Pneumonia Severity Index (PSI)

Pneumonia Severity Index

There are two steps of evaluation in the pneumonia severity score, the first that lists criteria and asks for personal history of certain diseases and a second one with more diverse questions.

All of this is aimed to make community acquired pneumonia diagnosis faster and to provide information about individual patient mortality risk.

Step 1 consists of two items:

The first item checks for the presence of the following:

■ Over 50 years of age;

■ Altered mental status;

■ Pulse ≥125/minute;

■ Respiratory rate >30/minute;

■ Systolic blood pressure;

■ Temperature <35°C or ≥40°.

The second item checks for personal history of any of the following:

■ Neoplastic disease;

■ Congestive heart failure;

■ Cerebrovascular disease;

■ Renal disease;

■ Liver disease.

Step 2 is more specific and is aimed at distinguishing between risk classes II to V.

The first three questions have to do with patient demographics:

■ Gender: Because the PSI accounts for gender related risk factors.

■ Age: number of years is directly transformed in points for men whilst for women, 10 is subtracted before the age can be used in the score.

■ Nursing home resident status: if positive, adds 10 points to the final score.

The other three questions have specific answer choices, as detailed below, along with the number of points they are awarded.

Comorbidity:

■ 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;

■ Temperature <35°C or ≥40°C (+15).

Lab and Radiographic findings:

■ Arterial pH;

■ Blood urea nitrogen ≥30 mg/dl (11 mmol/liter) (+20);

■ Sodium;

■ Glucose ≥250 mg/dl (14 mmol/liter) (+10);

■ Hematocrit <30% (+10);

■ Partial pressure of arterial O2;

■ Pleural effusion (+10).

PSI score interpretation

The first step of the PSI distinguishes between patients under risk class I and patients under risk classes II to V.

The patient belongs to the first class in case none of the items in step one is positive and thus the evaluation can stop.

In case any of the items is positive, the evaluation continues with step 2 which discriminates between risk classes II, III, IV and V.

Each of the items belonging to step 2 is awarded a number of points (from 10 to 30), depending on their gravity and likelihood of impact on pulmonary function.

The association between PSI score and risk classes is:

■ ≤70: Risk Class II;

■ 71 - 90: Risk Class III;

■ 91 - 130: Risk Class IV;

■ >130: Risk Class V.

This table is more specific and details the severity of risk and treatment recommendations:

About the study

The original study, conducted by Dr Fine in 1997, collected data from 14,199 patients with community-acquired pneumonia. The prediction rule stratified them in the five classes discussed above.

A subsequent validation study has taken place in 1991 on 38,039 inpatients and on 2,287 inpatients and outpatients in the Pneumonia Patient Outcomes Research Team (PORT) cohort study.

A comparison of PSI with CURB-65, another pulmonary stratification tool, indicated that the former shows less specificity (52.2% compared to 74.6%) in terms of risk prediction, although both scores carry a similar sensitivity, and more so, in ICU, the PSI fares slightly better.

Original study

Fine MJ, Auble TE, Yealy DM, Hanusa BH, Weissfeld LA, Singer DE, Coley CM, Marrie TJ, Kapoor WN. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997; 336(4):243-50.

Other references

1. Aujesky D, Auble TE, Yealy DM, Stone RA, Obrosky DS, Meehan TP, Graff LG, Fine JM, Fine MJ. Prospective comparison of three validated prediction rules for prognosis in community-acquired pneumonia. Am J Med. 2005; 118(4):384-92.

2. Lim WS, van der Eerden MM, Laing R, Boersma WG, Karalus N, Town GI, Lewis SA, Macfarlane JT. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003; 58(5):377-82.