For Research Use Only. Not for Use in Diagnostic Procedures. Two-site ELISA method for the measurement of human PF4 (platelet factor 4), on platelet poor human plasma, or any biological sample where PF4 must be measured. Assay designed with affinity purified rabbit polyclonal antibodies for coating the Micro ELISA plate (immunocapture) as well as preparing the Horse Radish Peroxidase (HRP) immunoconjugate marker. This assay measures native or recombinant PF4. It is insensitive to the presence of heparin in the tested sample, and PF4 is measured homogeneously whether its presentation is. The assay calibrator is standardized with the NIBSC International Standard.