Dextran and hydroxyethyl starch interfere with fibrinogen assays.

We studied the haemostatic and volume effects of synthetic plasma substitutes and Ringer's solution in 48 surgical patients and found that the measured fibrinogen concentrations of patients receiving either dextran or hydroxyethyl starch (HES) were significantly higher than those predicted by the dilutional effects. The groups given Ringer's solution showed no apparent disproportion between fibrinogen concentration and plasma volume change. The results suggested that the presence of artificial colloids might interfere with the indirect fibrinogen assay used in the study. The method of analysis was based on light scattered from the reaction mixture during prothrombin time (PT) measurement. To test the hypothesis, plasma was obtained from nine volunteers to prepare 20, 40 and 60% dilutions in normal saline, 6% dextran 70, 6% HES 120/0.7 or 6% HES 200/0.5 solutions. Fibrinogen was measured on a ACL-300R coagulometer by two indirect methods, PT derived and the Clauss method. Relative concentrations were compared by analysis of variance and Sheffé's multiple comparisons. Dilutions containing either dextran or HES gave significantly higher values (P < 0.001) than samples diluted with normal saline. We conclude that the results of indirect fibrinogen assays should be interpreted cautiously, when HES or dextran is used for volume replacement. This may be particularly true when hypofibrinogenaemia is encountered after extensive use of synthetic colloids during massive transfusion.