Genotype frequencies. FcγRIIa (A) and FcγRIIIa (B) genotypes in HIT patients and Ab⁺ group according to levels of anti-H/PF4 antibodies measured by ELISA. The 0.5 line indicates the cut-off value for H/PF4 ELISA. The 1.5 line indicates the threshold above which patients developed high levels of anti-H/PF4 antibodies.