The findings of this study demonstrate that availability and use of an in-house, rapidly resulting PCT assay did not reduce antimicrobial therapy durations. Baseline antimicrobial durations of therapy are short at the study institution, concordant with national guideline recommendations, due to the presence of a progressive antimicrobial stewardship program that provides recommendations on antimicrobial use for the entirety of the hospital. In contrast, many studies which have analyzed PCT utilization and reported reductions in antimicrobial therapy days, reported baseline treatment durations longer than minimum recommended guideline durations. For example, a 2018 meta-analysis that analyzed PCT guided use of antibiotics compared to clinical judgment for acute respiratory infections found a difference in antibiotic exposure of 5.7 days vs 8.1 days (95% CI, -2.71, 2.15, p < 0.0001) in the PCT-guided group compared to the clinical judgment group alone . Results of this study are consistent with the results of another 2018 meta-analysis that compared PCT guided use of antibiotics compared to clinical judgment for a variety of infectious etiologies . The results of the meta-analysis found no difference in mean days of treatment with 4.3 vs 4.3 days (95% CI, -0.6 to 0.5, p = 0.87) in the PCT-guided and clinical judgment alone guided groups, respectively. This study also found no significant difference in antibiotic days by day 30 in any pre-specified subgroup analysis.
Given the lack of difference in antimicrobial therapy durations observed between groups, it is evident that receipt of the laboratory value within a matter of hours does not result in a difference in use of this lab for antimicrobial decision-making in a manner that improves rates of de-escalation or discontinuation. This assessment is further validated by the scarcity with which PCT was mentioned in the patient chart as a tool utilized in clinical decision making. This conclusion does not account for non-documented clinical decision making, which cannot be studied via retrospective chart review.
In addition to lack of utility regarding rapid-result PCT labs at reducing antimicrobial durations, many of the patients who had a PCT laboratory value ordered in both the send-out and rapid-result group had a comorbidity that could lead to a noninfectious elevation of or falsely low level of PCT, 34.9% and 46.8% respectively. Because interpretation of PCT in these patients is not standardized at this institution, the lab value likely does not provide high utility in guiding antimicrobial de-escalation or discontinuation.
The study population also differed significantly between the send-out and rapid-result groups, with more critically ill patients present in the rapid-result cohort. This difference is attributed to increased provider lab orders influenced by ease of obtaining quick results with an in-house assay. By analyzing the differences between subgroups of critically ill and non-critically ill patients, investigators attempted to mitigate confounding influence of prolonged antimicrobial durations in critically ill patients compared to non-critically ill patients. An additional consideration that would provide useful knowledge towards the utility of PCT would be to collect information regarding PCT values guiding duration of antibiotics on discharge as this endpoint was not assessed in this study.
While this study is limited by its retrospective nature at a single health system, it does highlight several points. First, we observed a lack of effect on reduction in durations of antimicrobial use where a robust antimicrobial stewardship program is already in place to closely monitor this. It also highlights a large percentage of inappropriately ordered PCT assays in patients with exclusions to accurate interpretation.
Cost per test was reduced by bringing PCT testing in-house, however, a substantial increase was observed in the volume of PCT test orders by providers. This resulted in increased hospital costs without an associated reduction in days of antimicrobial therapy. Thus, the availability of in-house PCT testing did not result in financial benefit to the study institution or clinical benefit in reduced days of antimicrobial therapy. Based on the result of this study, our institution has elected to remove PCT from the adult laboratory formulary.