Antibody-mediated drug-induced thrombocytopenia: The patient's antibody reacted with normal platelets in the presence of acetaminophen glucuronide, but not with acetaminophen or acetaminophen sulfate

Washed platelets (5 x 10⁶) were combined with patient serum in the presence or absence of 0.4 mM acetaminophen or the metabolite indicated in a final volume of 50 microL. After incubation for one hour, the platelets were washed in the presence or absence of the indicated drug or metabolite (0.2 mM). Bound human IgG was detected by the addition of FITC goat (Fab')2 anti-human IgG (H+L) (1:200; Jackson Immunoresearch, West Grove, PA). No reaction occurred with normal serum under same conditions. Abscissa indicates mean platelet fluorescence intensity in arbitrary units.