A platelet count measures the average platelet level in a person’s blood. High or low platelet levels can increase the risk of clotting or excessive bleeding.

Platelets, also called thrombocytes, are fragments of larger cells made in the bone marrow called megakaryocytes. These fragments are crucial to wound healing.

Abnormal platelet levels can lead to various health complications. This article discusses the process of a platelet blood test and what the results mean.

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The mean platelet count blood test is typically part of a complete blood count (CBC) test. A CBC reveals important information about the number of different blood cells in the body.

A platelet count test reveals the average number of platelets a person has per microliter of blood.

Doctors can perform the test independently or as part of a CBC test. They will often perform a platelet count test if they suspect a disorder affecting it.

The test involves drawing blood from a vein in the arm or hand.

Obtaining a blood sample from a vein takes a few minutes and generally causes only minimal discomfort. Occasionally, some people may feel queasy or light-headed while the blood is drawn or shortly after. Taking slow deep breaths is usually enough to calm these feelings. Some people may develop a small mark or bruise.

Typically, doctors will send these samples to a lab for assessment and relay results to the patient in due course.

A person’s platelet levels can change with age, and certain medical conditions can also affect them.

A platelet count that is too low or too high can lead to health complications. A low platelet count is known as thrombocytopenia, while a high platelet count is known as thrombocytosis.

Tests measure average platelet levels per microliter (mcL) of blood. Below are guideline platelet levels.

ResultPlatelet count
high platelet level (thrombocytosis)more than 450,000
normal platelet level150,000–450,000
low platelet level (thrombocytopenia)less than 150,000

A low platelet count can make it difficult for the blood to clot, putting a person at risk of excessive bleeding. Low platelet counts can be due to an inherited medical condition or an acquired medical condition. In some cases, the cause may be unknown.

Risks and complications

If the blood platelet count falls below 20,000 per mcL, a person can begin bleeding spontaneously. This is a medical emergency, and people who experience spontaneous bleeding may require a blood, or platelet, transfusion.

Low platelet count increases the risk of death in people who experience a traumatic injury.

A high platelet count can occur when something causes the bone marrow to make too many platelets. When the reason is unknown, it is called primary or essential thrombocytosis.

When excess platelets are due to an infection or other condition, it is called secondary thrombocytosis.

Risks and complications

A person’s blood clots more quickly when they have too many platelets.

Clotting is a natural protection against bleeding. The body produces more platelets during and following an injury.

However, because platelets cause blood clotting, they can also cause dangerous blood clots in the arms or legs. The blood clot may break off or travel to another area of the body.

The risk of a blood clot is higher in people confined to bed by illness or who cannot move their limbs.

Someone who has a high platelet count because of a recent injury but who must remain in bed may need monitoring to reduce the risk of blood clots as a result.

Several factors can cause a person’s platelet levels to change. These include acute and chronic medical conditions and age.

Causes of high platelet counts

Some temporary conditions can cause a higher-than-normal platelet count. A doctor may order a retest a few days or weeks later if this happens. Some common reasons for high platelet levels include:

  • recovering from a recent injury
  • recovering from blood loss after surgery
  • recovering from excessive drinking or vitamin B12 deficiency
  • intense physical activity or exertion, such as from running a marathon
  • using birth control pills

If a person’s platelet count remains high, chronic medical conditions may be responsible. These may include:

Causes of low platelet counts

Common causes of low platelet volume include:

Platelet count tends to decline with age. A platelet count that is lower than it once was or on the lower end of normal may not be a cause for concern in an older adult — especially if there are no other symptoms.

A person’s platelet levels change with age and can alter due to acute injury, medication changes, and deficiencies.

However, excessively high or low platelet levels can indicate the presence of an underlying health condition, infection, or injury.

It is generally not possible, however, to diagnose a medical condition based on platelet count alone. People should talk with a doctor about further testing if a blood test reveals low platelets.

It is advisable to inform the doctor about any other symptoms, which can help narrow down testing options.

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