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September 28, 1979

Antithrombin III Assays

Author Affiliations

Institute of Rehabilitation Medicine New York University Medical Center New York

JAMA. 1979;242(13):1360-1361. doi:10.1001/jama.1979.03300130014005

To the Editor.—  In a letter to the editor, Roger L. Bick, MD (239:296, 1978), commented on the clinical determination of antithrombin III, pointing out the usefulness of chromogenic substrate and that an increased predisposition to thromboembolic phenomena is associated with a decreased antithrombin III level. In reply, Harry L. Messmore, MD, and Jawed Fareed, PhD (240:345, 1978), questioned the use of autolytic forms of thrombin and the chromogenic substrate in the antithrombin III assay.The methods employed for antithrombin III assay can be roughly classified into two categories: immunological and functional. There are two types of functional assays available: the rate determination procedure and the end-point analysis. The rate of the inhibition of thrombin by antithrombin III depends on (1) the amount of antithrombin III present, (2) the amount of heparin or heparin-like substance present in the sample, and (3) the quantity of thrombin employed. It was first pointed