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Thromb Haemost 1988; 60(02): 193-198
DOI: 10.1055/s-0038-1647028
Original Article
Schattauer GmbH Stuttgart

An Approach to Assigning In Vitro Potency to Unfractionated and Low Molecular Weight Heparins Based on the Inhibition of Prothrombin Activation and Catalysis of Thrombin Inhibition

F A Ofosu
The Canadian Red Cross Society, Blood Transfusion Service, Hamilton, and The Department of Pathology, McMaster University, Hamilton, Canada
,
L M Smith
The Canadian Red Cross Society, Blood Transfusion Service, Hamilton, and The Department of Pathology, McMaster University, Hamilton, Canada
,
N Anvari
The Canadian Red Cross Society, Blood Transfusion Service, Hamilton, and The Department of Pathology, McMaster University, Hamilton, Canada
,
M A Blajchman
The Canadian Red Cross Society, Blood Transfusion Service, Hamilton, and The Department of Pathology, McMaster University, Hamilton, Canada
› Author Affiliations
Further Information

Publication History

Received 28 July 1987

Accepted after revision 18 May 1988

Publication Date:
28 June 2018 (online)

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Summary

Unfractionated and low molecular weight (LMW) heparins with good antithrombotic activity invariably catalyze thrombin inhibition and inhibit the appearance of thrombin activity in contact-activated plasma. Conversely, the antithrombotic efficacy of LMW heparins decreases as their ability to catalyze thrombin inhibition and to inhibit the appearance of thrombin activity in plasma decrease. The activated partial thromboplastin time (APTT) has proven a reliable test for assaying unfractionated heparin. We therefore compared 2 unfractionated and 3 LMW heparins on the basis of the minimum concentrations required to double the APTT of normal plasma and by then determined how this anticoagulant effect was achieved. The amount of unfractionated and LMW heparin which doubled the APTT was found to be equivalent to —0.25 antithrombin units. This concentration of each glycosaminoglycan completely inhibited prothrombin activation for 45 s after CaCl2 was added to contact-activated plasma; accelerated thrombin inhibition by purified antithrombin III by approximately 50-fold; and accelerated thrombin inhibition equally by anti thrombin III in undiluted plasma. This concentration of the three LMW heparins increased, by approximately 70fold, the rate of factor Xa inhibition by purified antithrombin III compared to the 50-fold increase seen with the two unfractionated heparins. These results thus suggest that tests based on the inhibition of prothrombin activation and/or on the catalysis of thrombin inhibition provide a useful basis for assigning in vitro potency to both unfractionated and LMW heparins.

Keywords

Heparin - Low molecular weight heparin - Anti-factor Xa
 

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