Published: 18 Jun 2025

ICD9: 287.1      ICD10: D69.1      ICD11: 3B62.01

"Giant platelets" or "megathrombocytes" are abnormally large platelets in the blood.
Platelets (also called thrombocytes) are small, colorless cell fragments in the blood that help form clots to stop bleeding. A normal platelet is typically 2-4 micrometers in diameter. Megathrombocytes are significantly larger, often exceeding 10 micrometers.

Here's a breakdown of what's important about them:

What they are: Abnormally large blood platelets.

Why they matter: The presence of megathrombocytes can indicate several things, most commonly:

Increased platelet production: The bone marrow, where platelets are made, may be working overtime to produce more platelets. This often happens in response to platelet destruction or consumption in the body. The younger platelets released are larger.

Platelet disorders: Certain genetic or acquired disorders affect platelet formation, leading to the release of abnormally sized platelets.

Possible Causes/Associated Conditions:

Immune Thrombocytopenic Purpura (ITP): An autoimmune disorder where the body attacks its own platelets. The bone marrow tries to compensate by producing more, and these new platelets are often larger.
Thrombotic Thrombocytopenic Purpura (TTP): A rare blood clotting disorder.
Myeloproliferative disorders: Conditions like essential thrombocythemia or myelofibrosis where the bone marrow produces too many platelets.
Bernard-Soulier Syndrome: A rare genetic bleeding disorder where platelets are abnormally large and don't function properly.
May-Hegglin Anomaly: Another rare genetic disorder that causes large platelets and characteristic inclusions in white blood cells.
Post-splenectomy: After the spleen is removed, the number of platelets can increase, and some may be larger.
Recovery from thrombocytopenia: As platelet counts rise after a period of low platelet numbers, larger platelets may be seen.
Certain medications: Some drugs can affect platelet size.
Infections: Some infections can lead to temporary changes in platelet size.
Normal variation: In some cases, a few large platelets may be seen without any underlying medical condition, although this is less common.

How they are detected: Usually found during a complete blood count (CBC) with a peripheral blood smear. The blood smear is examined under a microscope to assess the size and appearance of blood cells, including platelets. An elevated Mean Platelet Volume (MPV) on the CBC can also suggest the presence of megathrombocytes.

What happens next: If megathrombocytes are found, further investigation is usually needed to determine the underlying cause. This may involve:

Reviewing the patient's medical history and medications.
Repeating the CBC and blood smear.
Additional blood tests to look for specific antibodies or genetic markers.
Bone marrow biopsy (in some cases) to examine platelet production.

Important note: The presence of megathrombocytes alone isn't a diagnosis. It's a finding that needs to be interpreted in the context of the patient's overall clinical picture and other lab results.

In summary, giant platelets/megathrombocytes are larger-than-normal platelets that can be an indicator of increased platelet production, platelet disorders, or other underlying medical conditions. Their presence warrants further investigation to determine the cause and guide appropriate management.