Background: To create awareness for mismeasurements of ion-selective electrodes caused by patients' medications and to prevent severe consequences in an intensive care therapy.
Case presentation: 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.
Conclusions: The substance sodiumperchlorate, which is well established in Europe for hyperthyreosis therapy, caused malfunctions of analyses of ionised calcium by POCT systems.