Pneumonia Severity Index (PSI)
Helps determine risk of mortality from Community-Acquired Pneumonia (CAP) and guides home vs. admit; PSI is favored over CURB-65 by ATS/IDSA but is cumbersome to use, resulting in many preferring CURB-65.
Original author(s)
Michael J. Fine and the Pneumonia Patient Outcomes Research Team (PORT) investigators. Placeholder — verify authorship/affiliations
Original study
Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243–250. Derived on 14,199 inpatients and validated on 38,039 patients across the PORT cohort. Placeholder — verify PMID + exact figures
Validating studies
Externally validated across multiple cohorts and compared head-to-head with CURB-65 (e.g., Aujesky et al., Am J Med 2005, found PSI slightly more discriminating for mortality). Placeholder — pick the citations we want to stand behind
When to use
Adults with radiographically confirmed CAP, to risk-stratify 30-day mortality and support the outpatient-vs-admit decision. Its real strength is confidently identifying the low-risk patient who is safe to treat at home. Placeholder — red-pen
When NOT to use
Not validated in immunocompromised hosts. It is a mortality predictor, not a disposition rule — a low score does not capture hypoxia in a young patient, inability to tolerate PO, or absent home support; those override the number. Not for hospital-acquired pneumonia. Placeholder — red-pen
Our take — why check the score here
Where we go past a bare calculator: our opinion on PSI vs. CURB-65 in a real ED, the traps in Class I, and a one-tap jump to our CAP treatment page once you have a disposition. Placeholder — this is the section that beats MDCalc; red-pen the voice