Pneumonia severity index

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The pneumonia severity index (PSI) or PORT Score is a clinical prediction rule that medical practitioners can use to calculate the probability of morbidity and mortality among patients with community acquired pneumonia.[1]

The PSI/PORT score is often used to predict the need for hospitalization in people with pneumonia.[2] This is consistent with the conclusions stated in the original report that published the PSI/PORT score:[1] "The prediction rule we describe accurately identifies the patients with community-acquired pneumonia who are at low risk for death and other adverse outcomes. This prediction rule may help physicians make more rational decisions about hospitalization for patients with pneumonia."[1]

Mortality prediction is similar to that when using CURB-65.[3]


The rule uses demographics (whether someone is older, and is male or female), the coexistence of co-morbid illnesses, findings on physical examination and vital signs, and essential laboratory findings. This study demonstrated that patients could be stratified into five risk categories, Risk Classes I-V, and that these classes could be used to predict 30-day survival.


The purpose of the PSI is to classify the severity of a patient's pneumonia to determine the amount of resources to be allocated for care. Most commonly, the PSI scoring system has been used to decide whether patients with pneumonia can be treated as outpatients or as (hospitalized) inpatients.

  • A Risk Class I or Risk Class II pneumonia patient can be sent home on oral antibiotics.[4]
  • A Risk Class III patient, after evaluation of other factors including home environment and follow-up, may either:[5]
  • be sent home with oral antibiotics[4]
  • be admitted for a short hospital stay with antibiotics and monitoring.[4]
  • Patients with Risk Class IV-V pneumonia patient should be hospitalized for treatment.[4]


The PSI Algorithm is detailed below. An online, automated PSI calculator was once available on the US AHRQ website for Personal Digital Assistants that are no longer sold. In 2018 AHRQ presented a new toolkit on the basis of CURB-65, an older counterpart to the PSI. [6] In the 2019 ATS/IDSA Guidelines for the Diagnosis and Treatment of Adults with Community-acquired Pneumonia, PSI was recommended over CURB-65 because of lack of evidence supporting the safety and effectiveness of the latter. [7]

Step 1: Stratify to Risk Class I vs. Risk Classes II-V
Presence of:
Over 50 years of age Yes/No
Altered mental status Yes/No
Pulse ≥125/minute Yes/No
Respiratory rate >30/minute Yes/No
Systolic blood pressure <90 mm Hg Yes/No
Temperature <35 °C or ≥40 °C Yes/No
History of:
Neoplastic disease Yes/No
Congestive heart failure Yes/No
Cerebrovascular disease Yes/No
Renal disease Yes/No
Liver disease Yes/No
If any "Yes", then proceed to Step 2
If all "No" then assign to Risk Class I
Step 2: Stratify to Risk Class II vs III vs IV vs V
Demographics Points Assigned
If Male +Age (yr)
If Female +Age (yr) − 10
Nursing home resident +10
Neoplastic disease +30
Liver disease +20
Congestive heart failure +10
Cerebrovascular disease +10
Renal disease +10
Physical Exam Findings
Altered mental status +20
Pulse ≥125/minute +10
Respiratory rate >30/minute +20
Systolic blood pressure <90 mm Hg +20
Temperature <35 °C or ≥40 °C +15
Lab and Radiographic Findings
Arterial pH <7.35 +30
Blood urea nitrogen ≥30 mg/dl (9 mmol/liter) +20
Sodium <130 mmol/liter +20
Glucose ≥250 mg/dl (14 mmol/liter) +10
Hematocrit <30% +10
Partial pressure of arterial O2 <60mmHg +10
Pleural effusion +10
Σ <70 = Risk Class II
Σ 71-90 = Risk Class III
Σ 91-130 = Risk Class IV
Σ >130 = Risk Class V

