Elevated procalcitonin levels indicate an infection is more likely to be bacterial than viral in etiology. Several trials have shown that antibiotic usage can be reduced through the use of serum procalcitonin levels to guide management decisions, and the recently published ProHOSP trial is the largest such study to date (level 1 [likely reliable] evidence). Procalcitonin-based guidelines were compared to standard guidelines for antibiotic treatment in 1,381 emergency department patients with severe lower respiratory infections. Treatment recommendations based on procalcitonin levels were: antibiotics strongly discouraged if procalcitonin < 0.1 mcg/L, antibiotics discouraged if procalcitonin 0.1-0.25 mcg/L, antibiotics recommended if procalcitonin 0.25-0.5 mcg/L, antibiotics strongly recommended if procalcitonin > 0.5 mcg/L. Follow-up levels were drawn to monitor status and guide changes in treatment.

Procalcitonin-based treatment was associated with shorter mean duration of antibiotic exposure (5.7days vs. 8.7 days, p < 0.05) and with reduced rates of antibiotic prescriptions in all patients regardless of diagnosis (75% vs. 87.7%, NNT 9, 95% CI 7-13) and in subgroups of patients with COPD exacerbation (48.7% vs. 69.9%, NNT 5) or acute bronchitis (23.2% vs. 50%, NNT 4).  Patients in the procalcitonin group had significantly lower rates of recurrence or rehospitalization (3.7% vs. 6.5%, NNT 36) and antibiotic-related adverse events (19.8% vs. 28.1%, NNT 12).  There were no significant differences in mortality (5.1% vs. 4.8%), intensive care admission (6.4% vs. 8.7%) or overall rate of adverse outcomes (15.4% vs. 18.9%) (JAMA 2009 Sep 9;302(10):1059).

For more information, see the Procalcitonin levels in patients with respiratory infections topic in DynaMed.