Multicenter evaluation of a commercial PCR-enzyme-linked immunosorbent assay diagnostic kit (Onychodiag) for diagnosis of dermatophytic onychomycosis

Abstract

We prospectively evaluated a new PCR-enzyme-linked immunosorbent assay kit (Onychodiag; BioAdvance, France) for the diagnosis of dermatophytic onychomycosis by testing nail samples from 438 patients with suspected onychomycosis and from 108 healthy controls in three independent laboratories. In two laboratories, samples were collected by trained mycologists as close as possible to the lesions (proximal samples). In one laboratory, samples were collected by other physicians. All samples were processed by conventional mycological techniques and by Onychodiag, blindly to the mycological results. An additional distal sample, collected by clipping the nail plate, was obtained from 75 patients and tested with Onychodiag alone. In patients with culture-proven dermatophytic onychomycosis, the sensitivity of Onychodiag was 83.6% (87.9% including the gray zone) and ranged from 75 to 100% according to the laboratory and the sampling conditions. The specificity was 100% when healthy subjects were considered true negative controls. Onychodiag was positive on 68 patient samples that were sterile or yielded nondermatophyte species in culture. Based on the results of Onychodiag for mycologically proven positive samples and true-negative samples, these results were considered true positives, and the poor performance of mycology on these samples was attributed to inconvenient sampling conditions or to contaminants. When tested on distal samples, Onychodiag was positive in 49/53 (92%) cases of proven dermatophytic onychomycosis. Finally, with either proximal or distal samples, Onychodiag provided a diagnosis of dermatophytic onychomycosis within 24 to 48 h after sampling, and its sensitivity was close to that of mycological techniques applied to proximal samples.

FIG. 1.

Study design and participating laboratories assessing Onychodiag on healthy control samples (study 1), RPS (study 2), and DS compared to RPS (study 3) and Reg S (study 4).