When can pneumonia be treated as outpatient?

PSI Class I–II (low risk): outpatient treatment is generally safe. Class III (moderate risk): brief observation or outpatient with close follow-up. Class IV–V (high risk): inpatient admission recommended. Class V patients should be evaluated for ICU-level care.

What is the 30-day mortality by PSI class?

Risk Class I: 0.1%, Class II: 0.6%, Class III: 2.8%, Class IV: 8.2%, Class V: 29.2%. These estimates are from the original PORT validation cohort (Fine et al., NEJM 1997). Mortality rates may be lower with appropriate antibiotic therapy.

How does PSI/PORT compare to CURB-65?

PSI/PORT and CURB-65 are both validated for community-acquired pneumonia (CAP) severity stratification but have very different complexity profiles. PSI/PORT uses 20 variables (age, sex, nursing home residence, 5 comorbidities, 5 physical exam findings, 7 lab/imaging findings) and takes 3–5 minutes to calculate, requiring blood work and chest X-ray. CURB-65 uses 5 binary criteria and takes under 60 seconds. PSI/PORT is more sensitive for identifying truly low-risk patients (Class I–II, less than 1% mortality), reducing unnecessary hospitalizations. CURB-65 is preferred for rapid bedside triage. Use PSI/PORT when CURB-65 gives borderline results or when time and lab results are available.

What are the PSI/PORT risk classes and their mortality?

PSI/PORT stratifies patients into 5 risk classes: Class I: Age under 50, no comorbidities, normal vitals and mental status — very low risk (under 0.1% mortality), safe for outpatient treatment. Class II: Score 70 or less — low risk (under 0.7% mortality), outpatient treatment appropriate. Class III: Score 71–90 — low-moderate risk (approximately 1–2.8% mortality), consider brief inpatient observation or outpatient with close follow-up. Class IV: Score 91–130 — moderate-high risk (approximately 8–9.3% mortality), hospitalization recommended. Class V: Score above 130 — high risk (approximately 27–29.2% mortality), hospitalization required, consider ICU.

PSI/PORT Score Calculator — Pneumonia Severity Index

About the PSI / PORT Score

The Pneumonia Severity Index (PSI), also known as the PORT Score (Pneumonia Outcomes Research Team), is a validated clinical decision tool for risk-stratifying adults with community-acquired pneumonia (CAP). Published by Fine et al. in the New England Journal of Medicine in 1997, it remains one of the most widely studied and endorsed tools in CAP management.

The PSI was derived from a prospective cohort of 14,199 adults hospitalized with CAP across multiple sites in the United States and Canada, and validated in a separate cohort of 38,039 patients. The derivation methodology used logistic regression to identify patient characteristics independently associated with 30-day mortality, resulting in a weighted point system that reflects the relative contribution of each risk factor to overall mortality. The breadth of input variables — including not just vital signs but demographic, comorbidity, and laboratory data — makes PSI particularly discriminating at the lower end of the severity spectrum, distinguishing patients who are truly at negligible risk from those with borderline risk that may benefit from observation.

The PSI uses a two-step process: a rapid clinical screen identifies the lowest-risk patients (Class I) without any lab work; all others undergo a point-based scoring system incorporating demographics, comorbidities, physical exam findings, and laboratory/imaging results.

How to Use This Calculator

Start by entering the patient's age and selecting their biological sex. If the patient is aged 50 or below with no comorbidities checked and no abnormal vital signs or mental status, the calculator will automatically classify them as Class I — the highest-risk-reduction category — without requiring lab results.

For all other patients, check each criterion that is present. The demographics section captures age (the largest point contributor, with male sex deducting 10 points from the age-based score), and nursing home residence (+10). Comorbidities should reflect active, clinically significant conditions: neoplastic disease means active malignancy excluding basal cell carcinoma; liver disease means cirrhosis or chronic active hepatitis; renal disease means dialysis dependence or baseline creatinine above 1.2 mg/dL. Physical exam findings should reflect the patient's presentation at the time of evaluation. Laboratory values require a full metabolic panel, arterial blood gas if available, and chest imaging. The score breakdown is displayed in the results panel, showing the individual contribution of each component.

