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

Abstract

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/1) and hypocalcaemic (mean difference 0.037 mmol/1), but not for hypercalcaemic serum samples. The mean ± 2 SD range for the serum reference set was 1.15–1.31 mmol/1 for ICA1 and 1.14–1.27 mmol/1 for Orion SS-20.

The within-assay and between-assay precision were 0.014 and 0.032 mmol/1 (SD) respectively for ICA1 and 0.010 and 0.022 mmol/1 (SD) for Orion SS-20.

The 42 healthy full-term infants had a mean ± 2 SD range of 1.18–1.47 mmol/1. The six pre-term infants had whole blood ionized calcium 0.82–1.07 mmol/1. Three of them had ionized calcium <0.90 mmol/1 and a symptomatic hypocalaemia.