EFFECT OF 3.2-PERCENT VS 3.8-PERCENT SODIUM-CITRATE CONCENTRATION ON ROUTINE COAGULATION-TESTING

The effects of 3.2% and 3.8% sodium citrate concentration on the resul ts of routine coagulation assays (prothrombin time [PT] and activated partial thromboplastin time [aPTT]) were evaluated by means of two set s 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 (IV) heparin therapy both IV heparin and oral anticoagula nt therapy, or no anticoagulant therapy. With use of nonresponsive PT and aPTT reagents, varying the citrate concentration has little clinic al significance except in patients receiving IV heparin therapy. In co ntrast, when responsive PT and aPTT reagents are used, the concentrati on of sodium citrate anticoagulant has a significant effect on assay r esults. Eighteen percent of samples from patients receiving stable ora l anticoagulant therapy demonstrated a change of less than 0.7 INR (In ternational Normalized Ratio) units between citrate concentrations. Ni neteen percent of patients receiving IV heparin therapy had a greater than 7-second difference when aPTT results were compared. These data d emonstrate that citrate concentration affects the results of coagulati on tests. On the basis of these data, it is recommended that 3.2% citr ate be used for all coagulation tests.