Platelet autoantibodies have an impact on the platelet count in patients

It is widely accepted that autoantibodies directed against platelet glycoproteins (GPs) are a major pathophysiological mechanism in immune thrombocytopenia, but little clinical data are available demonstrating an association between platelet antibodies and platelet counts.

We hypothesized that if platelet antibodies are clinically relevant, the number of targeted GPs and antibody concentration should be associated with the extent of thrombocytopenia.

Platelet antibodies were identified in a direct GP-specific test that detects antibodies against GPIIb/IIIa and GPIb/IX. Using laboratory data from 12 335 thrombocytopenic patients with and without GP-specific platelet antibodies, we conducted a large retrospective cohort study.

We identified 1469 adults with GP-specific platelet antibodies in our database with complete entries. Compared with 10 866 adults without antibodies, patients with antibodies had significantly lower median platelet counts (54 G/L [IQR, 29-89] vs 85 G/L [IQR, 52-123], P < .0001). Patients with antibodies against 2 GPs had significantly lower platelet counts than patients with antibodies against 1 GP (47 G/L [IQR, 26-81] vs 62 G/L [IQR, 32-99], P < .0001 for GPIIb/IIIa and 58 G/L [IQR, 32-99], P = .0004 for GPIb/IX). Increasing antibody levels correlated with decreasing platelet counts for anti-GPIIb/IIIa (R² = .69; rho -0.84) and anti-GPIb/IX (R² = .57; rho -0.6).

The presence of autoantibodies against GPIIb/IIIa or GPIb/IX is associated with lower platelet counts. More GPs targeted by autoantibodies and increasing antibody levels predict lower platelet counts. Platelet antibodies appear to be of clinical relevance.