An in-office diagnostic procedure to detect dermatophytes in a nationwide study of onychomycosis patients.

PURPOSE To evaluate in-office dermatophyte test medium (DTM) culture as an alternative to traditional laboratory fungal culture for confirming a diagnosis of onychomycosis, and to determine the prevalence of dermatophytes as a cause of onychomycosis in patients not participating in a clinical trial. DESIGN This nationwide multicenter prospective study enrolled 1100 adult patients with suspect onychomycosis. DTM and laboratory fungal culture results were compared for individual patients. METHODOLOGY The 310 participating physicians obtained patient nail-bed specimens and divided them for testing by both diagnostic methods. The paired results of the two culture methods were compared using the kappa statistic. PRINCIPAL FINDINGS Paired culture results were available for 975 of the 1100 enrolled patients. DTM results agreed with central laboratory cultures in 70 percent of cases. The kappa value of 0.40 indicated a moderate degree of correspondence between the two testing modalities. Overall, DTM culture indicated a dermatophyte in 616 patient specimens (56 percent) and central laboratory culture identified a dermatophyte in 528 of the specimens (48 percent). For the entire study population, dermatophytes were identified in 93 percent of the positive central laboratory cultures, confirming that dermatophytes caused the vast majority of the infections. The cost of each DTM culture was approximately $1, compared to $25 for each laboratory fungal culture. CONCLUSION This study demonstrates that the in-office DTM culture for diagnosing onychomycosis has comparable utility to the traditional laboratory fungal culture, is less expensive, and yields faster results.