Fibrinolysis standards: a review of the current status

Biological standards are used to calibrate measurements of components of the fibrinolytic system, either for assigning potency values to therapeutic products, or to determine levels in human plasma as an indicator of thrombotic risk. Traditionally WHO International Standards are calibrated in International Units based on consensus values from collaborative studies. The International Unit is defined by the response activity of a given amount of the standard in a bioassay, independent of the method used. Assay validity is based on the assumption that both standard and test preparation contain the same analyte, and the response in an assay is a true function of this analyte. This principle is reflected in the diversity of source materials used to prepare fibrinolysis standards, which has depended on the contemporary preparations they were employed to measure. With advancing recombinant technology, and improved analytical techniques, a reference system based on reference materials and associated reference methods has been recommended for future fibrinolysis standards. Careful consideration and scientific judgement must however be applied when deciding on an approach to develop a new standard, with decisions based on the suitability of a standard to serve its purpose, and not just to satisfy a metrological ideal.