Improved assay conditions for automated antithrombin III determinations with the chromogenic substrate S-2238.
Assays for antithrombin III activity using the chromogenic substrate S-2238 were automated in various modifications on various instruments. Standard curves for the assay showed a deviating "0% point" in several but not all modifications. Addition of polyethylene glycol 6000/8000 (0.40-1.0%) minimizes this deviation. However, the deviation of the 0% point was not completely abolished in every modification of the test. Examination of Lineweaver-Burk plots showed nonlinearity at high concentrations of S-2238 as used in the antithrombin III assays. Addition of Tween-80 (0.01%) restores the Lineweaver-Burk plot and, at the same time, the standard curve in the assays is found to be linear. Therefore, we recommend the use of PEG 6000/8000 as well as Tween-80 in automated assay systems.
D000990:Antithrombin III / Q000032:analysis*; D002863:Chromogenic Compounds; D004151:Dipeptides; D006801:Humans; D011092:Polyethylene Glycols; D011136:Polysorbates
D002863:Chromogenic Compounds; D004151:Dipeptides; D011136:Polysorbates; D011092:Polyethylene Glycols; C021129:S 2238; D000990:Antithrombin III