[Antithrombin III determination in horses. Reference values and acquired antithrombin III deficiency].

Antithrombin III (AT III) determinations were done in healthy and sick horses using the chromogenic substrate Chromozym TH. Reference values for adult horses at 25 degrees C were 18-25 IU AT III per ml plasma and 84-118% AT III activity of normal horse plasma, respectively. Precision and accuracy were good (intra assay coefficient of variation less than 2%, accuracy 10%). Surgical operations on healthy horses led to a biphasic decrease in AT III activity touching the lower border of the reference values on the second postoperative day. Other reasons for acquired AT III deficiencies included disseminated intravascular coagulation (DIC), liver disease and glomerulonephritis. Using follow-up studies, differences in the dynamics of acquired AT III deficiency and coagulation promoting factors were demonstrated. 12 of 35 horses with decreased AT III values suffered from phlebothrombosis of the jugular veins. It was presumed that acquired AT III deficiencies promote development and progression of phlebothrombosis/thrombophlebitis in horses.