PSI is a more detailed pneumonia severity score than CURB-65, using age, coexisting illnesses, exam findings, and lab and imaging results to sort patients into five risk classes for 30-day mortality.
Low risk — outpatient treatment.
Consider a short observation stay.
Higher risk — inpatient.
Highest risk — inpatient, consider ICU.
PSI is more detailed and validated more extensively for mortality prediction, but CURB-65 is faster to calculate at the bedside; many clinicians use CURB-65 for a quick first pass and PSI when more precision is needed.
Class I–II is low risk (outpatient), Class III suggests observation, and Class IV–V is higher risk (inpatient, with ICU consideration for Class V).
Age in years is added straight into the score (minus 10 for women), reflecting how strongly age predicts pneumonia mortality.
Class I isn't purely point-based — it also requires age under 50 with none of the listed comorbidities or vital-sign abnormalities. This tool groups low totals as Class I–II.