Journal Article

Antithrombin III Determination in Nearly-Undiluted Plasma

Thomas W. Stief

in Laboratory Medicine

Published on behalf of American Society for Clinical Pathology

Volume 39, issue 1, pages 46-48
Published in print January 2008 | ISSN: 0007-5027
Published online September 2015 | e-ISSN: 1943-7730 | DOI:
Antithrombin III Determination in Nearly-Undiluted Plasma

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Antithrombin III (AT3) in highly diluted plasma may not react like AT3 in circulating blood.


To avoid artificial changes of the plasma matrix by strong dilution, a new AT3 test was developed: 25 μL citrated plasma reacts with 5 μL thrombin reagent, 92 IU/mL (15.3 IU/mL final) bovine alpha-thrombin, 10 IU/ml (1.7 IU/mL final) heparin, 1,480 mM (247 mM final) arginine, pH 7.4, 6% human (albumin) for 1 min (37°C). Plasma is only diluted by 20%. Then 100 μL 2.5 M arginine, 0.13% Triton X 100, and 50 μL 1 mM (0.28 mM final) chromogenic thrombin substrate CHG-Ala-Arg-pNA are added and increase in absorbance (ΔA/min) is determined.


Antithrombin III is specifically determined with 1 min reaction time; from the third minute onward a second thrombin inactivator significantly acts.


This undiluted AT3 test uses approximately 10 IU/ml (final acitivity) thrombin, which is the approximate peak activity of thrombin caused by intrinsic hemostasis activation.

Journal Article.  0 words. 

Subjects: Haematology

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