Schuetz et al developed algorithms for guiding antibiotic therapy in various situations using the serum procalcitonin concentration. The authors are from Harvard School of Public Health, Massachusetts General Hospital and McMaster University.

Patient selection: moderate risk (moderate acuity) pneumonia



(1) serum procalcitonin concentration in µg/L on admission

(2) serum procalcitonin concentration in µg/L every 2-3 days

(3) clinical status


Antibiotics are started on admission if one or both of the following are present:

(1) serum procalcitonin >= 0.25 µg/L (especially if >= 0.5 µg/L)

(2) the patient is clinically unstable

(3) the patient is at high risk for an adverse outcome

(4) there is evidence of a bacterial pathogen (from Gram-stain, etc)


Antibiotic therapy is strongly discouraged if both of the following are present:

(1) the serum procalcitonin is < 0.1 µg/L

(2) the patient is stable and at low risk for an adverse outcome


Initial Management

Followup Decisions

antibiotics started

continue or change regimen if the procalcitonin level does not decline or if the patient does not improve clinically

antibiotics started

consider discontinuing antibiotics if serum procalcitonin decreases < 0.1 µg/L and the patient improves

antibiotics not started

start antibiotics if serum procalcitonin >= 0.25 µg/L or patient deteriorates

antibiotics not started

consider discharge if serum procalcitonin continues to be low and the patient is improving


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