Results of 3 immunoassays for VITT antibody detection. Commercial Immucor IgG/A/M anti-PF4/heparin EIA, and the in-house IgG-specific anti-PF4-EIA and anti-PF4/heparin-EIA results for all VITT-positive patients (n = 43; PF4-SRA, ≥20% ¹⁴C-serotonin release) and VITT-negative patients (n = 113; PF4-SRA, ≤20% ¹⁴C-serotonin release). An OD_405nm ≥ 0.40 is considered positive for anti-PF4 and anti-PF4/heparin antibodies in the Immucor IgG/A/M-EIA, shown as a red dotted line. An OD_405nm ≥ 0.45 is considered positive for anti-PF4 and anti-PF4/heparin antibodies in the in-house IgG specific PF4/heparin-EIA and PF4-EIA, also shown as a red dotted line.