Enzyme-linked immunosorbent assay for thrombin-antithrombin III complexes in horses

To adapt and characterize a human ELISA kit to quantify thrombin-antithrombin III (TAT) complexes in horses, and to evaluate TAT as a marker for hypercoagulation in horses.

29 clinically normal horses used as controls, and 4 ill horses used to evaluate assay for known causes of hypercoagulation.

A commercially available human sandwich-type ELISA kit with 2 antibodies against human thrombin and antithrombin III that bind selectively to their corresponding TAT antigenic sites was used. Equine TAT standards were made from purified equine thrombin and antithrombin III. Proteins diluted in a phosphate-buffered saline solution containing 0.1% Tween and 1 U of heparin/ ml were used to establish standard curves. Reference intervals for TAT concentration in citrated equine plasma, and intra- and interassay coefficients of variation were determined.

Mean +/- SD values were 3.95 +/- 1.93 micrograms/L, with median of 3.18 micrograms/L and range of 1.95 to 9.03 micrograms/ L. One horse with cecal perforation had TAT concentration of 174.30 micrograms/L, and a horse infused IV with endotoxin had TAT concentration of 62.98 micrograms/L 12 hours after infusion.

The data suggest that human TAT ELISA kits can be used to measure TAT concentration in citrated equine plasma, and that TAT is a marker for hypercoagulation in horses.

Assays for equine TAT many help to further characterize the hypercoagulable state in horses.