Data source for derivation and validation

The rule was derived then validated with data from 38,000 patients from the MedisGroup Cohort Study for 1989, comprising 1 year of data from 257 hospitals across the US who used the MedisGroup patient outcome tracking software built and serviced by Mediqual Systems (Cardinal Health). One significant caveat to the data source was that patients who were discharged home or transferred from the MedisGroup hospitals could not be followed at the 30-day mark, and were therefore assumed to be "alive" at that time. Further validation was performed with the Pneumonia Patient Outcomes Research Team [PORT] (1991) cohort study. This categorization method has been replicated by others[8] and is comparable to the CURB-65 in predicting mortality.[8]

Derivation and validation data

Medisgroup Study (1989) PORT Validation Study (1991) Cohort
Derivation Cohort Validation Cohort Inpatients Outpatients All Patients
Risk Class no. of pts % died no. of pts % died no. of pts % died no. of pts % died no. of pts % died
I 1,372 0.4 3,034 0.1 185 0.5 587 0.0 772 0.1
II (<70) 2,412 0.7 5,778 0.6 233 0.9 244 0.4 477 0.6
III (71–90) 2,632 2.8 6,790 2.8 254 1.2 72 0.0 326 0.9
IV (91–130) 4,697 8.5 13,104 8.2 446 9.0 40 12.5 486 9.3
V (>130) 3,086 31.1 9,333 29.2 225 27.1 1 0.0 226 27.0
Total 14,199 10.2 38,039 10.6 1343 8.0 944 0.6 2287 5.2

Note: % Died refers to 30-day mortality.


  1. 1.0 1.1 1.2 Fine, MJ; Auble, TE; Yealy, DM; Hanusa, BH; Weissfeld, LA; Singer, DE; Coley, CM; Marrie, TJ; Kapoor, WN; et al. (Jan 1997). "A prediction rule to identify low-risk patients with community-acquired pneumonia". N Engl J Med. 336 (4): 243–250. doi:10.1056/NEJM199701233360402. PMID 8995086.
  2. Mark Williams; Scott A. Flanders; Winthrop F. Whitcomb (28 September 2007). Comprehensive hospital medicine: an evidence based approach. Elsevier Health Sciences. pp. 273–. ISBN 978-1-4160-0223-9. Retrieved 11 November 2010.
  3. Chalmers JD, Singanayagam A, Akram AR, et al. (October 2010). "Severity assessment tools for predicting mortality in hospitalised patients with community-acquired pneumonia. Systematic review and meta-analysis". Thorax. 65 (10): 878–83. doi:10.1136/thx.2009.133280. PMID 20729231.
  4. 4.0 4.1 4.2 4.3 Scott Kahan (1 January 2003). In a Page Medicine. Lippincott Williams & Wilkins. ISBN 978-1-4051-0325-1. Page 40
  5. "NewYork-Presbyterian Hospital Guidelines for the Empiric Management of Adult Patients with Community-Acquired Pneumonia (CAP) and IV to PO Conversion" (PDF). May 6, 2010. Archived from the original (PDF) on 2016-03-08. Retrieved 2015-05-22.
  6. Agency for Healthcare Research and Quality, Rockville, MD. (2018). "Community-Acquired Pneumonia Clinical Decision Support Implementation Toolkit. Content last reviewed January 2018". Archived from the original on 2019-07-02. Retrieved 2023-01-29.{{cite web}}: CS1 maint: multiple names: authors list (link)
  7. American Thoracic Society and Infectious Diseases Society of America (2019). "Diagnosis and Treatment of Adults with Community-acquired Pneumonia: An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America". American Journal of Respiratory and Critical Care Medicine. 200 (7): e45–e67. doi:10.1164/rccm.201908-1581ST. PMC 6812437. PMID 31573350.
  8. 8.0 8.1 Aujesky D, Auble TE, Yealy DM, et al. (2005). "Prospective comparison of three validated prediction rules for prognosis in community-acquired pneumonia". Am. J. Med. 118 (4): 384–92. doi:10.1016/j.amjmed.2005.01.006. PMID 15808136.

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