sodium-perchlorate and Hypocalcemia

To create awareness for mismeasurements of ion-selective electrodes caused by patients' medications and to prevent severe consequences in an intensive care therapy.. A 73-year-old woman presented with severe carbimazol-induced toxic epidermal necrolysis. After replacement of carbimazol by sodiumperchlorate, we detected a huge discrepancy in the measurement of ionised calcium by two different Point-of-Care (POCT) systems. While Siemens Rapidlab 865 showed a severe hypocalcemia at all times, the Radiometer 600 system first presented a severe hypercalcemia and, in the course of the following days, also a hypocalcemia but with significantly (p < 10 to the -45) higher values than the Rapidlab system. Furthermore, the POCT systems detected a pseudohypocalcemia at times where we think there was a normo- or even hypercalcemia which led to incorrect therapy with excessive substitution of ionised calcium.. The substance sodiumperchlorate, which is well established in Europe for hyperthyreosis therapy, caused malfunctions of analyses of ionised calcium by POCT systems.

Topics: Aged; Antithyroid Agents; Artifacts; Blood Chemical Analysis; Calcium; Diagnostic Errors; False Positive Reactions; Female; Humans; Hypocalcemia; Perchlorates; Point-of-Care Systems; Sodium Compounds

Blood gas analysis (BGA), including measurement of ionized calcium, is performed routinely in patients with end stage renal disease on renal replacement therapy, especially when using citrate for regional anticoagulation. After installation of a new blood gas analyzer (RAPIDpoint 405; BGA), we observed lower ionized calcium concentrations in a few patients without signs of hypocalcemia, whereas calcium concentrations were normal using a standard laboratory method. Pseudohypocalcemia was of limited duration and correlated with the short-term intake of sodium perchlorate monohydrate (Irenat).. We prepared dilution series from whole blood samples and stock solutions of calcium and perchlorate with different concentrations of ionized calcium and perchlorate. Measurement of ionized calcium concentrations was performed using two different blood gas analyzers (RAPIDpoint 405; BGA and Roche AVL 9180; standard laboratory method).. After addition of different amounts of perchlorate, significant lower ionized calcium concentrations were measured with BGA compared to the standard laboratory method using either preparations from whole blood samples or stock solutions. The addition of potassium or methylene blue known to complex perchlorate had no effect on the concentrations of ionized calcium measured with BGA. Using different mathematical methods, a calculation of the "real" ionized calcium concentration from the value measured with BGA was not possible.. Based on our experiments, we confirm the hypothesis that perchlorate can influence the measurement of ionized calcium by BGA. As the effect depends on the ion selective electrode that is used, it is advisable to test the blood gas analyzer with calcium and perchlorate solutions.

Topics: Blood Gas Analysis; Calcium; False Positive Reactions; Humans; Hypocalcemia; Kidney Failure, Chronic; Perchlorates; Sodium Compounds