Erroneous Patient Tissue Contaminants in 1574 Surgical Pathology Slides

Context.-Tissue contaminants on histology slides rep-resent a serious risk of diagnostic error. Despite their pervasive presence, published peer-reviewed criteria de-fining contaminants are lacking. The absence of a standardized diagnostic workup algorithm for contami-nants contributes to variation in management, including investigation and reporting by pathologists. Objective.-To study the frequency and type of tissue contaminants on microscopic slides using standardized criteria. Using these data, we propose a taxonomy and algorithm for pathologists on "floater"management, includ-ing identification, workup, and reporting, with an eye on patient safety. Design.-A retrospective study arm of 1574 histologic glass slides as well as a prospective study arm of 50 slide contamination events was performed. Using these data we propose a structured classification taxonomy and guide-lines for the workup and resolution of tissue contamination events. Results.-In the retrospective arm of the study, we identified reasonably sized benign tissue contaminants on 52 of 1574 slides (3.3%). We found size to be an important parameter for evaluation, among other visual features including location on the slide, folding, ink, and tissue of origin. The prospective arm of the study suggested that overall, pathologists tend to use similar features when determining management of potentially actionable con-taminants. We also report successfully used case-based ancillary testing strategies, including fluorescence in situ hybridization analysis of chromosomes and DNA finger-printing. Conclusions.-Tissue contamination events are underre-ported and represent a patient safety risk. Use of a reproducible classification taxonomy and a standardized algorithm for contaminant workup, management, and reporting may aid pathologists in understanding and reducing risk.