A Clinical Comparison Of Chromogenic, Fluorometric, And Natural (Fibrinogen) Substrate Assays For Determination Of Antithrombin-III

Antithrombin-III (AT-III) is a key modulator of hemostas- sis; decreases are thought to be associated with thrombosis, and the degree of decrease is thought to be indicative of severity of an intravascular clotting process. The popularity of AT-III determinations has been associated with the development of several different methodologies. To assess the clinical applicability of these different methodologies, chromogenic (Abbott), fluorometric (Dade), and fibrinogen (Cutter) substrate assays were performed on 84 individuals with disseminated intravascular coagulation (DIC) or intravascular thrombosis (DVT, PE). Severity of the intravascular coagulation or thrombosis was clinically graded as 1 through 6 by one observer; thromboscintograms were used to confirm the clinical impression: single calf thrombosis = 1, DIC = 6. Multiple linear regression analyses were performed to correlate assay resus with clinical severity of disease. All patients were expected to have abnormally low AT-III levels because of documented intravascular thromboses. However, three were normal by the fluorometric assay, 26 were normal by the chromogenic assay, and 12 were normal by the fibrinogen-substrate assay. When comparing assays the correlations were as follows: Cutter vs. Dade: r=0.70; Cutter vs. Abbott: r=0.70; Dade vs. Abbott: r=0.64. When correlating the assay method with severity of intravascular coagulationAihrombosis the following was found: Cutter: r=0.44, Dade: r=0.76, and Abbott: r=0.43. The means and standard deviations for the entire population are as follows: Cutter = 79.8 ∓ 29.2, Dade = 79.0 ∓ 19.8, and Abbott = 102.0 ∓ 30.2. Based upon this study the most clinically applicable and useful assay appears to be the fluorometric method (Dade). Because of diagnostic accuracy, automation, and ease of performing the assay this is the recommended method and, therefore has been the assay adopted in our laboratory for routine clinical use.