Clinical Progress Note: Procalcitonin in the Diagnosis and Management of Community-Acquired Pneumonia in Hospitalized Adults

There is insufficient evidence to support the use of serum procalcitonin to withhold initial antibiotics in patients with a clinical syndrome consistent with bacterial CAP. However, the literature supports the use of procalcitonin for the early discontinuation of antibiotics for cases in which the probability of bacterial CAP is low, and procalcitonin remains below 0.1 ng/mL (Figure).

Serial measurements of procalcitonin every one to two days may also be used when clinical uncertainty remains regarding the need for antibiotics. Very low or significantly decreasing procalcitonin levels in patients with CAP and no identified bacterial pathogen likely indicate the infection was not bacterial or was bacterial, but has now been adequately treated with antibiotics. For cases of proven bacterial etiology or high clinical suspicion of bacterial CAP, there is insufficient evidence to recommend the early discontinuation of antibiotics based on procalcitonin levels short of the recommended five-day course according to current guidelines.¹⁰ Future clinical trials are needed to determine if procalcitonin guidance can safely decrease the duration of antibiotic therapy for confirmed bacterial CAP to less than five days.

There are discrepancies between the apparent test characteristics of procalcitonin and the recommended antibiotic decisions in many procalcitonin algorithms. For example, algorithms discourage antibiotics when procalcitonin values are 0.1-0.24 ng/mL, and encourage (or even strongly encourage) antibiotic use for higher procalcitonin values of 0.25-1.0 ng/mL. However, the LRs for these ranges are identical and are approximately 1.0 (Table), suggesting that decision-making should be similar across the entire procalcitonin range of 0.1 to 1.0. Future clinical trials should study revised algorithms with different cut-points, including the thresholds found in our secondary analysis of multilevel LRs. Until then, we believe there is insufficient evidence to deviate from current antibiotic decision recommendations at the traditional cut-points.

While procalcitonin is an imperfect biomarker for discriminating bacterial and nonbacterial etiologies of CAP, it may still provide helpful information for the hospitalist in antibiotic decision-making in the same way we apply other commonly used clinical variables such as fever, white blood cell count, band count, and the pattern of infiltrate in chest imaging.

Procalcitonin should be interpreted cautiously in certain populations in which it has not been extensively studied (eg, immunocompromised) or in noninfectious conditions that may elevate procalcitonin, such as major physiologic stress (eg, surgery, trauma, burns) and end-stage renal disease.^12-14 Further investigation is needed to determine the efficacy and safety of procalcitonin-guided antibiotic therapy in these populations.

• Based on currently available data, a low procalcitonin value should not be used as a stand-alone test to withhold antibiotics in a patient with CAP.
• Serum procalcitonin measurements may help guide the early discontinuation of antibiotics for patients who the treating clinician judges the risks of bacterial etiology and clinical deterioration to be low.
• Interpret procalcitonin cautiously in immunocompromised patients, undergoing severe physiologic stress, or have underlying end-stage renal disease.
• Serum procalcitonin serves as an adjunct to, rather than a substitute for, clinical judgment.