EDTA sample contamination is common and often undetected, putting patients at unnecessary risk of harm

Abstract

BackgroundPotassium ethylenediaminetetraacetic acid (EDTA) is a sample tube anticoagulant used for many laboratory analyses. Gross potassium EDTA contamination of blood samples is easily recognised by marked hyperkalaemia and hypocalcaemia (1-3). Subtle potassium EDTA contamination, however, is a relatively common often unrecognised erroneous cause of spurious hyperkalaemia (2). This has the potential to adversely affect patient care and waste healthcare resources (4,5).In addition to hyperkalaemia and hypocalcaemia, potassium EDTA contamination may also cause hypomagnesaemia (1,2) and hypozincaemia (2). There are, however, no data on the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia. We therefore audited the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia over a 1-month period. MethodsFollowing a recent service evaluation (2), we routinely measure EDTA in serum samples from patients with unexplained hyperkalaemia (serum potassium > 6.0 mmol ⁄ l).In addition, over a 1-month period EDTA concentrations were measured in hypocalcaemic (serum adjusted calcium < 2.0 mmol ⁄ l), hypomagnesaemic (serum magnesium < 0.7 mmol ⁄ l) and hypozincaemic (serum zinc < 11 lmol ⁄ l) serum samples.Blood samples for routine serum biochemistry, plasma glucose and routine haematology are respectively collected into Sarstedt serum ⁄ z4 gel tubes, S U M M A R YBackground: Potassium ethylenediaminetetraacetic acid (EDTA) is a sample tube anticoagulant used for many laboratory analyses. Gross potassium EDTA contamination of blood samples is easily recognised by marked hyperkalaemia and hypocalcaemia. However, subtle contamination is a relatively common, often unrecognised erroneous cause of spurious hyperkalaemia. Potassium EDTA contamination may also cause hypomagnesaemia and hypozincaemia. There are, however, no data on the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia. Methods: Following a recent service evaluation, we measure EDTA in serum samples from patients with unexplained hyperkalaemia (serum potassium > 6.0 mmol ⁄ l). In addition, over a 1-month period EDTA concentrations were measured in hypocalcaemic (serum adjusted calcium < 2.0 mmol ⁄ l), hypomagnesaemic (serum magnesium < 0.7 mmol ⁄ l) and hypozincaemic (serum zinc < 11 lmol ⁄ l) serum samples. Results: Ethylenediaminetetraacetic acid contamination was detected in 31 samples, nine of which were detected by our routine screening programme. The remaining 22 samples represented 14.3% (19 ⁄ 133) of hypocalcaemic samples, 4.8% (5 ⁄ 104) of hypomagnesaemic samples and 1.4% (2 ⁄ 139) of hypozincaemic samples. A total of 25 ⁄ 31 (80.6%) of patients were re-bled, of which 23 ⁄ 25 (92%) results normalised. Conclusions: Factitious hyperkalaemia, hypocalcaemia and hypomagnesaemia caused by potassium EDTA contamination in our studies are relatively common, and if unrecognised may adversely affect patient care and waste scarce healthcare reso...

Preanalytical quality improvement. In pursuit of harmony, on behalf of European Federation for Clinical Chemistry and Laboratory Medicine (EFLM) Working group for Preanalytical Phase (WG-PRE)

“…As this is not probably due to the use of a random order of draw of blood samples in a closed loop system, it seems plausible that in vitro K-EDTA and citrate contamination may occur with open blood collection systems by syringe needle or syringe tip contamination when delivering collected blood into K-EDTA or citrate sample tubes before other tubes, and by direct transfer of blood from K-EDTA or citrate containing tubes to other sample tubes [51]. The latter circumstance can be easily detected by the laboratory staff, because it would generate gross abnormalities in surrogate markers.…”

Contemporary view of the clinical relevance of magnesium homeostasis

“…30 In addition, as extracellular fluid space contains only 1% of total body magnesium, serum magnesium may not always accurately reflect the intracellular magnesium status and a subject with normal serum magnesium concentrations may have total body magnesium depletion. 3 Finally, 30% of serum magnesium is bound to albumin and is therefore inactive; as most methods of assessing serum magnesium content measure total magnesium concentration, hypoalbuminaemic states may lead to spuriously low magnesium values.…”

Variation in phlebotomy techniques in emergency medicine and the incidence of haemolysed samples

“…Such contamination can lead to erroneous results for analytes with raised potassium due to introduction into the serum tube, and reductions in calcium and magnesium and other less commonly measured metal ions due to chelation effects of EDTA. 2 However, these studies lack direct observational evidence that incorrect order of draw is commonly practised in clinical areas. Studies instead rely on measuring the presence of EDTA in samples, where high potassium or low calcium indicates the possibility of contamination.…”