The Utility of Tissue Microbiology Studies in Diagnosis and Management of Suspected Dermatological Infection

Abstract

Purpose: Skin tissue microbiology studies are often sent alongside skin biopsies for histology when evaluating patients with suspected skin infections. However, microbiology studies may require a second biopsy and are associated with laboratory time, cost and risk for additional patient discomfort and procedure complication. In this study, we evaluate the frequency in which these studies return positive or influence diagnosis/management in the general dermatology population. Methods: We randomly selected a sample of 150 patients with complete clinical documentation meeting inclusion criteria for whom both pathology and microbiology studies were ordered on skin biopsies by dermatologists at Brigham & Women's Hospital and Massachusetts General Hospital from 2000-2015. Chart review was conducted and each set of microbiology results was defined as a true/false positive/negative based on documented final clinical interpretation. Microbiology sets were categorized based on the positive result interpretation (eg: a hypothetical set with true negative bacterial culture, false positive gram stain, true positive AFB culture, true negative fungal stain and culture would be categorized as a true positive). Results: We found that microbiology studies had a sensitivity of 80.8% (confidence interval: 67.0%-89.9%), specificity of 59.2% (48.8%-68.9%), positive predictive value of 51.2% (40.0%-62.3%), and negative predictive value of 85.3% (74.2%-92.3%) for identifying infection. Microbiology studies altered diagnosis in 48.0% (n=72) of cases and led to management changes in 26.7% (n=40) of cases. Conclusions: We conclude that although microbiology studies have a relatively low yield of true positive results (n=42, 28%), they have high sensitivity and negative predictive value and lead to changes in clinical diagnosis and management. This data serve to guide clinical practice and as the basis for evaluation of the cost-effectiveness of this practice.