Megathrombocytes are large to very large sized blood platelets. Devices used to measure complete blood count parameters do not include these large platelets in the basic count, which can lead to a false diagnosis of thrombopenia (deficiency in circulating platelets). To correct this problem, a search for megathrombocytes under a microscope is added immediately when the platelet count on the device is below normal. The “visual platelet estimate” provided on the report gives a better idea of the total number of platelets for clinical follow-up.
It is normal to find large platelets in response to bleeding. Bone marrow responds by producing young platelets, which are typically larger than old platelets. Certain bone marrow disorders (myeloproliferative syndrome) and some rare genetic diseases (Bernard-Soulier syndrome, May-Hegglin anomaly, etc.) are associated with the abnormal production of very large platelets. Problems with the quality of the blood sample can lead to platelet aggregation (clumping), which will falsely decrease the platelet count provided by the device.