Procalcitonin-guided therapy for pneumonia resulted in better antibiotic stewardship with fewer deaths, antibiotic associated side effects and no worse outcomes in a 2017 Cochrane review of 24 trials involving 6,708 patients in a variety of settings. One of the criticisms of procalcitonin is that it has poor specificity, so it will have many false positives for identifying bacterial infections. It’s also an expensive test. Recently, a group of Swiss researchers evaluated the use of procalcitonin, alone or with point of care ultrasound (POCUS) of the lung, for reducing inappropriate antibiotic prescriptions in a pragmatic trial.

The trial was conducted between September 2018 and March 2020, ending prematurely because of the COVID-19 pandemic. In this cluster-randomized trial, 60 general practitioners were randomized to treat adult patients with a presentation concerning for pneumonia to either usual care, antibiotic treatment based on point-of-care procalcitonin levels, or treatment based on a combination of a positive procalcitonin level and a POCUS-identified infiltrate. The primary outcome of this trial was the percent of patients prescribed an antibiotic by day 28 after presentation.

On day one, 57 percent of those in the usual care group received antibiotics, compared to 18 percent of those in the procalcitonin alone and 16 percent of those in the procalcitonin plus POCUS group. By day seven, 61 percent of those in the usual care group had received antibiotics compared to 30 percent in the other groups. By day 28, the difference was 70 percent in the usual care group with 40 percent in the procalcitonin and 41 percent in the procalcitonin plus POCUS group. There were no differences in clinical failure of care or adverse outcomes between the three groups. Of note, 55 percent of the patients in the usual care group received chest radiographs compared to about 20 percent in the group managed by either procalcitonin alone or procalcitonin plus POCUS. POCUS was performed in six percent of the patients in that group, of whom 67 percent had a POCUS identified infiltrate. The odds ratio of getting antibiotics in this study if procalcitonin was used to guide care was 0.29 (95% CI 0.13 to 0.65). Results were significant with both intention-to-treat and per-protocol analyses.

This study suggests that adding a procalcitonin test to usual care will reduce the likelihood of overprescribing antibiotics by about 66 percent, given that there were no differences in clinical outcomes between groups but reduced antibiotic prescribing in the procalcitonin group. POCUS testing didn’t add anything to procalcitonin, although of course the number of ultrasounds was small, and POCUS wasn’t allowed to fly solo in this study. One outcome not measured is cost to the healthcare system of adding an expensive blood test. On the other hand, there were fewer chest x-rays in the group that was tested for procalcitonin so that is an offsetting factor. We also don’t know the balance of fiscal cost vs. the cost of antibiotic resistance to the worldwide community. Short of convincing practitioners to “just say no” and trust their clinical diagnostic skills, procalcitonin seems to reduce unnecessary antibiotic prescribing.

For more information, see the topic Procalcitonin-guided Antibiotic Therapy in DynaMed®.