Trending of laboratory variables and affinity purification of the anti-PF4/polyanion antibody. (A) Nadir platelet count (closed circles) and peak serum monoclonal protein (M-protein) levels (open triangles) for each year of clinical data prior to and including the year of presentation to Mayo Clinic are shown on the left and right y-axes, respectively. The lower limit of the normal platelet reference range is depicted by a dotted line (150 × 109/L). (B) HIT, VITT (Ad26.COV2.S-associated), normal control, and patient samples were run in an uncomplexed PF4 (VITT) ELISA. The dotted line represents the positive cutoff of the assay. (C) Experimental scheme for affinity purification of anti-PF4/polyanion antibodies is shown. (D-E) Eluates from PF4/heparin or phosphate-buffered saline (PBS)/control beads were evaluated for their ability to activate PF4-treated platelets (D) and bind PF4/polyanion targets (E). Mean and 1 SD of triplicate measurements are presented in (B), (D), and (E), and (A) presents single measurements of nadir platelet counts and M-protein level. m/z, mass-to-charge ratio; STEMI; ST elevation myocardial infarction; NSTEMI, non-ST elevation myocardial infarction.
