PREANALYTICAL PROCEDURES IN THE MEASUREMENT OF IONIZED CALCIUM IN SERUM AND PLASMA

To investigate the effects of sampling routines, ionized calcium (corr ected for pH) was measured after sampling in different types of tubes and under fasting and postprandial conditions. The results are discuss ed with respect to analytical goals. Serum samples, collected in vacuu m tubes and spun after coagulation, could be safely measured during 24 h. This time window was expanded to 48 hours by using gel-containing tubes. Properly prepared specimens withstand mail transportation. Diff erent brands of gel-containing tubes gave different results, and these differences were clinically significant. An ''American-type'' breakfa st causes an average decrease of corrected ionized calcium ion concent ration of 0.04 mmol/l and an increased interindividual variation of re sults. Characterisation of reference intervals should include the ''nu tritional status'' and the brand of vacuum tube used.