Korean J Clin Pathol.
1997 Feb;17(1):34-40.
The Significance of Sample Preparation in Measurement of Ionized Calcium
Abstract
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BACKGROUND: Calcium status is more accurately determined by measuring free calcium, the tightly regulated biologically active form. The concentration of ionized calcium is strongly dependent on different preanalytic factors. In this study the influence of several methodological factors on the concentration of ionized calcium in blood is investigated.
METHODS
Authors selected 127 persons of health care management center & comparatively healthy-look, out-patients of our hospital. When serum was needed, blood was anaerobically withdrawn in vacutainers, the serum was separated after standing at room temperature. For the plasma sample blood was anaerobically drawn into the tube with dry sodium heparin 143 IU/10ml blood in the same patient. And then, to avoid CO2 loss, the samples were left unopened and centrifuged anaerobically at 900g for 15 min; the serum and plasma were then pipetted as quickly as possible into 2ml plastic eppendorf-tube, which were completely filled and sealed off immediately and keeping it in refrigeration before testing. For the studies of calcium binding effect by different volume of sodium heparin. blood was collected into two type of tube, each containing 30IU heparin/whole blood ml or 125 IU/ml. Ioniged calcium were measured by ion-selective electrodes.
RESULTS
1. The reference value of ionized calcium in serum and plasma was 4.9+/- 0.19, 4.9+/-0.17 mg/ml(serum versus plasma, p>0.05) respectively. 2. The concentration change of ionized calcium according to heparin volume shows no significant difference until heparin 14.3 IU/blood 1 ml compared with serum. 3. The concentration of ionized calcium of serum and plasma was stable until 4 hours and 4 days after serum and plasma separation.
CONCLUSIONS
Above shows that the concentration of ionized calcium have the same reference range on both serum and plasma. But each laboratory should have their own reference range according to heparin volume, ionized calcium in serum and plasma samples kept at -4degrees C remains stable within few days, provided the proposed conditions for storage.
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