Effective utilization of C. difficile PCR and identification of clinicopathologic factors associated with conversion to a positive result in symptomatic patients.

OBJECTIVES: We assess the diagnostic yield of repeat testing for C. difficile using molecular methods within 7days of a negative test and identify specific factors associated with conversion from negative to positive test result within a 7-day period to aid in selective test utilization.

METHODS: A retrospective chart review of 20,866 laboratory test orders for C. difficile PCR was conducted. The test result, clinicopathologic patient features, and previous test results were recorded. Univariate and multivariate analysis was conducted to compare patients with initial and repeat negative results (n=248) to a group of patients with conversion from negative to positive results within 7days.

RESULTS: Univariate analysis demonstrated a history of C. difficile infection, receipt of antibiotics within 14days, and duration of hospital stay as factors significantly different between patients with repeat negative and conversion to positive C. difficile test result. Only history of C. difficile infection was significantly different upon multivariate analysis.

CONCLUSIONS: Identification of prior C. difficile infection as the only factor significantly correlated with conversion from negative to positive C. difficile test result within 7days aids in selective test utilization and reduces the costs associated with unnecessary laboratory testing.