Comparison of direct microscopy, culture and calcofluor white for the diagnosis of onychomycosis

Abstract

Background: Mycological diagnosis of onychomycosis can be performed by direct microcopy (KOH), cultures and calcofluor white.

Aims: To compare the percentage of positivity and the degree of correlation of KOH, cultures and calcofluor white for the diagnosis of onychomycosis.

Methods: Descriptive, transversal and comparative study. Samples of toenails with onychomycosis were used for KOH, cultures and calcofluor white under fluorescence. The percentage of positivity of the different techniques was calculated and the degree of correlation between them was determined (Epi Info v 3.4.3(©)).

Results: KOH was positive in 66.67% of the cases, cultures in 33.33% and calcofluor white in 57.58%. KOH and calcofluor white had a higher percentage of positivity than culture (p<0.01 and p<0.05 respectively). The degree of correlation between KOH and calcofluor white was excellent (κ=0.8085; p<0.0001); however, the degree of correlation between KOH and culture and between calcofluor white and culture was poor.

Conclusions: The use of calcofluor white is not recommended in routine laboratories because it does not seem to bring any additional benefits when comparing with KOH. This is especially important when funding is a great problem.