PSI / PORT Score Calculator
Pneumonia Severity Index — stratifies community-acquired pneumonia into five risk classes (I–V) using demographics, comorbidities, vital signs, and laboratory findings. Guides disposition from outpatient management to ICU admission based on estimated 30-day mortality.
Calculate PSI / PORT Score
The PSI uses a two-step algorithm. Step 1 identifies low-risk patients (Risk Class I) who may not need laboratory testing. If any Step 1 disqualifier is present, Step 2 calculates the full point score using demographics, comorbidities, vitals, and laboratory values to assign Risk Classes II–V.
STEP 2 — LABORATORY & IMAGING (if not Class I)
The PSI/PORT score was validated for community-acquired pneumonia in immunocompetent adults. It estimates 30-day all-cause mortality but does not assess the need for ICU-level care. Patients in lower risk classes may still require admission for non-mortality reasons — inability to take oral medications, unstable comorbidities, homelessness, or active substance use. Clinical judgement must complement the score.
Understanding the PSI / PORT Score
The Pneumonia Severity Index was developed in 1997 by Fine and colleagues as part of the Pneumonia Patient Outcomes Research Team (PORT) study. It was derived from a cohort of 14,199 hospitalised patients with CAP and validated in a prospective cohort of 2,287 patients across multiple centres. The PSI remains one of the most extensively validated tools in pneumonia risk assessment, with over 40 validation studies across diverse populations.
The score uses a two-step algorithm. Step 1 is a rapid screen that identifies patients eligible for Risk Class I (lowest mortality) without any laboratory testing — patients age ≤ 50 with no comorbidities and no vital sign abnormalities are classified as Class I. If any of these criteria are present, Step 2 assigns a point score based on 20 variables spanning demographics, comorbidities, physical examination, and laboratory/imaging findings. The point total determines Risk Classes II through V.
Point Allocation Summary
Demographics:
Male: age in years
Female: age − 10
Nursing home: +10
Comorbidities:
Neoplastic: +30
Liver disease: +20
CHF / CVD / Renal: +10 each
Highest-weighted labs:
pH < 7.35: +30
BUN ≥ 30 / Na < 130: +20 each
Class I Eligibility (Step 1)
All of the following must be true:
✓ Age ≤ 50 years
✓ No neoplastic disease
✓ No liver disease
✓ No heart failure
✓ No cerebrovascular disease
✓ No renal disease
✓ No altered mental status
✓ Pulse < 125/min
✓ RR < 30/min
✓ SBP ≥ 90 mmHg
✓ Temp 35–39.9°C
30-day mortality: 0.1%
The PSI was designed to identify low-risk patients safe for outpatient treatment. Its primary purpose is to prevent unnecessary hospitalisation for low-severity pneumonia — not to determine who needs ICU admission. For ICU triage, the ATS/IDSA severe pneumonia criteria or tools like the SMART-COP score are more appropriate. The PSI excels at identifying Classes I–III patients who can be safely managed in the outpatient setting.
Risk Classes & Mortality Estimates
| Risk Class | Point Score | 30-Day Mortality | Recommended Disposition |
|---|---|---|---|
| I | Step 1 algorithm | 0.1% | Outpatient |
| II | ≤ 70 | 0.6% | Outpatient |
| III | 71–90 | 0.9–2.8% | Brief inpatient or outpatient with close follow-up |
| IV | 91–130 | 8.2–9.3% | Inpatient |
| V | > 130 | 27.0–31.1% | Inpatient — consider ICU |
Classes I and II together account for ~60% of all CAP patients — and the original PORT study demonstrated that these patients can be safely managed as outpatients, potentially reducing unnecessary hospitalisations by 25–30%. The key contribution of the PSI is giving clinicians the confidence to send home patients who look unwell but have an objectively low mortality risk.
