June 2, 2021
By Zeina A. Kanafani, MD, MS, FIDSA
Published data support the use of procalcitonin to distinguish between bacterial and viral infections of the lower respiratory tract and to aid in the diagnosis of sepsis in critically ill patients. On the other hand, elevated procalcitonin levels have been observed in patients with severe COVID-19, and procalcitonin has been suggested as a marker for clinical deterioration in such patients. The purpose of a recent analysis in Antimicrobial Agents and Chemotherapy was to determine whether procalcitonin can distinguish between bacterial coinfection and the inflammatory response caused by COVID-19.
This was a retrospective cohort study that included 2,443 adults presenting to the emergency department with COVID-19. All patients underwent measurement of procalcitonin levels upon admission and every 72 hours thereafter. The investigators then identified cases of concomitant community-associated bacteriuria (88), bacteremia (47), and bacterial pneumonia (24) in a total of 148 patients, giving a prevalence of community-associated bacterial infection (CAI) of 6.1%.
Patients with any CAI had higher mean procalcitonin levels compared to those without CAI (13.16 ng/ml vs. 2.00 ng/ml; P = .0091). Elevated procalcitonin levels were most prominent with bacteremia episodes (mean 34.25 ng/ml), followed by bacteria pneumonia (16.42 ng/ml) and bacteriuria (5.15 ng/ml). At a procalcitonin cutoff of 0.25 ng/ml, the test characteristics for the various infections were: sensitivity 57%, 68%, and 71%; specificity 53%, 53%, and 53%; positive predictive value 43%, 27%, and 15%; and negative predictive value 97%, 99%, and 99% for detection of community-associated bacteriuria, bacteremia, and bacterial pneumonia, respectively.
An elevated procalcitonin level therefore seems to be a poor predictor of CAI among patients with COVID-19, and systemic inflammation caused by the viral infection appears to cause a rise in procalcitonin levels. However, given the high negative predictive value across all types of infection, a normal procalcitonin level will effectively rule out a bacterial coinfection in this patient population.