Platelet autoantibodies have an impact on the platelet count in patients

Abstract

Background: 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.

Objectives: 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.

Methods: 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.

Results: 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).

Conclusion: 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.

Keywords: antibody concentration; platelet autoantibodies; platelet glycoproteins; thrombocytopenia.