DiaPharma Group, Inc.

Intended use

A chromogenic kit for the quantitative determination of the heparin cofactor activity of antithrombin (AT) in human citrated plasma. The use of factor Xa in preference to thrombin eliminates interference from heparin cofactor II and thrombin inhibitors.

Summary and principle

Antithrombin is the most important natural inhibitor of the coagulation cascade. By inhibiting the coagulation proteases, especially thrombin, factor Xa, and factor IXa, antithrombin prevents uncontrolled coagulation and thrombosis. Plasma is incubated with an excess of Factor Xa (FXa) in the presence of heparin. The residual activity of FXa is determined by the rate of hydrolysis of the chromogenic substrate S-2772. The pNA release measured at 405 nm is inversely proportional to the AT level in the range 10-125% of normal plasma.

Measurement principle

Reagent -- Composition, Packaging, Storage and Stability

Substrate S-2772, 26 mg 2 vials Lyophilized chromogenic substrate (Ac-D-Arg-Gly-Arg-pNA·2HCl). Stability after reconstitution 6 months at 2-8°C in the original vial.

Buffer with heparin, 25 mL 6 vials Tris buffer, pH 8.2, ionic strength 0.25.

Factor Xa, 90 nkat 6 vials Contains purified bovine Factor Xa and bovine albumin. Stability when opened 3 months at 2-8°C in the original vial. Stability after reconstitution 3 months at 2-8°C in the original vial.

Unopened reagents are stable until the expiration date shown on the vial when stored at 2-8°C. WARNING: Do not use reagents beyond the expiry date printed on the package label. Discard if the substrate solution appears yellow.

Additional reagents and control plasmas

1. Deionized water, filtered through 0.22 mm or NCCLS type II water.1
2. Calibration plasma
3. Control Plasma Abnormal
4. Control Plasma Normal
5. Saline (0.9% NaCl)