A Comparative Study for Evaluating the Diagnostic Capacity of the Dermatophyte Test Strip for Tinea Unguium

Background: Both direct microscopic examination and fungal culture are standard diagnostic methods for tinea unguium diagnosis. However, the accuracy of these tests is low and the results tend to be dependent on the skills of the performer. The Dermatophyte Test Strip, a newly developed diagnostic tool that is used to detect dermatophytes, facilitates the diagnosis of tinea unguium using immunochromatography. Objective: We compared the diagnostic capacity of the Dermatophyte Test Strip and conventional diagnostic methods for the detection of dermatophytes in clinically suspected tinea unguium specimens in Korea. Methods: Direct microscopic examination and the Dermatophyte Test Strip were performed on all specimens. If the results differed between the two methods, we used polymerase chain reaction (PCR) analysis to confirm the dermatophyte presence. Results: Of the 120 specimens, 77 (64.2%) showed positive results on the Dermatophyte Test Strip and 66 (55.0%) on the direct microscopic examination. PCR analysis was performed on the 27 specimens whose results differed between the two tests, and all these specimens showed positive results on PCR analysis. When comparing the results of direct microscopy adjusted with PCR with those of the Dermatophyte Test Strip, the positive/negative/overall concordance rates were 100%, 81.4%, and 93.3%, respectively, while the kappa coefficient was 0.85 (95% confidence interval, 0.75∼0.95). Conclusion: This study suggests that the Dermatophyte Test Strip, a practical diagnostic kit that detects dermatophytes without using other technical instruments, may be a valuable diagnostic tool for tinea unguium and may reduce the unnecessary use of antifungal agents. (Korean J Dermatol 2020;58(7):459∼464)