Risk Class Classification

Class	Points	30-Day Mortality	Typical Disposition
I	Step 1 screen	0.1%	Outpatient
II	≤70	0.6%	Outpatient
III	71–90	0.9%	Brief observation or inpatient
IV	91–130	9.3%	Inpatient
V	>130	27%	Inpatient (consider ICU)

Step 1: Class I Screening Criteria

A patient qualifies as Class I if all of the following are true:

Age ≤50 years
No active neoplastic disease
No liver disease
No congestive heart failure
No cerebrovascular disease
No renal disease
Normal mental status
Respiratory rate <30/min
Systolic BP ≥90 mmHg
Temperature 35–39.9°C
Pulse <125/min

Class I patients have a 30-day mortality of approximately 0.1% and are appropriate for outpatient management when social circumstances allow.

PSI vs. CURB-65

The PSI and CURB-65 are both validated CAP severity scores recommended by IDSA/ATS guidelines. The PSI is more sensitive for identifying low-risk patients (better at ruling out high severity in young, healthy patients) while CURB-65 is simpler (5 variables, easier to calculate bedside without labs). The 2019 ATS/IDSA guidelines suggest either can be used; many centers use CURB-65 for initial triage and PSI for more nuanced risk stratification.

When to Apply the PSI

The PSI is most useful for:

Identifying CAP patients appropriate for outpatient treatment (Classes I–II)
Supporting ED disposition decisions at the Class II/III boundary
Risk communication with patients and families
Research and quality benchmarking in CAP outcomes

The PSI is not a substitute for clinical judgment. Class III patients represent a grey zone where clinical factors — oxygenation, social support, ability to take oral medications, comorbidity trajectory — should heavily influence the admission decision.

Limitations & Considerations

The PSI was derived and validated in the pre-CAP antibiotic era and may underweight severity in immunocompromised patients (HIV, immunosuppression), aspiration pneumonia, and patients with rapidly progressive illness. It does not incorporate SARS-CoV-2 status, procalcitonin, or lactate. The original validation cohort was predominantly white and older; apply with caution in younger immunocompromised populations.

Age bias: Because age is the largest single point contributor (points = age in years), older patients accumulate high scores even with minimal acute illness severity. A healthy 75-year-old with a mild pneumonia will score as Class IV (75 points from age alone, before any comorbidities or vital signs), potentially leading to over-hospitalization. Clinicians should use clinical judgment alongside the PSI for elderly patients with low acute illness burden.

Immunocompromised patients: The PSI was not derived or validated in populations with HIV/AIDS, solid organ transplant, hematologic malignancy, or high-dose immunosuppressive therapy. These patients are at substantially higher risk of severe and atypical pneumonia (including opportunistic organisms such as Pneumocystis jirovecii) than the PSI score would indicate. PSI should be applied with significant caution or avoided in this population.

Social and logistical factors: The PSI is a medical risk tool and does not account for social factors that affect the safety of outpatient management — ability to take oral medications, access to follow-up care, reliable home monitoring, or caregiver support. A Class II patient with no home support or inability to take oral medications may still require hospitalization.

Not a substitute for clinical judgment: PSI Class III represents a recognized "grey zone" where the evidence base for outpatient versus inpatient management is equivocal. Multiple guidelines recommend that Class III disposition decisions be driven by clinical factors including oxygenation (SpO2 below 92% on room air), fluid tolerance, comorbidity trajectory, and physician judgment — not PSI alone.

References

Fine MJ, et al. A Prediction Rule to Identify Low-Risk Patients with Community-Acquired Pneumonia. N Engl J Med. 1997;336(4):243–250. PMID: 8995086.

Mandell LA, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults. Clin Infect Dis. 2007;44 Suppl 2:S27–72. PMID: 17278083.

Metlay JP, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia: An Official Clinical Practice Guideline of the ATS and IDSA. Am J Respir Crit Care Med. 2019;200(7):e45–e67. PMID: 31573350.

PSI / PORT Score Calculator