Preparation and use of serum-based material as control and calibrator in evaluating ion-selective electrodes for calcium.
We analyzed 93 sera and 81 whole-blood samples, plus several aqueous materials and one serum-based material as controls, with two analyzers for ionized calcium (Radiometer ICA 1 and AVL 980). On 16 days, comparisons of results for patients' samples were good, with nearly all between-instrument differences (delta Ca2+) of samples being within 0.04 mmol/L. On 12 days, comparisons were mediocre, with the delta Ca2+ of samples usually 0.04 to 0.10 mmol/L. The control material that most consistently indicated the direction and magnitude of the delta Ca2+ of patients' samples was the serum-based control. Adjustment of results for samples from patients, based on the delta Ca2+ of the serum control on the same day, substantially improved comparisons between instruments. Our findings suggest that the use of a serum-based calibrator provides the most valid comparison between different calcium-ion analyzers and reliably indicates when electrode replacement is needed.
D001322:Autoanalysis / Q000295:instrumentation; D002118:Calcium / Q000097:blood*; D004566:Electrodes; D006801:Humans; D012016:Reference Values; D013997:Time Factors
D002118:Calcium