Reproducibility of a quantitative cutaneous cytological technique

BACKGROUND: Cutaneous cytology is a valuable tool for diagnosis of canine superficial pyoderma. Current published reproducible techniques are semiquantitative. HYPOTHESIS/OBJECTIVES: The aim of this study was to evaluate the reproducibility of a quantitative method for skin surface cytology in dogs with superficial pyoderma. ANIMALS: Impression smears were collected from five normal dogs and 20 dogs with clinical and cytological evidence of superficial pyoderma. METHODS: Four investigators evaluated 10 oil immersion fields (OIF) on 25 slides, selecting fields with inflammatory cells, nuclear streaming and or keratinocytes under ×10 magnification. Investigators repeated blinded evaluations of all slides at least twice. For each OIF, polymorphonuclear leukocytes (PMNs), intracellular (IC) cocci, extracellular (EC) cocci, IC rods, EC rods and yeast were quantified. Nuclear streaming was scored as present or absent. For each parameter, within‐reader and between‐reader agreements were expressed by the intraclass correlation (ICC) value (≤0.20 poor, 0.21–0.40 fair, 0.41–0.60 moderate, 0.61–0.80 good and 0.81–1.00 excellent) or kappa statistic (κ). RESULTS: Reproducible parameters included: PMNs (ICC = 0.58), nuclear streaming (ICC = 0.68), EC cocci (ICC = 0.64) and IC cocci (ICC = 0.32). When qualified as present or absent, within‐reader κ for IC cocci was 0.71. The method demonstrated 93% sensitivity in identifying dogs with superficial pyoderma and 51% specificity in identifying normal dogs according to established criteria. However, if criteria for normal dogs were limited to the absence of PMNs and IC bacteria, sensitivity of 64% and specificity of 98% were demonstrated. CONCLUSIONS AND CLINICAL IMPORTANCE: For several parameters, including PMNs, nuclear streaming, EC cocci and IC cocci, a reproducible, quantitative cytological technique was identified.