Anti‐platelet antibodies in childhood immune thrombocytopenia: Prevalence and prognostic implications

Background Anti‐platelet antibody testing may be useful for the diagnosis and management of childhood immune thrombocytopenia (ITP). Objectives Here we aimed to assess the prevalence and prognostic significance of anti‐platelet glycoprotein‐specific IgM and IgG antibodies. Methods Children with newly diagnosed ITP were included at diagnosis and randomized to an intravenous immunoglobulins (IVIg) or careful observation group (TIKI trial). In this well‐defined and longitudinally followed cohort (N = 179), anti‐platelet glycoprotein‐specific IgM and IgG antibodies were determined by monoclonal antibody‐immobilization of platelet antigens. Results The dominant circulating anti‐platelet antibody class in childhood ITP was IgM (62% of patients); but IgG antibodies were also found (10%). Children without IgM platelet antibodies were older and more often female. There was weak evidence for an association between IgM anti‐GP IIb/IIIa antibodies and an increased bleeding severity (P = .03). The IgM and IgG anti‐platelet responses partially overlapped, and reactivity was frequently directed against multiple glycoproteins. During 1‐year follow‐up, children with IgM antibodies in the observation group displayed a faster platelet recovery compared to children without, also after adjustment for age and preceding infections (P = 7.1 × 10−5). The small group of patients with detectable IgG anti‐platelet antibodies exhibited an almost complete response to IVIg treatment (N = 12; P = .02), suggesting that IVIg was particularly efficacious in these children. Conclusions Testing for circulating anti‐platelet antibodies may be helpful for the clinical prognostication and the guidance of treatment decisions in newly diagnosed childhood ITP. Our data suggest that the development of even more sensitive tests may further improve the clinical value of antibody testing.