How is the severity of community-acquired pneumonia (CAP) estimated?

Updated: Oct 31, 2019
  • Author: Stephanie L Baer, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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The Pneumonia Severity Index (PSI) is preferred over the CURB-65 (confusion, uremia, respiratory rate, low blood pressure, age >65 years) for determining outpatient verses inpatient treatment. Patients with PSI class IV-V may need hospitalization or more intensive in-home services. Severe pneumonia is defined as having 1 major criteria (ie, septic shock requiring vasopressors or respiratory failure requiring mechanical ventilation) or 3 minor criteria, as follows:

  • Respiratory rate of 30 or more breaths per minute
  • PaO 2/FIO 2 ratio of 250 or less
  • Multilobar infiltrates
  • Confusion
  • Uremia
  • Leukopenia (WBC < 4000 cells/µl)
  • Thrombocytopenia (platelet count < 100,000/µl)
  • Hypothermia
  • Hypotension

These are the primary criteria to use to determine if a patient requires ICU admission. CURB-65 was designed to predict mortality risk; CRB-65 is similar but is used when certain laboratory tests are unavailable. Some scoring systems (eg, CURXO and SMART-COP) focus on the severity of CAP and likelihood of requiring ventilatory or circulatory support, whereas others (eg, PSI score) help determine whether CAP requires hospitalization.

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