Disposition Guidance by Risk Class
Clinical Management by PSI Risk Class
Patients in PSI Classes I and II are appropriate for outpatient management with oral antibiotics. The mortality rate is below 1%, comparable to the background risk of hospitalisation-related adverse events. The original PORT randomised trial demonstrated that outpatient management for low-risk patients was safe and reduced healthcare costs by approximately 50% without increasing adverse outcomes.
ATS/IDSA guidelines (2019): Amoxicillin 1 g TDS (preferred), OR doxycycline 100 mg BD, OR a macrolide (azithromycin 500 mg day 1 then 250 mg days 2–5) in areas with pneumococcal macrolide resistance < 25%. If comorbidities are present (chronic heart, lung, liver, or renal disease, diabetes, alcoholism, malignancy, asplenia): amoxicillin-clavulanate 875/125 mg BD OR cephalosporin PLUS macrolide, OR respiratory fluoroquinolone monotherapy (levofloxacin 750 mg OD or moxifloxacin 400 mg OD).
- Duration: 5 days is typically sufficient; patient should be afebrile for ≥ 48 hours before stopping
- Follow-up: Clinical review within 48–72 hours; chest radiograph at 6–12 weeks if ≥ 50 years old
- Safety-netting: Return if no improvement by day 3, new or worsening dyspnoea, inability to keep fluids down, or new confusion
Class IV and V patients require hospital admission with intravenous antibiotics. For non-ICU inpatients, ATS/IDSA guidelines recommend a beta-lactam (ceftriaxone 1–2 g IV OD, cefotaxime 1–2 g IV q8h, or ampicillin-sulbactam 1.5–3 g IV q6h) PLUS a macrolide (azithromycin 500 mg IV/PO OD), OR respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV OD).
For patients meeting ATS/IDSA severe CAP criteria (one major criterion: mechanical ventilation or vasopressors; OR ≥ 3 minor criteria: RR ≥ 30, PaO₂/FiO₂ ≤ 250, multilobar infiltrates, confusion, BUN ≥ 20, WBC < 4,000, platelets < 100,000, hypothermia, hypotension requiring fluid resuscitation), ICU admission should be arranged. ICU empirical therapy broadens to include MRSA cover (vancomycin or linezolid) if risk factors are present, and anti-pseudomonal cover if structural lung disease or recent hospitalisation are present.
- Blood cultures: Before antibiotics in all hospitalised patients; positive in ~10–15% of CAP
- Urinary antigens: Pneumococcal and Legionella antigens for all severe CAP
- Corticosteroids: Dexamethasone 6 mg IV daily for 4 days may reduce mortality in hospitalised CAP (CAPE-COD trial)
- IV-to-oral switch: When afebrile for 24 hours, haemodynamically stable, tolerating oral intake, and clinically improving
While the microbial aetiology of CAP does not change dramatically across PSI classes, the likelihood of identifying a pathogen increases with severity (bloodstream infection is rare in Classes I–II but occurs in ~10–15% of Class V). Streptococcus pneumoniae remains the most common identified pathogen across all classes. However, more resistant or aggressive organisms become proportionally more common in higher classes.
In Class IV–V patients, consider expanded coverage for Staphylococcus aureus (including MRSA if risk factors: recent influenza, injection drug use, prior MRSA colonisation), Pseudomonas aeruginosa (if structural lung disease, recent broad-spectrum antibiotics, or recent hospitalisation), and Legionella pneumophila (particularly if hyponatraemia, diarrhoea, or recent travel). Viral aetiologies (influenza, SARS-CoV-2) should be tested and treated with antivirals when appropriate, as co-infection with bacteria occurs in approximately 20–30% of viral pneumonia cases.
Special Populations & Considerations
The PSI does not capture social determinants of health. Patients with homelessness, active substance use, inability to reliably take oral medications, or lack of follow-up access may need hospitalisation regardless of PSI class. The score estimates mortality risk — the disposition decision must also consider the feasibility of safe outpatient management.
