The anti-Xa assay is the gold standard for measuring the anticoagulant effect of heparin and its derivatives in blood. The method is automated and well established in clinical practice, but it is insufficiently standardized, which means that the measured anti-Xa values vary between the different methods used. These methods differ mainly in the presence of exogenous antithrombin and dextran sulphate. Therefore, in this master thesis we systematically investigated the influence of their addition in the measurement of anti-Xa.
In the master's thesis, we compared five different methods that differ in their antithrombin and dextran sulphate content: four methods from the same manufacturer and one comparable method from a different manufacturer. The methods were tested on samples to which different concentrations of low-molecular-weight heparin and different antithrombin activities had been added in vitro.
The results of the statistical analysis show that the methods differ from each other despite a significant correlation. A significant difference was found between the groups of methods with and without added antithrombin, with the methods with added antithrombin measuring significantly higher anti-Xa values than the methods without antithrombin. This confirms that the measured anti-Xa values are dependent on exogenous antithrombin. A significant variation among methods was observed within the range of endogenous antithrombin activity between 68 and 81 %. Therefore, the choice of method is likely to have a greater influence in individuals with antithrombin activity below and within this range. This theory should be confirmed in patient samples. The method groups with and without the addition of dextran sulphate did not differ significantly from each other, suggesting that the measured anti-Xa values are not dependent on this or that the influence of dextran sulphate is significantly less than the influence of antithrombin.
|
