Evaluation of radiometer ICA1 as a routine instrument for serum ionized calcium and its application for whole blood capillary samples from newborn infants.

The Radiometer ICA1 was evaluated with four sets of samples: a) 289 serum samples sent for routine analysis of ionized calcium, b) a reference set of serum samples from 40 healthy laboratory workers, c) 42 capillary whole blood samples from healthy full-term and d) six capillary whole blood samples from pre-term infants. For comparison, all sets except the capillary samples were also run on the Orion SS-20. The ICA1 gave higher readings than the Orion SS-20 for normo-(mean difference 0.011 mmol/l) and hypocalcaemic (mean difference 0.037 mmol/l), but not for hypercalcaemic serum samples. The mean +/- 2 SD range for the serum reference set was 1.15-1.31 mmol/l for ICA1 and 1.14-1.27 mmol/l for Orion SS-20. The within-assay and between-assay precision were 0.014 and 0.032 mmol/l (SD) respectively for ICA1 and 0.010 and 0.022 mmol/l (SD) for Orion SS-20. The 42 healthy full-term infants had a mean +/- 2 SD range of 1.18-1.47 mmol/l. The six pre-term infants had whole blood ionized calcium 0.82-1.07 mmol/l. Three of them had ionized calcium less than 0.90 mmol/l and a symptomatic hypocalcemia.