PSI vs CURB-65: Choosing the Right Tool
The PSI and CURB-65 are the two most widely validated severity scores for community-acquired pneumonia. Both are endorsed by ATS/IDSA and BTS guidelines. Understanding their relative strengths helps clinicians select the most appropriate tool for the clinical context.
| Feature | PSI / PORT | CURB-65 |
|---|---|---|
| Variables | 20 (demographics, comorbidities, vitals, labs, imaging) | 5 (Confusion, Urea, RR, BP, Age) |
| Risk classes | 5 classes (I–V) | 3 groups (0–1, 2, 3–5) |
| Bedside use | Requires labs and CXR for full scoring | Requires only urea; CRB-65 needs no labs |
| Strength | Excellent at identifying low-risk patients for outpatient care | Simpler; quicker at bedside; good for triage |
| Weakness | May underscore severe disease in young patients; complex | May oversimplify; lacks comorbidity and lab data |
| Age weighting | Heavy (up to 120 points in elderly) | Moderate (1 point if ≥ 65) |
| Best for | Confident outpatient discharge of low-risk patients | Rapid triage; primary care assessment |
| Validated populations | 40+ validation studies worldwide | Multiple; originally UK, NZ, Netherlands |
Use CURB-65 for rapid triage when speed matters and laboratory results are not yet available — it gives an immediate sense of severity with five bedside variables. Use the PSI when the disposition decision is uncertain — particularly when you want to identify patients who can be safely sent home. The PSI’s strength is giving clinicians the confidence to avoid unnecessary admissions in Classes I–II. Many institutions use CURB-65 at the front door and calculate PSI when the labs return to finalise the disposition decision.
Common Pitfalls & Limitations
The PSI’s heavy weighting of age means young patients start with fewer points and may be classified as low-risk despite severe disease. A 30-year-old with multilobar pneumonia, hypoxaemia (PaO₂ 55 mmHg), tachycardia (HR 130), and pH 7.30 scores approximately 100 points (Class IV) — but an 80-year-old male with the same presentation scores approximately 180 points (Class V). The physiological severity is identical, but the risk class differs dramatically.
Solution: In young patients (< 50) with significant physiological derangement, do not rely solely on the PSI class for disposition. If the patient meets ATS/IDSA criteria for severe CAP (mechanical ventilation, vasopressors, or ≥ 3 minor criteria), they need ICU-level care regardless of their PSI class. The CURB-65 or SMART-COP scores may be more appropriate for severity assessment in this age group.
The PSI estimates 30-day mortality risk — it does not directly assess whether a patient needs hospital-level care. A patient may have low mortality risk (Class II) but require admission for reasons the PSI does not capture: oxygen dependency, inability to tolerate oral medications (vomiting, dysphagia), decompensated diabetes, acute heart failure exacerbation, or lack of safe housing. Conversely, a high PSI class driven mainly by advanced age and chronic comorbidities may overstate the severity of the acute pneumonia episode.
Solution: Use the PSI to inform the mortality discussion, but make the admission decision based on the full clinical picture. Ask: “Can this patient safely manage at home for the next 48 hours?” If the answer is no for any reason — clinical, social, or logistical — admission is appropriate regardless of PSI class.
The two-step algorithm is intentionally designed so that low-risk patients (age ≤ 50, no comorbidities, normal vitals) are classified as Class I without needing laboratory testing. Skipping Step 1 and calculating the full point score for all patients defeats one of the PSI’s key benefits — reducing unnecessary blood draws and imaging in clearly low-risk patients.
Solution: Always start with Step 1. If the patient is ≤ 50 years old with no qualifying comorbidities and no vital sign abnormalities, classify as Class I and consider outpatient management without laboratory workup (unless clinically indicated for other reasons). This approach saves resources and accelerates the disposition decision for the majority of low-risk patients.
