Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing

The effects of 3.2% and 3.8% sodium citrate concentration on the results of routine coagulation assays (prothrombin time [PT] and activated partial thromboplastin time [aPTT]) were evaluated by means of two sets of reagents, one responsive and the other nonresponsive. Five groups were entered in the study: healthy volunteers; outpatients receiving stable oral anticoagulant therapy; and hospitalized patients receiving intravenous (i.v.) heparin therapy, both i.v. heparin and oral anticoagulant therapy, or no anticoagulant therapy. With use of nonresponsive PT and aPTT reagents, varying the citrate concentration has little clinical significance except in patients receiving i.v. heparin therapy. In contrast, when responsive PT and aPTT reagents are used, the concentration of sodium citrate anticoagulant has a significant effect on assay results. Eighteen percent of samples from patients receiving stable oral anticoagulant therapy demonstrated a change of less than 0.7 INR (International Normalized Ratio) units between citrate concentrations. Nineteen percent of patients receiving i.v. heparin therapy had a greater than 7-second difference when aPTT results were compared. These data demonstrate that citrate concentration affects the results of coagulation tests. On the basis of these data, it is recommended that 3.2% citrate be used for all coagulation tests.