Use of Potassium Concentrations as a Quality-of-Service Metric for Phlebotomists Detects Systematic Preanalytical Biases and Facilitates Their Correction

To the Editor:The detection and monitoring of preanalytical bias in the clinical laboratory can be challenging, as bias can be introduced at any point from specimen collection to sample processing, and those biases stemming from sample collection or handling before delivery to the laboratory can be difficult to measure and eliminate. In particular, variations in potassium concentrations due to preanalytical sources of error are a pervasive and clinically significant problem (1–3).Initial concern regarding spuriously increased potassium concentrations (>5.2 mmol/L) occurring in the laboratory of the Dana Farber Cancer Institute was raised by clinicians reporting patients displaying increased potassium without any apparent clinical justification. Review of the medical records of the patients involved demonstrated that the majority had potassium values within the reference interval on the draw before the increased value, with a mean increase in potassium of 1.2 (0.7) mmol/L vs the prior value. Retesting on an alternative platform confirmed hyperkalemia. To assess for a preanalytical cause of these values, samples were redrawn on the same day …