Objective: To determine the value of repeated Clostridium difficile cytotoxicity assays (CA).
Design: All CAs performed during 1993 were retrospectively reviewed and correlated with clinical data. Assays were grouped into episodes, which were defined as one or more successive tests performed on a single patient within 7 days or less of each other.
Setting: A 751-bed tertiary care facility.
Patients: All patients with Clostridium difficile CAs submitted to the microbiology laboratory.
Results: There were 947 episodes with two or more CAs. In 15 of these episodes, a negative CA result was followed by a positive result, and in 25 cases, a positive result was followed by a negative one. We reviewed the clinical data for these cases. Of the 947 episodes with two or more CAs, the repeated assays provided new information that was used in patient care in fewer than nine cases. Repeated testing within 7 days of an initial CA accounted for 36% of all assays performed, but provided clinically useful information in only about 1% of cases.
Conclusions: Clostridium difficile CAs should not be repeated within a 7-day period.