Antithrombin III (ATIII) activity in plasmas from normal and diseased horses, and in normal canine, bovine and human plasmas.

Plasma Antithrombin III (ATIII) activity was quantitated in 24 clinically normal Standardbred/Thoroughbred horses using a clotting time technique. ATIII activity ranged from 80 to 106% of the pooled reference standard plasma, with a mean of 94%. Horses presenting with impaction or spasmotic colic (n=17) had normal plasma ATIII activity, while 15 horses presenting with acute diarrhea/colitis had significantly lower plasma ATIII activity with a mean of only 74% of the reference plasma. Seven horses presenting with liver disease had significantly higher plasma ATIII activity with a range of 127 to 177% of the pooled reference plasma. Fifty-seven equine plasmas were retested using a rapid chromogenic substrate technique for quantitating plasma ATIII activity. A good correlation (r =+0.83) existed between clotting time and chromogenic determinations of ATIII. Pooled normal canine, human and bovine plasmas had only 65, 62 and 79%, respectively, of the ATIII activity of the equine reference plasma.