Pneumonia Severity Index Calculator (PSI / PORT score, Fine 1997)

Understanding the Pneumonia Severity Index calculator — concept and principle

The Pneumonia Severity Index (PSI), also called the PORT score, sorts adults with community-acquired pneumonia into five risk classes for death within 30 days. Doctors use it, together with clinical judgement, to decide whether a patient can be treated at home or needs hospital care.

Age plus findings: with the default inputs the result is 122 → Class IV (inpatient care).

How it is calculated

Step 1: a patient aged 50 or younger with none of five illnesses (cancer, liver disease, heart failure, cerebrovascular disease, kidney disease) and none of five examination findings (confusion, breathing 30/min or more, systolic under 90 mmHg, temperature under 35 °C or 40 °C or more, pulse 125/min or more) is class I.

Step 2: everyone else is scored:

Age in years (women: age − 10); nursing-home resident +10
Cancer +30; liver disease +20; heart failure, cerebrovascular disease, kidney disease +10 each
Confusion, breathing rate 30 or more, systolic under 90 +20 each; abnormal temperature +15; pulse 125 or more +10
pH under 7.35 +30; BUN 30 mg/dL or more and sodium under 130 +20 each; glucose 250 mg/dL or more, haematocrit under 30%, PaO₂ under 60 mmHg, pleural effusion +10 each

Class II ≤ 70, III 71–90, IV 91–130, V > 130.

The principle

Fine and colleagues (1997) derived the rule in more than 14,000 patients and validated it in over 38,000. Age is the backbone of the score, and each additional illness, abnormal sign or test result adds points in proportion to how strongly it predicted death.

Worked example

Default inputs: male, 72, heart failure, breathing rate 30 or more, BUN 30 or more; everything else no.

Age = 72 points (male).
Heart failure +10; breathing rate +20; BUN +20.
Total = 72 + 10 + 20 + 20 = 122.
91–130 → Class IV; 30-day mortality in the PORT cohort 9.3% (range 8.2–9.3%) → Inpatient care.

How to read the result

Where does your result fall?

Classes I–II are usually suitable for outpatient care, class III for outpatient care or brief observation, and IV–V for hospital admission. The score supports but does not replace clinical judgement: low oxygen, inability to take medicines, social circumstances and other conditions may still justify admission.

Common mistakes

Skipping step 1 for young, otherwise healthy patients.
Forgetting to subtract 10 for women.
Using the score for hospital-acquired pneumonia.

Keep in mind: This is a decision aid for clinicians, not a diagnosis. Anyone with breathing difficulty, confusion or chest pain needs urgent medical care.

Frequently asked questions

What is the difference between PSI and CURB-65?

CURB-65 uses five simple items and is quicker; PSI uses more information and is better at identifying low-risk patients.

Why does age count so much?

Older age was the strongest single predictor of death in the derivation data.

Can a young patient be class IV?

Yes, if they have several serious abnormal findings.

Sources: 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

Checked 9 Nov 2026. 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 — Figure 1 (step 1), Table 2 (points) and Table 3 (mortality by class: MedisGroups derivation and validation, PORT validation cohort).

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