What Is a Platelet Count (PLT)?

A platelet count (PLT) test measures the platelets in your blood. Platelets, or thrombocytes, are cells that form in the bone marrow. They perform the important function of clotting the blood when a blood vessel wall is damaged and bleeding. A simple blood test can determine if someone has a proper amount of platelets, or if they have too few (thrombocytopenia) or too many (thrombocytosis). 

This article discusses the PLT test and explains what a PLT is in more detail.

What Are Platelets? 

Platelets are made inside the bone marrow, the spongy substance in your bones that produces all types of blood cells, including infection-fighting white blood cells as well as red blood cells.

When a blood vessel wall becomes injured, platelets respond to the injured area. They begin to clump together, or aggregate, to heal the blood vessel wall. The activated platelets also send out a signal to recruit more platelets to assist in the plugging of the blood vessel.

In humans, the platelets have an average lifespan about 10 days.

Purpose of PLT Test

Making sure someone has the proper number of platelets can be very important to know, and a platelet count test may be ordered.

The PLT is the number of platelets present in a microliter of blood:

• Thrombocytopenia: Too few platelets—could potentially lead to problems with easy bleeding or bruising
• Thrombocytosis: Too many platelets—can lead to the development of abnormal clotting when not necessary

A healthcare provider may check a PLT as part of a routine healthcare checkup, or they may order it if they suspect someone has too many or too few platelets. 

How Is PLT Tested?

A PLT test can be ordered alone, but is often done in a larger blood test panel called a complete blood count (CBC), which tests for the numbers and sizes of white blood cells, red blood cells, and platelets.

Both tests are completed by drawing a blood sample from a vein, most likely a vein in the arm. No special preparation is needed for a platelet count, and no fasting is required.

Interpreting Results

The normal range of platelets is 150,000 to 450,000 per microliter of blood. If the result falls within this range, there is no abnormality in the platelet count. Having a number less than normal is called thrombocytopenia, and a level higher than 450,000 is called thrombocytosis.

Follow-Up

If the PLT test demonstrates someone has thrombocytosis or thrombocytopenia, following up with a healthcare provider is important. 

High Platelet Count

Thrombocytosis is when there are more than the normal number of platelets in the blood. There are two types of thrombocytosis: primary and secondary. 

Primary Thrombocytosis

With primary thrombocytosis, the bone marrow is functioning abnormally and making too many platelets. Typically, these platelets may not work properly and can lead to abnormal formation of blood clots, or even bleeding. Having blood clots can lead to the development of severe complications, such as a pulmonary embolism, heart attack, or stroke.

To treat primary thrombocytosis, medications can be given to reduce the number of platelets that are being made by the bone marrow. Examples of these medications include Hydrea (hydroxyurea) and Agrylin (anagrelide). Other medications that may be given include aspirin, which helps to keep the platelets from clumping together abnormally.

Secondary Thrombocytosis

In secondary thrombocytosis, the platelets are elevated as a reaction to something else that is going on. This can include:

• Iron deficiency
• Anemia
• Infection
• Inflammation
• Autoimmune diseases
• Nutritional deficiencies such as folate or vitamin B12
• Removal of the spleen

Secondary thrombocytosis can resolve when the underlying disease or condition is treated. In emergency situations, plateletpheresis (removal of platelets from your blood) may be needed. This will temporarily lower the platelet count until other treatment takes effect.

Low Platelet Count

Thrombocytopenia can be caused by a number of factors. These can include decreased production of platelets in the bone marrow, abnormal destruction of the platelets by the immune system, or the spleen holding onto the platelets.

Reasons for decreased platelet production in the bone marrow include:

• Chemical exposure
• Cancer
• Medications
• Heavy alcohol use
• Viruses
• Chemotherapy

Treatment for thrombocytopenia due to low platelet production in the bone marrow differs based on the cause. For example, treating cancer that is causing thrombocytopenia may bring the platelets back up to normal. Stopping a medication that is causing the low platelets can help bring the level up. 

Sometimes the body’s immune system destroys platelets inappropriately; this is referred to as immune thrombocytopenia. If platelets are mildly decreased, treatment may not be needed. In cases where platelets are too low, medications to suppress the immune system—such as steroids—can be given, or immunoglobulin infusions may be used. 

The spleen is normally an area in which some of the body’s platelets are stored. If the spleen is enlarged, it may hold onto more platelets than normal, causing platelet counts to be low. The spleen will release the platelets if they are needed though, and they generally still function properly.

Sometimes a splenectomy, or surgical removal of the spleen, is required if platelet counts are too low. 

Summary

Platelets in your blood, also called thrombocytes, are cells that play a key role in blood clotting. A platelet count test (PLT) will tell you if you have normal levels. Results also will tell you if the levels are too high (called thrombocytosis) or too low (called thrombocytopenia).

These conditions can occur for a number of reasons, including infection or medication-related changes. Nutrition, such as iron or vitamin B12 deficiencies, also may contribute to a platelet count that is too high.

You may require treatment for a high or low platelet count. Talk to your healthcare provider about any symptoms you may be having along with test results to arrive at the correct diagnosis.