What is a high PSI score?

PSI Class IV (score 91–130) and Class V (score >130) indicate high-risk pneumonia with 30-day mortality rates of 8.2% and 29.2% respectively. Class IV/V patients require hospital admission, with Class V typically requiring ICU or high-dependency care. PSI Classes I–III (score ≤90) are low-risk and can generally be managed as outpatients.

PSI vs CURB-65 — which is better?

Both are validated clinical tools. PSI (PORT score) evaluates 20 variables and is superior for identifying low-risk patients who can safely receive outpatient treatment, safely reducing hospital admissions. CURB-65 uses 5 variables and is faster at the bedside in busy emergency rooms. IDSA/ATS 2019 guidelines endorse either instrument.

What are the criteria for PSI Class I?

PSI Class I applies to patients aged ≤50 years with no nursing home residency, none of the 5 co-morbidities (neoplasm, liver disease, CHF, CVD, renal disease), and normal physical examination vitals (normal mental status, pulse <125, RR <30, SBP ≥90, temp 35–39.9°C). Class I patients have a 30-day mortality of 0.1% and do not require routine blood draws or inpatient admission.

What antibiotics are recommended for community-acquired pneumonia based on PSI?

Per ATS/IDSA 2019 guidelines: Outpatients without comorbidities (Class I–II) receive high-dose amoxicillin or doxycycline. Outpatients with comorbidities (Class II–III) receive combination amoxicillin-clavulanate + azithromycin, or respiratory fluoroquinolone monotherapy. Inpatients (Class IV–V) receive IV beta-lactam (ceftriaxone or ampicillin-sulbactam) + azithromycin, or respiratory fluoroquinolone.

PSI / PORT Score Calculator | Pneumonia Severity Index

Q: What antibiotics are recommended for community-acquired pneumonia based on PSI?

Per ATS/IDSA 2019 guidelines: Outpatients without comorbidities (Class I–II) receive high-dose amoxicillin or doxycycline. Outpatients with comorbidities (Class II–III) receive combination amoxicillin-clavulanate + azithromycin, or respiratory fluoroquinolone monotherapy. Inpatients (Class IV–V) receive IV beta-lactam (ceftriaxone or ampicillin-sulbactam) + azithromycin, or respiratory fluoroquinolone.

Pneumonia Severity Index (PSI / PORT) Calculator

Calculate the Pneumonia Severity Index (PORT Score) for community-acquired pneumonia (CAP). Predict 30-day mortality, stratify Risk Classes I–V, determine outpatient vs. inpatient admission, and select empiric antibiotics per ATS/IDSA 2019 guidelines.

Fine et al. (NEJM 1997)ATS / IDSA 2019 AlignedRisk Classes I–V

1PSI Risk Classes, Mortality & Admission Setting

Risk Class	PORT Score Range	30-Day Mortality	Recommended Triage Setting
Class I	Age ≤50 + No Comorbidities + Normal Exam	0.1%	Outpatient
Class II	≤ 70 points	0.6%	Outpatient
Class III	71–90 points	2.8%	Outpatient or Short Stay Observation
Class IV	91–130 points	8.2%	Inpatient Medical Ward
Class V	> 130 points	29.2%	Inpatient / Immediate ICU Triage

2Empiric Antibiotic Selection (ATS / IDSA 2019)

Outpatient (Class I–II) — Previously Healthy, No Risk Factors

First-Line: Amoxicillin 1 g PO TID × 5 days.
Alternative / Atypical coverage: Doxycycline 100 mg PO BID × 5 days.
Macrolides (Azithromycin 500 mg Day 1, then 250 mg daily) only in regions with pneumococcal macrolide resistance <25%.

Outpatient with Comorbidities (Class II–III)

Combination Therapy: Amoxicillin-clavulanate (875/125 mg PO BID or 2000/125 mg PO BID) plus Azithromycin 500 mg Day 1 then 250 mg daily, OR Doxycycline 100 mg BID.
Monotherapy: Respiratory fluoroquinolone (Levofloxacin 750 mg PO daily or Moxifloxacin 400 mg PO daily) × 5 days.

Inpatient Non-ICU (Class IV) & Severe Inpatient (Class V)

Non-ICU Inpatient: IV Beta-lactam (Ceftriaxone 1–2 g IV daily or Ampicillin-sulbactam 1.5–3 g IV q6h) plus IV/PO Azithromycin 500 mg daily, OR Respiratory fluoroquinolone monotherapy.
Severe CAP / ICU (Class V): IV Beta-lactam (Ceftriaxone or Cefotaxime) plus IV Azithromycin or IV Levofloxacin.
Add MRSA coverage (Vancomycin or Linezolid) and antipseudomonal coverage (Piperacillin-tazobactam, Cefepime, or Meropenem) if prior isolation or specific hospital validation exists.

3PSI / PORT vs. CURB-65 Comparison

Clinical Attribute	Pneumonia Severity Index (PSI)	CURB-65 Score
Total Criteria Evaluated	20 variables across 4 tiers	5 variables
Primary Strength	Superior for identifying low-risk patients safe for outpatient therapy; reduces unnecessary hospitalizations.	Rapid bedside triage; excellent for identifying patients who will deteriorate.
Laboratory Requirements	Requires ABG, electrolytes, BUN, glucose, hematocrit, and CXR.	Requires only Serum Urea / BUN.
Guideline Endorsement	Preferred by ATS / IDSA 2019	Preferred by British Thoracic Society (BTS)

4Clinical Utility & Two-Step Triage

The Pneumonia Severity Index was developed from the Pneumonia Patient Outcomes Research Team (PORT) cohort of over 14,000 inpatients and validated in >38,000 individuals across North America. The model employs a validated two-step decision rule:

Step 1 (Risk Class I Assessment): Identifies patients aged ≤50 years who have zero comorbid illnesses (cancer, liver failure, heart failure, stroke, renal disease) and completely normal vital signs. These patients have a 30-day mortality of 0.1% and do not require laboratory blood sampling or chest radiography for severity calculation.

5Frequently Asked Questions

Clinical Takeaway: The PSI score safely decreases hospital admissions by objective identification of low-risk Class I–II patients. Always integrate clinical judgment: patients with intractable vomiting, cognitive impairment living alone, or hypoxemia warrant admission regardless of a low composite score.

Medical Disclaimer: This clinical calculator is designed for qualified healthcare professionals. It does not replace clinical judgment. Social factors, oxygen requirements, oral medication tolerance, and local pathogen resistance patterns must be synthesized into final admission decisions.