Preanalytical potassium EDTA sample contamination: open versus closed phlebotomy systems

Abstract

Background Potassium ethylenediaminetetraacetic acid (K-EDTA) contamination of serum samples is a common cause of spurious electrolyte results, which may adversely affect patient care. The source of K-EDTA sample contamination is unknown since it is not caused by reverse order of draw. Other possible mechanisms are either direct transfer of blood from K-EDTA containing tubes to other tubes or syringe needle/top contamination when delivering blood into EDTA sample tubes before other sample tubes, but these have not been studied in clinical practice. We report on a quality improvement programme aimed at identifying the source of K-EDTA-contaminated samples. Methods We routinely measure EDTA in all serum samples with a potassium ⩾6.0 mmol/L. We identified individuals responsible for K-EDTA-contaminated samples (EDTA >0.15 mmol/L) and in close-to-real-time discussed their phlebotomy methods for the collection of these samples. Results Over four months, we investigated 96 EDTA-contaminated samples. Of these, we identified and interviewed 64 (67%) individuals responsible for contaminated samples; 52 (81%) doctors, 9 (14%) phlebotomists and 3 (5%) nurses. Fifty-two individuals recalled taking the sample and the phlebotomy method used. All used open phlebotomy methods. Conclusions We report, for the first time, that K-EDTA sample contamination almost always, if not exclusively, occurs following open phlebotomy methods. Phlebotomy training and guidelines should, therefore, encourage use of closed systems as well as include and emphasize the importance of ‘order of blood sample tube fill’ when using open phlebotomy methods.