Extreme Thrombocytosis in a Child: Laboratory Approaches and Diagnostic Challenges

Thrombocytosis in children as well as in adult is defined as platelet count ≥ 450 × 10⁹/L, and it is usually a reactive feature to various medical disorders. However, extreme thrombocytosis (platelet count ≥ 1000 × 10⁹/L) is an uncommon finding among pediatric and adult patients, which may indicate more than a reactive phenomenon. We describe a case of a five-year-old boy who was admitted due to recurrent epistaxis. He had no history of allergic tendency or trauma. Physical examination was unremarkable except for shotty neck nodes. Laboratory results at presentation showed normal hemoglobin and total leukocyte count with eosinophilia (0.92 × 10⁹/L), and extreme thrombocytosis. Other relevant investigations including coagulation profile, serum ferritin, liver, and renal function tests were all within normal ranges. Stool samples for ova and cysts were negative. The peripheral blood smear and bone marrow aspirate confirmed thrombocytosis with increased megakaryocytic proliferation and no artefactual reasons for the high platelets such as red blood cell fragments. Different causes of thrombocytosis in childhood were investigated after considering the possible differential diagnoses for extreme thrombocytosis.