Thrombocytosis, also known as thrombocythemia, is the term for having too many platelets in the blood. Platelets are tiny blood cells that help blood to clot and heal the walls of blood vessels in the instance of bleeding.

There are two types of thrombocytosis, both of which occur due to the bone marrow making too many platelets. The two types are:

  • Primary thrombocytosis: This occurs due to an abnormality in the precursor bone marrow cells that make platelets. It is a blood and bone marrow disorder.Secondary thrombocytosis: Also called reactive thrombocytosis, this occurs because of an underlying condition. There is no abnormality in these precursor cells, but rather the cells are responding to external signals (i.e., signals generated in situations like inflammation or iron deficiency).

A normal platelet range is 150,000 to 450,000 platelets per microliter of blood. Thrombocytosis is diagnosed when platelet counts are greater than 450,000.

This article covers the symptoms of thrombocytosis.

Frequent Symptoms

Frequent symptoms are not typical, as someone living with thrombocytosis often does not experience any, especially early on in its development. Generally, thrombocytosis is discovered during routine blood work or blood work drawn for another reason.

In some cases, symptoms may be present, though this is uncommon. These symptoms may include:

  • Enlarged spleenBurning in the hands or feet, usually worse when exposed to heatBruising to the skin, usually with no known causeBleeding easily from places like the nose or gums, or seeing blood in the stool

Rare Symptoms

It is possible that having too many platelets can cause abnormal clots to form. These clots could potentially form in any blood vessels of the body.

Other risk factors of blood clot development include:

  • Being more than 60 years oldBeing obeseHaving other conditions such as diabetes or heart disease, and smoking or tobacco useHistory of prior blood clotPresence of certain genetic mutations detectable in the blood (JAK2 mutation)

The symptoms listed below are ones that could be associated with blood clots:

Blood clot in the brain (stroke-like symptoms):

  • ConfusionHeadacheVision changesSeizuresWeakness to one side of the body

Blood clot in the lungs:

  • Chest painShortness of breathDry coughPalpitations

Heart attack:

  • Chest painJaw painShortness of breathPalpitationsDizzinessArm pain

Clots in blood vessels in the abdomen:

  • Severe abdominal painBowel changes such as diarrheaNausea and vomitingBlood in the stool

Blood clot in an extremity:

  • Swelling to one extremity (usually a leg)Warmth to the skin of the affected extremityDiscomfort or cramping in the swollen extremity

Complications/Subgroup Complications

Complications associated with thrombocytosis typically involve potential organ damage caused by a blood clot in that organ.

Thrombocytosis in a pregnant person can cause multiple complications such as miscarriage, delayed fetal growth, or abruption of the placenta.

When to See a Doctor/Go to the Hospital

As elevated platelets are often present without symptoms and found during routine lab work, someone living with thrombocytosis may not be aware of the disorder.

Once diagnosed with thrombocytosis, however, medical evaluation or contact with their healthcare provider should be sought if any symptoms develop that are suggestive of a blood clot.

Summary

Thrombocytosis—having too many platelets in the blood—does not normally have symptoms. However, once diagnosed with thrombocytosis, any symptoms of blood clots should warrant seeking emergency medical help.

A Word From Verywell

If you are living with elevated platelets, it is important to be aware of any symptoms that may develop. Medical evaluation should be sought any time you’re concerned, but especially with any concerns of a blood clot. These often need to be treated quickly.