Repeatability and Reproducibility of Microscopic Examination of Adhesive Tape Strip Cytology Slides for the Diagnosis of Malassezia Overgrowth and/or Malassezia Dermatitis in Dogs.

Adhesive tape strip cytology at 1000× magnification is the recommended method for the presumptive diagnosis of canine Malassezia overgrowth and/or dermatitis. This study aimed to determine the minimum number of microscopic fields required to achieve optimal intraobserver repeatability and interobserver reproducibility. Two groups of cytology slides were evaluated: 12 slides paired with photographs of pruritic dogs, in which a presumptive diagnosis of Malassezia dermatitis was defined by the detection of at least one yeast organism, and eight slides paired with photographs of non-pruritic dogs, in which a presumptive diagnosis of Malassezia overgrowth and dermatitis was defined by the detection of an average of at least one yeast organism per microscopic field. Twelve investigators examined each slide twice, and results from the first 10, 20, 30, 40, and 50 oil immersion fields were recorded and used for statistical analysis. Regardless of the number of microscopic fields examined, overall intraobserver repeatability and interobserver reproducibility were clinically non-acceptable for both slide groups and did not substantially increase in parallel with the number of the fields examined. Consequently, negative adhesive tape strip cytology results may not exclude Malassezia overgrowth and/or dermatitis in dogs with compatible clinical signs.