Determination Of Antithrombin III In Extravasal Body Fluids By Radioimmunoassay

Detection of trace amounts of AT III need highly sensitive methods like a radioimmunoassay. Purified human AT III was radiolabeled enzymatically with the GOD/POD method. After iodination, the 125 J-AT III was purified by affinity chromatography over heparin agarose. The antibody (rabbit immunoglobulin) was adsorbed to protein A-Sepharose and covalently linked by dimethyl suberimidate. Binding capacity of the radioiodi- nated AT III was >90%. The sensitivity of the immunoassay was 20 ng/ml AT III. The intercept point (50% displacement) was at 300 ng/ml AT III. Healthy volunteers with a renal excretion of < 50 mg/24 hours total protein had an AT III excretion of 30 - 50 ug/24 hours.

< 50 mg/24 hours total protein had an AT III excretion of 30 - 50 ug/24 hours.

Spinal fluid within the normal range of 150 - 450 mg/1 total protein contains 0.5 - 2.5 mg/1 AT III.

Patients undergoing continous ambulant peritoneal dialysis (CAPD) lost 2.5 - 12 g protein with up to 4×1.5 - 2 l dialysate. The loss of AT III was 20 - 100 ng/24 hours.