n Medical Technology SA - Evaluation and implementation of a semi-automated two-stage factor VIII assay




The quantification of functional Factor VIII (FVIII) levels is used for the diagnosis of patients with Haemophilia A. The most popular method for FVIII quantification is the one-stage FVIII assay. However, there are limitations to this method, for instance the presence of traces of active intermediates may shorten the clotting time and record spuriously high levels of FVIII. Similarly the presence of inhibitors may prolong the clotting time and record spuriously low levels of FVIII. Another disadvantage of the one-stage method is the need for a reagent totally deficient in FVIII. Mutations of the FVIII molecule have also been described that cause falsely elevated results using the one-stage assay. The two-stage method overcomes these limitations. We modified a manual two-stage method to a semi-automated one and evaluated it by testing its reproducibility and sensitivity to low levels of FVIII. This modification made the two-stage method less labour intensive and more time efficient; drawbacks that made the two-stage method unpopular in the past. The semi-automated method is also easier to implement in under-equipped laboratories than automated methods which require expensive automated coagulation instruments. We conclude that the semi-automated method gives reproducible results and is sensitive for low levels of FVIII. We recommend its use in certain circumstances and not to replace the one-stage method as a screening test for Haemophilia A.


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