PSI Calculator
Pneumonia Severity Index (PORT Score) — Evidence-based risk stratification for community-acquired pneumonia
Demographics
Step 1: Basic patient information
Female sex reduces the score by 10 points, reflecting lower age-adjusted mortality risk
Age in years. Males score +1 point per year; females score +1 per year minus 10 (net effect)
+10 points. Nursing home residence is associated with higher pneumonia severity and mortality risk
Comorbidities
Check all that apply
+30 points. Any malignancy (solid tumor, lymphoma, or leukemia) that is active or was treated within 1 year of presentation
+20 points. Clinical or histologic diagnosis of cirrhosis or chronic active hepatitis
+10 points. Documented systolic or diastolic ventricular dysfunction by history, physical, or imaging
+10 points. Clinical diagnosis of stroke or transient ischemic attack, or cerebrovascular disease on brain imaging
+10 points. History of chronic renal disease or abnormal blood urea nitrogen and creatinine in the medical record
Physical Examination
Findings on current examination
+20 points. Disorientation to person, place, or time not known to be chronic; stupor; or coma
+20 points. Tachypnea defined as 30 or more breaths per minute at the time of initial evaluation
+20 points. Hypotension indicating potential hemodynamic instability and higher disease severity
+15 points. Core temperature below 35°C (95°F) or above 39.9°C (103.8°F) indicating hypothermia or high-grade fever
+10 points. Tachycardia suggesting systemic inflammatory response and cardiovascular stress
Laboratory & Radiology
Results from current workup
+30 points. Acidemia indicates severe physiologic compromise and is the single strongest laboratory predictor of mortality
+20 points. Elevated blood urea nitrogen (azotemia) reflecting renal hypoperfusion, dehydration, or pre-existing renal disease
+20 points. Hyponatremia associated with syndrome of inappropriate ADH secretion (SIADH) in pneumonia
+10 points. Hyperglycemia reflecting stress response and associated with worse pneumonia outcomes
+10 points. Anemia defined as hematocrit below 30%, reducing oxygen-carrying capacity and tissue oxygen delivery
+10 points. Hypoxemia on pulse oximetry, accepted as equivalent alternative when ABG is not available
+10 points. Parapneumonic effusion on chest radiograph indicating complicated pneumonia course
Calculate PSI Score
Enter patient age and sex, then check all applicable comorbidities, physical exam findings, and laboratory results to calculate the Pneumonia Severity Index.
How to Use the PSI Calculator
Enter Demographics
Input the patient's age in years and select biological sex. For females, the PSI automatically subtracts 10 points from the age contribution to account for lower age-adjusted mortality risk. Check if the patient is a nursing home resident (+10 points). These demographics form the foundation of the Step 1 Class I auto-assignment check.
Check Comorbid Conditions
Select all applicable comorbidities from the list: neoplastic disease (+30), liver disease (+20), congestive heart failure (+10), cerebrovascular disease (+10), and renal disease (+10). If the patient is 50 or younger AND no comorbidities are present AND no abnormal vital signs — the system will automatically assign Class I without requiring laboratory values.
Record Physical Exam and Labs
Check any abnormal findings on physical examination: altered mental status (+20), respiratory rate 30 or more per minute (+20), systolic BP below 90 mmHg (+20), abnormal temperature (+15), and pulse 125 or more bpm (+10). Then enter applicable laboratory findings including arterial pH, BUN, sodium, glucose, hematocrit, oxygenation (choose PaO2 or SpO2), and pleural effusion on X-ray.
Review Risk Class and Disposition
After calculating, review the total PSI score, risk class (I-V), 30-day mortality rate, and evidence-based disposition recommendation. The visual score breakdown chart shows the contribution from each input category. Always integrate the PSI result with clinical judgment, patient-specific social and functional factors, and local resources before making a final disposition decision.
Frequently Asked Questions
What is the PSI/PORT Score and who developed it?
