 1

• Age <50 years
• Absence of all 5 major comorbid conditions:
  • Neoplastic disease
  • Liver disease
  • Congestive heart failure
  • Cerebrovascular disease
  • Renal disease
• Normal or only mildly deranged vital signs
• Normal mental status

Step 2: Point-Based Classification (Classes II-V)

All patients not meeting Risk Class I criteria are scored using 20 variables across multiple categories: 1

Demographics:

• Age in years for males (subtract 10 for females)
• Nursing home residence: +10 points

Comorbidities:

• Neoplastic disease: +30 points
• Liver disease: +20 points
• Congestive heart failure: +10 points
• Cerebrovascular disease: +10 points
• Renal disease: +10 points

Physical Examination Findings:

• Mental confusion: +20 points
• Respiratory rate ≥30/min: +20 points
• Systolic blood pressure <90 mmHg: +20 points
• Temperature <35°C or ≥40°C: +15 points
• Heart rate ≥125 bpm: +10 points

Laboratory/Radiographic Findings:

• Arterial pH <7.35: +30 points
• Blood urea nitrogen >11 mmol/L (>30 mg/dL): +20 points
• Sodium <130 mmol/L: +20 points
• Glucose >250 mg/dL: +10 points
• Hematocrit <30%: +10 points
• PaO₂ <60 mmHg or O₂ saturation <90%: +10 points
• Pleural effusion on chest X-ray: +10 points

Risk Class Assignment by Total Points: 1

• Class II: <70 points
• Class III: 71-90 points
• Class IV: 91-130 points
• Class V: >130 points

Mortality Risk by Risk Class

The validated 30-day mortality rates are: 1

• Class I: 0.1-0.4%
• Class II: 0.6-0.7%
• Class III: 0.9-2.8%
• Class IV: 8.2-9.3%
• Class V: 27.0-31.1%

Clinical Application for Site-of-Care Decisions

Outpatient Management: Classes I-II patients can be safely treated as outpatients, with mortality risk ≤3% when combined with Class III. 1

Observation or Brief Hospitalization: Class III patients are potential candidates for brief inpatient observation or supervised outpatient care. 1

Traditional Inpatient Care: Classes IV-V patients require hospital admission. 1

ICU Consideration: The PSI was not specifically designed to predict ICU need, but higher risk classes (IV-V) correlate with increased ICU admission rates. 1

Clinical Impact and Utility

The PSI has been shown to reduce avoidable hospital admissions and length of stay, thereby decreasing overall healthcare costs, though no impact on mortality reduction has been demonstrated. 1 Studies suggest that using PSI could reduce traditional inpatient care by approximately 31%. 1

Important Limitations and Caveats

Age Bias: Increasing age is a dominant determinant in the scoring system, which may lead to underestimation of pneumonia severity in younger patients without comorbidities who develop severe respiratory failure. 1

Complexity: The score requires 20 variables including laboratory tests, blood gas analysis, and chest radiography, making bedside calculation cumbersome and necessitating additional testing. 1

Mortality Focus: The PSI classifies risk of death, not all reasons for hospitalization. Patients may require admission for supplemental oxygen, pleural drainage, or inability to take oral medications despite low PSI scores. 1

Not a Substitute for Clinical Judgment: The PSI should serve as an adjunct to, not a replacement for, clinical judgment. Non-clinical factors (social support, ability to follow-up, medication access) may justify hospitalization in selected low-risk cases. 1

Hypoxemia Consideration: If the strategy is amended to include hospitalization for any patient with arterial hypoxemia (PaO₂ <60 mmHg or O₂ saturation <90%) regardless of PSI class, the reduction in inappropriate outpatient management is improved. 1

Comparison to Alternative Scoring Systems

The PSI demonstrates comparable mortality prediction to the simpler CURB-65 score, though CURB-65 requires only 5 variables and can be calculated more rapidly at the bedside. 1 The 2007 IDSA/ATS guidelines provide a strong recommendation for using severity-of-illness scores like PSI or CURB-65 to identify outpatient candidates. 1