Interference of coumarin therapy with the "Heptest" owing to declining prothrombin concentrations.
The Heptest kit (Haemachem, Inc., St. Louis, MO) for quantifying heparin in plasma is based on heparin-mediated inhibition of factor Xa, resulting in prolongation of clotting time. In 19 of 55 plasma samples obtained from 32 patients concurrently receiving coumarin and heparin, Heptest results exceeded true heparin values by more than 0.2 int. unit/mL; four samples showed a deviation exceeding 0.4 int. unit/mL. We show here that these deviations are caused by coumarin-induced decreases of plasma prothrombin. This problem can be circumvented by adding purified prothrombin or normal plasma to the assay mixture.
Fischer
J
J
Department of Hematology, University of Nijmegen, The Netherlands.
Verbruggen
B
B
Wessels
H
H
Haanen
C
C
D003374:Coumarins / Q000627:therapeutic use*; D005189:False Positive Reactions; D006493:Heparin / Q000097:blood* / Q000627:therapeutic use; D006801:Humans; D010949:Plasma; D011516:Prothrombin / Q000097:blood*; D011933:Reagent Kits, Diagnostic
D003374:Coumarins; D011933:Reagent Kits, Diagnostic; D011516:Prothrombin; D006493:Heparin; C030123:coumarin