Comparative study of efficacy, rapidity of detection, and cost-effectiveness of potassium hydroxide, calcofluor white, and Chicago sky blue stains in the diagnosis of dermatophytoses.

Background: The diagnosis of superficial mycosis such as dermatophytosis is often done clinically. However, in difficult cases, a rapid test with high sensitivity and specificity helps in the immediate confirmation and administration of treatment.
Methods: The efficacy, rapidity of detection, and cost-effectiveness of KOH preparation, calcofluor white (CW) stain, and Chicago sky blue (CSB) stain in the identification of fungal elements were assessed in patients with dermatophytoses attending the dermatology clinic of a tertiary care hospital. All three tests were performed on each sample collected from 73 patients according to standard procedure. The slides were examined after 5 and 30 minutes in × 10 and × 40 magnifications. The sensitivity and specificity of CW and CSB at 5 and 30 minutes were calculated using KOH preparation as the standard test.
Results: CSB stain showed highest positivity (94.5%) within 5 minutes when compared to KOH (75.3%) and CW (83.5%). After 30 minutes, positivity increased in KOH (84.9%) and CW stains (89%), but it remained the same in CSB stain. Both CW and CSB stains when compared to 10% KOH are equally sensitive (100%), but CW was more specific (72.7%), particularly at 30 minutes. When cost of performing tests on 100 specimens is considered, KOH, CW, and CSB stains cost Rs 5, 100, and 15, respectively.
Conclusion: CSB stain is a better stain for rapid diagnosis of dermatophytoses because of ease of performance, rapidity of detection, better appreciation of morphology of fungal elements, and cost effectiveness.
(© 2016 The International Society of Dermatology.)