A novel proficiency test to assess the animal diagnostic investigation process in identifying an unknown toxicant

Participation in Proficiency Tests (PTs) is an important component of quality assurance in testing laboratories. In a typical chemistry PT, blind-coded samples are sent to participants for analysis of specific chemical agents, and results are compared to a pre-determined key (e.g., expected concentrations) to assess proficiency. In the animal diagnostic PT presented here, organizers evaluated not only the analytical component of the diagnostic investigation but also the entire investigative process as a multi-step, holistic multidisciplinary approach. Fourteen veterinary diagnostic laboratories (VDLs) participated in an exercise to identify the root cause of a simulated case of lead (Pb) toxicosis. VDLs received a case description outlining neurological signs in cattle, a digitized brain histology slide, and liver and brain tissue samples for optional chemistry analysis. Thirteen of 14 VDLs successfully diagnosed lead toxicosis by completing the following stages: (a) correctly identifying histological abnormalities, (b) providing three adequate differential diagnoses, (c) selecting adequate chemistry analyses to rule in or rule out possible causes, (d) accurately detecting lead concentration in the liver, and (e) interpreting the diagnostic significance of their results correctly. Importantly, participants first had to determine which chemistry analyses were appropriate and then to accurately quantify the target analytes. This approach provided greater confidence in the diagnostic capability of the laboratory by reducing the bias associated with being given a known chemical contaminant for which to test, typical of most chemistry PTs, and may therefore be of interest to PT providers and accreditation committees.