Platelets

What are platelets?

Platelets, also called thrombocytes, are tiny cell fragments in your blood that help with clotting. Platelets are your body’s natural bandage to stop bleeding if you’re injured.

Just a single drop of your blood contains tens of thousands of platelets. It’s important that you have enough (but not too many) of them. Too few platelets can put you at risk of losing too much blood if you’re injured. Too many platelets may increase your risk of dangerous blood clots. The right number of platelets can prevent blood loss during injury without putting you at risk of harmful clots that can restrict blood flow.

What do platelets do?

Your platelets’ primary function is to stop bleeding if a blood vessel gets damaged. During an injury, platelets cluster together at the site of the wound to act as a plug. They also help seal the blood vessels in a process called clotting (coagulation) to prevent excess blood from leaving your body.

The official process to stop bleeding from a damaged blood vessel is called hemostasis. Here’s a breakdown of how platelets function during hemostasis:

• Adhesion: The platelets that circulate in your blood travel to the break in the blood vessel wall and stick (“adhere”) there.
• Activation: The platelets that stick to the wall go through changes that keep hemostasis going. For example, they release substances that cause the blood vessel to narrow so less blood seeps out. They also release substances to attract more platelets to the wound site. They change shape so that it’s easier for the new platelets to bind together.
• Aggregation: The platelets stick together to form a temporary plug that seals the break in the blood vessel wall.

The action of the platelets triggers a series of events called the “coagulation cascade.” During this process, proteins called clotting factors work together to create a substance called fibrin. The fibrin acts as a powerful mesh that reinforces the platelet plug. Together, these elements form a more stable blood clot that stops the bleeding.

Where are platelets located?

Your platelets are located primarily in your bone marrow, blood and spleen.

• Bone marrow: Platelets form from the largest cells in your bone marrow — white blood cells called megakaryocytes. New platelets bud from the megakaryocytes. This is why platelets are considered cell fragments instead of whole cells.
• Blood: Whole blood consists of plasma (the liquid part), red blood cells, white blood cells and platelets. As platelets are the lightest component of whole blood, they are pushed to the walls of your blood vessels, allowing plasma and blood cells to flow through the center. The location helps platelets reach injured blood vessel walls quickly to stop bleeding.
• Spleen: Your spleen stores about one-third of your platelets. It also filters old or damaged platelets.

How many platelets are in my blood?

Platelets and white blood cells make up 1% of your whole blood, along with plasma (55% total volume) and red blood cells (44% total volume). There’s about 1 platelet for every 20 red blood cells in your body.

At any given time, a healthy person has 150,000 to 450,000 platelets per microliter of blood. Your body is continually making platelets because they only live for about seven to 10 days. It takes about 72 hours (three days) for your body to make new platelets.

What do platelets look like?

Platelets are small, colorless cell fragments. They form in the shape of a plate, which is where they get their name. Proteins on the exterior of your platelet walls are sticky to help them adhere to your blood vessels. When actively clotting, platelets extend filaments (a long thread of cells) that resemble legs on a spider. These legs make contact with the broken blood vessel and other platelets to seal the damage and stop the bleeding.

What are the common conditions and disorders that affect platelets?

Most platelet conditions involve having too few or too many platelets:

• Thrombocytopenia (low platelet count): Conditions that prevent your body from making platelets or that destroy them prematurely can cause low platelets. Low platelets increase your bleeding risk.
• Thrombocytosis (high platelet count): Conditions that cause high platelets involve primary problems with platelet production in your bone marrow or secondary problems, where platelets increase in response to something else.

What are common signs or symptoms of a condition affecting my platelets?

Common signs and symptoms of platelet conditions include:

• Bruising (including purpura and petechiae).
• Frequent nosebleeds (epistaxis) or bleeding gums in your mouth.
• Blood in your poop or pee.
• Internal bleeding.
• Excessive bleeding from small wounds.
• Heavy menstrual bleeding (menorrhagia).
• An enlarged spleen (splenomegaly).
• Muscle and joint pain.
• Tingling in hands/feet (paresthesia).
• Leg swelling (edema).
• Severe headaches, weakness or dizziness.

What tests check the health of my platelets?

Tests that check the health of your platelets include:

• Complete blood count (CBC): This blood test identifies how many blood cells and platelets are circulating throughout your body. A platelet count is the specific part of a CBC that checks how many platelets you have.
• Peripheral blood smear (PBS): During this test, a provider looks at a sample of blood beneath a microscope to check for abnormal blood cells and platelets. Oddly shaped or giant platelets may be signs of a condition.
• Blood clotting tests: A prothrombin time test and a partial thromboplastin time test check for multiple factors related to how your blood clots.
• Bone marrow biopsy: Your healthcare provider removes a sample of your bone marrow to examine the health of your cells where platelets form.
• Genetic tests: These tests can show if you have a genetic mutation (a change) that’s causing issues with how your platelets function.

What are common treatments for platelet-related conditions?

Treatments for platelet conditions include:

• Over-the-counter medications: Taking a low dose of aspirin daily can prevent harmful blood clots if you’re at risk.
• Prescription medications: Some medications slow the production of platelets in your bone marrow. Others treat the condition causing abnormal platelets, like autoimmune diseases or infections.
• Plateletpheresis: This procedure is a type of apheresis that treats high platelets. It uses a machine to filter out some of the excess platelets.
• Platelet transfusions: You may need a special type of blood transfusion that involves receiving blood with high concentrations of platelets if you’re at risk of severe blood loss because of low platelets.
• Surgery to remove your spleen (splenectomy): You may need this surgery if your spleen is trapping too many platelets and causing low counts.

How do I keep my platelets healthy?

It’s important to follow your healthcare provider’s instructions if you have a condition that’s causing problems with your platelets. Even if you don’t have a condition, you can care for your platelets by:

• Limiting your alcohol intake.
• Not smoking.
• Avoiding toxic chemicals.
• Taking care to avoid injury.

You can also help care for others by donating platelets. The process is similar to donating blood, except it involves removing some of your platelets and returning the other blood components back to you. Platelet donations help individuals with chronic illnesses, cancer or serious injuries.

What is platelet-rich plasma?

Platelet-rich plasma assists in healing and/or repairing injuries to your body, including sports injuries, joint sprains, pulled muscles, liver disease and large wounds. Platelet-rich plasma forms after a sample of your blood is withdrawn and placed into a centrifuge machine, which separates your whole blood into layers. Plasma and platelets separate from red and white blood cells. Your healthcare provider will inject the platelet-rich plasma to the site of your injury via a shot.

A note from Cleveland Clinic

Platelets are a vital portion of your blood that help you recover from injury quickly. They’re the tiniest blood component, but the work they do is hard to miss. Paper cuts, scraped knees, forehead gashes — all the injuries that you accumulate throughout your lifetime are just temporary setbacks thanks to your platelets. They keep you bandaged even without a bandage. Take steps to improve the health of your platelets by managing any pre-existing medical conditions and being cautious to avoid injury.