A-127 Stability of Ionized Calcium in Blood Gas Specimens

Background Ionized calcium monitoring is crucial for monitoring critically ill patients as well as patients undergoing apheresis. According to CLSI C31-A2:2001, the acceptable stability time for all tests to be run on blood gas analyzers in heparinized syringes is thirty minutes from collection. We sought to determine whether the stability of ionized calcium in blood gas samples can be extended to accommodate prolonged transport times. Methods Sixty whole blood samples were collected into 1CC syringes containing 23 IU of heparin (Vital Signs, Inc.) and sent to the laboratory for ionized calcium and pH analysis on the Siemens RAPIDLab 1265. If the remaining sample was sufficient, it was set aside for additional testing 40, 60 and 90 minutes after receipt in the laboratory. All samples were kept at room temperature during all timepoints. The three timepoints were compared to the initial reported baseline result and the average percent bias and standard deviation was determined. Results When compared to the baseline result, samples analyzed at the 40-, 60-, and 90-minute timepoints showed negligible bias for both pH and ionized calcium. The absolute bias was within +/- 0.6 and +/-0.4 for ionized calcium and pH, respectively. Conclusions This study showed that accurate measurements of both ionized calcium and pH can be obtained from blood gas samples collected in heparinized syringes at least till 90 minutes after collection.