Platelets: What to Know

Medically Reviewed by Jabeen Begum, MD on October 06, 2022
5 min read

Platelets, produced by your bone marrow, are a type of blood cell that prevent blood clots. In this article, we look at platelet structure, functions, conditions affecting platelet count, and whether you can donate platelets.

Platelets are special blood cells tasked with preventing too much blood loss. These small and colorless structures are also known as thrombocytes and resemble cell fragments.

Your body has three types of blood cells — red blood cells, white blood cells, and platelets. Platelets are the smallest of the three and are roughly 20% of the diameter of the blood cells.

Platelets are part of your bloodstream and fuse to prevent blood loss from damaged blood vessels. They are the smallest blood cells and are only visible under a microscope. When they’re dormant, they look like tiny plates, and they're activated once they get signals from damaged blood vessels. They move toward the site of damage and transform into their active form. The platelets have extended tentacles in this form that help them connect with the blood vessels and carry out their repair work.

The main function of the platelets in your body is to prevent blood loss, which is critical for survival. There can be many causes of blood loss. For example, your platelets can come together at the affected area and seal off the wound during an injury. They do this through a process called clotting, which stops the blood flow.

This platelet activity is vital to recovering from surgeries like organ transplants, combating cancer, and overcoming serious injuries.

Platelets are produced in your bone marrow, the spongelike tissue located in the center of your bones. Your body has two types of bone marrow — red and yellow. The red bone marrow produces blood stem cells that later become red blood cells, white blood cells, or platelets. The typical lifespan of platelets after they're produced and released into your bloodstream is around eight to 10 days.

Large cells called megakaryocytes produce platelets in your bone marrow. When megakaryocytes grow larger, they undergo a process of division that breaks them down into several smaller cells, the platelets. It’s estimated that one megakaryocyte gets divided into more than 1,000 platelets. The primary hormone responsible for the production of platelets is thrombopoietin.

As they are fragments of larger cells, platelets are sometimes not considered actual cell bodies, but they contain many structures essential to preventing blood loss. Platelet surfaces have protein molecules that bind to the site of injury and to other platelets to form clusters. Once they attach to the location of injury, specific platelet parts release proteins that plug the damage to the blood vessels. Platelets also contain proteins similar to those found in muscles, giving them the ability to change shape when needed.

The normal platelet count in healthy adults is between 150,000 and 450,000 per microliter of blood. One microliter is equal to one-millionth of a liter.

Individuals with a low platelet count — around 10,000 to 20,000 per microliter — are at increased risk of bleeding. For example, if your platelet count becomes very low, you may lose too much blood after a cut or bruise. Some individuals have an unusually high platelet count. This could range from 500,000 to 1 million platelets per microliter. A low platelet count is called thrombocytopenia, while a high platelet count is known as thrombocytosis. You can learn your platelet count by checking your complete blood count (CBC) test.

While platelets are produced in the bone marrow, they are extensively found in the bloodstream and spleen once released. Your blood is made of plasma, red blood cells, white blood cells, and platelets. Platelets are not only the smallest blood cell but also the lightest. They're usually found in the center of flowing blood in the bloodstream but move out from the center where they meet the blood vessels' surface to prevent blood loss.

Your spleen stores red blood cells and platelets that your body can use during emergencies like massive blood loss. The spleen holds around 25% to 30% of the body’s red blood cells and roughly 25% of all the platelets.

Abnormal platelet counts, whether higher or lower than the normal range, can lead to certain health conditions.

  • Platelet dysfunction. Some serious but rare disorders cause improper platelet function. People with such conditions may have a normal platelet count, but the platelets don’t carry out their regular functions. Platelet dysfunction can be due to factors such as age, genetics, certain medical conditions, race, gender, and medications. Sometimes, existing conditions can cause your immune system to destroy platelets.
  • Primary or essential thrombocytosis. In this condition, your bone marrow produces too many platelets. In some cases, the platelet count can exceed 1 million in number. This may cause blood clots that can stop the blood supply to your heart and brain. Research has yet to identify what causes this.
  • Secondary thrombocytosis. It leads to the same outcome as primary thrombocytosis but is due to existing conditions like anemia, cancer, or infection.
  • Thrombocytopenia. This is when your bone marrow does not produce enough platelets. Certain habits or diseases like alcohol intake, kidney conditions, medicines, cancer, or genes affect your body’s ability to produce platelets. Symptoms of this condition include persistent blood loss from your nose, gums, and digestive tract.

You might wonder if you can donate platelets or if it's safe to do so. According to the American Red Cross, donating platelets is completely safe, with trained medical professionals overseeing the process. Medical staff use fresh, sterile needles for every donation, which they dispose of after a single use. Platelet donation is especially helpful for people who are undergoing cancer treatment.

Cancer treatments like chemotherapy cause damage to the bone marrow, which can affect platelet production. Some cancers like leukemia and lymphoma directly affect the bone marrow, impacting its functions.