The Pneumonia Severity Index (PSI), also known as the PORT Score (Patient Outcomes Research Team), is a validated clinical prediction rule developed by Michael Fine and colleagues, published in the New England Journal of Medicine in 1997 (volume 336, pages 243-250). It was derived from 14,199 hospitalized patients with community-acquired pneumonia (CAP) across five teaching hospitals and subsequently validated on over 38,000 additional patients. The PSI assigns patients to one of five risk classes based on 20 variables covering demographics, comorbid conditions, physical examination findings, and laboratory and radiographic data. The American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) include it in their CAP management guidelines as the preferred severity scoring system.
Why might a young patient with severe pneumonia have a low PSI score?
This is the most important clinical limitation of the PSI. Because age contributes directly to the point score (one point per year for males), a 25-year-old male starts with only 25 base points. Even with several positive findings like tachypnea (+20), hypotension (+20), and low arterial pH (+30), the total score could still fall in Class III or lower. This age bias means the PSI can systematically underestimate severity in younger patients who are truly physiologically compromised. Clinicians should always override the PSI when clinical presentation suggests severity that the score doesn't capture. Some experts recommend using clinical parameters like ARDS criteria, septic shock, or bilateral involvement to supplement PSI in young patients.
What is the difference between PSI Class I and Class II, and why does Class I not require a point score?
Class I is a special auto-assigned category for patients who meet all three Step 1 criteria simultaneously: age 50 years or younger, no comorbid conditions (no neoplastic disease, liver disease, CHF, cerebrovascular disease, or renal disease), and no abnormal vital signs (no altered mental status, respiratory rate below 30, systolic BP 90 or above, temperature 35 to 39.9 degrees Celsius, and pulse below 125 bpm). These patients have demonstrated very low mortality risk regardless of laboratory values, so Step 2 point scoring is not needed. Class II covers patients who either do not meet Step 1 criteria or are older than 50, with a calculated point score of 70 or less. Both classes support outpatient management, but Class II requires that a score calculation confirm the low-risk designation.
Is SpO2 an acceptable substitute for PaO2 in the PSI calculation?
Yes. The oxygenation criterion in the PSI was originally defined as PaO2 below 60 mmHg on arterial blood gas (ABG). However, because ABG may not always be immediately available or clinically indicated, an SpO2 below 90% on pulse oximetry is widely accepted as a clinically equivalent alternative for PSI scoring purposes. This is supported by multiple implementations including EBMCalc, IMPACT, and several academic medical center calculators. When ABG is available, use PaO2; when it is not, SpO2 below 90% is the appropriate substitute. Note that the two measurements can occasionally diverge in patients with hemoglobin abnormalities such as methemoglobinemia or carbon monoxide exposure, where SpO2 may be falsely normal.
When should I use PSI versus CURB-65 for pneumonia severity assessment?
Both scores have specific strengths. The PSI excels at identifying patients who are safe for outpatient discharge — it has higher sensitivity for identifying low-risk patients, which means fewer false positives for admission. The ATS and IDSA 2019 guidelines prefer the PSI over CURB-65 for this reason. CURB-65 (Confusion, Urea, Respiratory rate, Blood pressure, age 65 or over) uses only 5 variables, making it faster and feasible when laboratory results are unavailable. CURB-65 has higher specificity for predicting mortality (74.6% vs 52.2% for PSI), meaning fewer healthy patients are falsely flagged as high risk. A practical approach: use the PSI as the primary tool when full laboratory data is available and you are considering outpatient discharge; use CURB-65 as a rapid bedside screen or when lab data is delayed. Importantly, they should supplement, not replace, clinical judgment.
What disposition is appropriate for PSI Class III patients?
Class III (score 71-90 points) represents a low-moderate risk group with a 30-day mortality of 0.9 to 2.8% — meaningfully higher than Class I-II but far below Class IV-V. The evidence does not mandate hospitalization for Class III, and many patients are appropriately managed as outpatients. The preferred approach depends on individual patient factors: if the patient can reliably take oral antibiotics, has adequate home support, no functional limitations, can follow up within 24 hours, and has no concerning social factors, outpatient management is reasonable with careful arrangement of next-day follow-up. If any of these conditions are not met — inability to tolerate oral medications, unreliable follow-up, significant comorbidities not fully captured by the score, or clinician concern — a brief observation admission (24 hours) or short-stay unit placement is appropriate.