1995 OPEN FORUM Abstracts
Determinations Of Ionized Calcium/Electrolytes In Blood Gas Syringes
Virginia M. Haver, Ph.D., William E. Eng, M.T., John D. Hussey MBA. RRT, Daniel D. Bankson, Ph.D., Sambasiva Lakshminarayan, M.D., VA Medical Center, Seattle WA.
Since heparin binds calcium, either an electrolyte balanced syringe or one with minimal amounts of heparin must be used to obtain accurate values for ionized calcium (ionCa), sodium (Na) and potassium (K) in whole blood determinations. We evaluated 3 commercially available heparinized syringes: a) Radiometer (RD) Smooth-E "balanced" syringe #4900 with 120IU lyophilized heparin in 3 ml; b) Martell (MT) "balanced" syringe #30APH with 50 units blended lyophilized lithium and zinc heparin in 3 ml; c) Becton-Dickinson (BD) syringe, Bard Parker liquihep II containing 500 USP lithium heparin in 5 ml. Following informed consent, blood samples were obtained from 13 normal volunteers (forearm vein) and 8 critically ill patients in ICU's (arterial lines) into the heparinized RD and BD tubes, as well as a BD Vacutainer SST gel tube. Whole blood ionized calcium and electrolytes were assayed on a Ciba-Corning Model 288 analyzer and compared with the corresponding serum specimens from the vacutainer samples. Results were assessed by one-way analysis of variance (ANOVA), using p < 0.05 as being statistically significant. The BD syringe displayed a statistically significant lowering of ionCa values in whole blood specimens, compared to serum samples having no anticoagulant (values decreased by 0.1 mmol/L). Na and K values obtained from BD syringes were less affected ( < 3 mEq/L and< 0.2 mEq/L differences, resp.). The RD and MT syringes exhibited no statistically significant changes in ionCa, Na and K relative to serum ( < 0.02mmol/L,< 2 mEq/L andɘ.2 mEq/L differences, resp.). Blood gas determinations (pH, pO2, pCO2) were not different with all three heparinized syringes. We conclude that the BD syringe causes falsely low ionCa results because of its high heparin content. No clotting problems were observed with either the RD or MT syringes, despite their lower heparin concentration. The latter two can be used to accurately assess whole blood electrolytes and ionized calcium.