Accuracy of Electrolyte and Blood Gas Determinations from Samples Collected in Preheparinized Syringes

BACKGROUND: We sought to determine whether commercially prepared, heparinized syringes provide accurate results for both blood gas and electrolyte analysis of whole-blood samples. Because of heparin binding, either an electrolyte-balanced syringe or one containing only minimal amounts of heparin must be used to ensure accurate values for electrolytes in whole-blood determinations. METHODS & MATERIALS: We evaluated 3 commercially available heparinized syringes: (1) Becton Dickinson (BD) standard 5-mL liquid-heparin syringe, 100 units lithium-heparin/mL, (2) Radiometer electrolyte-balanced heparin 3-mL syringe (EB-R), containing Ca++-, Nat-, and K+-heparin in lyophilized form, 40 units/mL; and (3) Martell electrolyte-balanced heparin 3-mL syringe (EB-M), containing Li- and Zn-heparin in lyophilized form, 16.7 units/mL. Blood samples from 13 normal volunteers and 8 critically ill ICU patients were drawn into BD, EB-R, and EB-M syringes and into BD SST gel tubes (control). Blood was assayed on a Ciba-Corning Model 288 analyzer, and values for Ca++, Na+, and K+ were compared with values obtained from the corresponding serum specimens from the vacuum tubes. Results were assessed by 1-way analysis of variance (ANOVA), with p < 0.05 considered statistically significant. RESULTS: Whole-blood specimens collected in the BD syringe yielded values for Ca++ that were statistically significantly lower than serum values from samples containing no anticoagulant (values decreased by 0.1 mmol/L). Nat and K+ values obtained from BD syringes were less affected. (Nat values differed by <3 mEq/L and K+ values < 0.2 mEq/L.) Results of analysis of whole-blood samples collected in EB-R and EB-M syringes did not differ significantly from results obtained from analysis of serum specimens (difference for Ca++ < 0.02 mmol/L, for Na+ < 2 mEq/L, and K+ < 0.2 mEq/L). Blood gas determinations were not different among the 3 heparinized syringes. No clotting problems were observed with either the EB-R or EB-M syringes. CONCLUSIONS: We conclude that collection in the BD syringe leads to falsely low Ca++ results because of the syringe's high heparin content. The EB-R and EB-M syringes can be used to accurately assess whole-blood Na+, K+, and Catt.