The term "giant platelet" is usually used for platelets which are as large as, or larger, than the red blood cells in the microscopic field (if the MCV is normal). The cell shape may be round and smooth or scalloped and irregular.
Giant platelets may be seen in myeloproliferative and myelodysplastic conditions, autoimmune thrombocytopenia, in association with severe leukemoid reactions, and in inherited conditions such as May-Hegglin anomaly and Bernard-Soulier syndrome. Their presence in the peripheral blood smear should lead to further investigation. The image on the right is a giant platelet that is observed in a case of May-Hegglin anomaly.