|Values are valid only on day of printing.|
The human platelet factor 4 (H/PF4) antibody immunoassay is an enzyme-linked immunosorbent assays (ELISA) using microwells precoated with an antigen complex of PF4 and polyanionic heparinoid substitute (polyvinyl sulfonate; PVS). Testing is performed on the Biomek FXP liquid handling system using the LIFECODES PF4 Enhanced test kit. Patient serum is incubated in the wells, and binding of antibodies to this complex is detected by binding of a second phosphatase-conjugated antihuman IgG/IgA/IgM antibody. Color is generated when this bound conjugate cleaves a chromogenic phosphate substrate, and is quantitated by light absorption at 405 nm. Results are calculated as the percent of positive standard (reported as reactivity).
Addition of excess heparin (100 U/mL) to patient serum prior to testing will inhibit the reaction between heparin-dependent antibodies and the PF4:PVS complex, and produces a negative result. This procedure is used to confirm that a positive screening result is caused by heparin-dependent antibodies. Results are calculated as the percent heparin inhibition of the reactivity of the antibody.(Collins JL, Aster RH, Moghaddam M, et al: Diagnostic testing for heparin-induced thrombocytopenia [HIT]: An enhanced platelet factor 4 complex enzyme linked immunosorbent assay [PF4 ELISA]. Blood 1997 [Suppl 1] 90:461a; Package insert: LIFECODES PF4 Enhanced assay. Immucor Gen-Probe Incorporated. Waukesha, WI, Rev A 6/2012)
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