The PSI was not designed to determine which patients need intensive care — it was designed to identify which patients can go home. A patient may be Class III or even Class II yet still meet criteria for severe CAP requiring ICU admission (e.g., a young patient with bilateral pneumonia and septic shock). The ATS/IDSA severe pneumonia criteria, SMART-COP score, or the IDSA/ATS major criteria (mechanical ventilation, vasopressors) are more appropriate for ICU triage.
Solution: Use the PSI for the “safe to go home?” question and a separate assessment tool for the “needs ICU?” question. For patients in PSI Classes IV–V, apply the ATS/IDSA criteria to determine whether ICU-level monitoring and intervention are required, independent of the PSI class itself.
The PSI requires 20 variables including laboratory values and chest radiography — making it impractical for initial triage before test results are available. It does not incorporate social determinants of health, functional status, or the feasibility of outpatient care. In practice, it functions best as a decision-support tool calculated once laboratory and imaging results are available, rather than as a front-door triage instrument.
Quick Reference Summary
| Variable | Points | Variable | Points |
|---|---|---|---|
| Age (male) | = age | pH < 7.35 | +30 |
| Age (female) | = age − 10 | Neoplastic disease | +30 |
| Nursing home | +10 | Altered mental status | +20 |
| Liver disease | +20 | RR ≥ 30 | +20 |
| BUN ≥ 30 mg/dL | +20 | SBP < 90 | +20 |
| Na⁺ < 130 | +20 | Temp <35 / ≥40°C | +15 |
| CHF / CVD / Renal | +10 each | HR ≥ 125 | +10 |
| Glucose ≥ 250 | +10 | Hct < 30% | +10 |
| PaO₂ < 60 / SpO₂ < 90 | +10 | Pleural effusion | +10 |
The Golden Rule: The PSI is designed to answer one question: “Can this patient safely go home?” Classes I–II are strong candidates for outpatient management. Class III is the clinical decision point. Classes IV–V require inpatient care. But the PSI does not answer “Does this patient need ICU?” — use ATS/IDSA severe CAP criteria for that question.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
- 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. DOI: 10.1056/NEJM199701233360402
- Fine MJ, Stone RA, Singer DE, et al. Processes and outcomes of care for patients with community-acquired pneumonia. Arch Intern Med. 1999;159(9):970-980. DOI: 10.1001/archinte.159.9.970
- Aujesky D, Auble TE, Yealy DM, et al. Prospective comparison of three validated prediction rules for prognosis in community-acquired pneumonia. Am J Med. 2005;118(4):384-392. DOI: 10.1016/j.amjmed.2005.01.006
- Metlay JP, Waterer GW, Long AC, 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. DOI: 10.1164/rccm.201908-1581ST
- Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382. DOI: 10.1136/thorax.58.5.377
- Chalmers JD, Singanayagam A, Akram AR, et al. Severity assessment tools for predicting mortality in hospitalised patients with community-acquired pneumonia. Thorax. 2010;65(10):878-883. DOI: 10.1136/thx.2009.133280
- Dequin PF, Meziani F, Quenot JP, et al. Hydrocortisone in severe community-acquired pneumonia (CAPE COD). N Engl J Med. 2023;388(21):1931-1941. DOI: 10.1056/NEJMoa2215145
- Charles PG, Wolfe R, Whitby M, et al. SMART-COP: a tool for predicting the need for intensive respiratory or vasopressor support in community-acquired pneumonia. Clin Infect Dis. 2008;47(3):375-384. DOI: 10.1086/589754
- Yealy DM, Auble TE, Stone RA, et al. Effect of increasing the intensity of implementing pneumonia guidelines: a randomized, controlled trial. Ann Intern Med. 2005;143(12):881-894. DOI: 10.7326/0003-4819-143-12-200512200-00006
- Torres A, Cilloniz C, Niederman MS, et al. Pneumonia. Nat Rev Dis Primers. 2021;7(1):25. DOI: 10.1038/s41572-021-00259-0