Standardization of beta-thromboglobulin and platelet factor 4: a collaborative study to investigate the sources and extent of variation in the measurement of platelet specific proteins.

A collaborative study involving seven laboratories has been carried out to investigate the sources and extent of variation in the measurement by radioimmunoassay of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4). Three plasma samples, one purified beta-TG sample and two purified PF4 samples were assayed against house standards for the respective antigens by each laboratory. The main source of variation of both beta-TG and PF4 measurements was inter-assay (particularly for PF4). It was found that a significant component of this variation was due to the participants' use of different preparations as house standards for beta-TG and for PF4. This indicates that the first step in the standardization of beta-TG and PF4 measurement should be the introduction of a reference for each.