Tinea unguium is a common nail disease caused by dermatophytes. Although direct potassium hydroxide (KOH) microscopy and fungal culture are considered the gold standard for diagnosing this disease, their accuracy is insufficient. A lateral flow immunochromatographic assay (LFIA) kit, using a monoclonal antibody against Trichophyton rubrum, was developed and its sensitivity was recently improved 50% in vitro relative to its earlier version. The present study aimed to validate the clinical utility of this improved LFIA kit for diagnosing tinea unguium in comparison with direct KOH microscopy. A similar trial was simultaneously performed using scale samples from patients with tinea pedis to determine the assay's diagnostic potential. Nail samples, approximately 2 mg in weight, were collected from 112 non-treated tinea unguium patients and 56 non-tinea unguium patients. Samples from 25 tinea pedis patients and 20 non-tinea pedis patients were also collected. The sensitivity and specificity of the LFIA kit for tinea unguium was 84.8% (95/112) (95% confidence interval [CI], 76.8-90.9) and 83.9% (47/56) (95% CI, 71.7-92.4), respectively. The inconsistency rate was 15.5% (26/168) (95% CI, 10.4-21.9). The sensitivity and specificity of the LFIA kit for tinea pedis was 84.0% (21/25) and 100.0% (20/20), respectively. These results suggest that for diagnosing tinea unguium, the LFIA kit is a useful supplement to, but not a replacement for, direct KOH microscopy. For definitive diagnosis of suspected cases, appropriate sampling, repeated examinations, and a combination of diagnostic techniques are essential.
Keywords: Trichophyton rubrum; direct microscopy; onychomycosis; test strip; tinea pedis.
© 2021 Japanese Dermatological Association.