A platelet blood count is a blood test that measures the average number of platelets in the blood. Platelets help the blood heal wounds and prevent excessive bleeding. High or low platelet levels can be a sign of a severe condition.
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.
The test gives a platelet count per microliter (mcL) of blood.
The measurement is the number of platelets a person has, on average, per microliter.
The ideal platelet range is 150,000 to 400,000 per mcL in most healthy people.
Low platelet count is known as thrombocytopenia. High platelet count is known as thrombocytosis.
The test can be done on its own or as part of a CBC test. A doctor will often perform a platelet count test if they suspect a person has a disorder that affects platelet count.
The test involves drawing blood from a vein in the arm or hand.
Obtaining a sample of blood 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. Most people feel fine after the test, but some experience mild aching pain at the site of the needle stick for 1 to 2 days.
A technician puts the blood sample into a machine that counts the number of platelets and produces a report of the findings.
Is it safe?
The test is very safe, and complications are rare. People with bleeding disorders should tell their doctor about any history of bleeding issues. Most people find that the test is only a brief inconvenience and a source of mild discomfort.
When do you get the results?
The amount of time it takes to get the results back varies.
Hospitals administering the test for emergencies or people about to undergo surgery often get the results back almost immediately. It can take a few days to get the results when a doctor’s office orders the test at an outside lab.
A high platelet count can happen 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.
Higher risk of blood clots
A person’s blood clots more easily 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 who are confined to bed by illness or who cannot move their limbs.
Someone who has an elevated 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.
Less serious and temporary conditions
Some temporary conditions can cause a higher than normal platelet count. A doctor may order a retest a few days or weeks later when this happens. Some common reasons that platelets are temporarily elevated 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
More serious and chronic conditions
If a person’s platelet count remains high, the following medical conditions may be responsible:
- Cancer: Lung, stomach, breast, and ovarian cancers, as well as lymphoma, can cause high platelet counts. Additional blood testing, imaging scans, or a biopsy can test for cancer.
- Anemia: People with iron-deficiency or hemolytic anemia may have high platelets. Further blood testing can detect most forms of anemia.
- Inflammatory disorders: Diseases that cause an inflammatory immune response, such as rheumatoid arthritis or inflammatory bowel disease (IBD), can increase platelet count. A person will have other symptoms in most cases.
- Infections: Some infections, such as tuberculosis, can cause high platelets.
- Splenectomy: Removal of the spleen can cause a temporary increase in platelets.
A low platelet count can make it difficult for the blood to clot, putting a person at risk of excessive bleeding. The cause may be due to an inherited tendency to not produce enough platelets, but the cause may also be unknown. In other cases, it is due to an underlying medical condition.
Higher risk of spontaneous bleeding
If the blood platelet count falls below 20,000 per mcL, a person can begin bleeding spontaneously. People who experience spontaneous bleeding may require a blood transfusion. Low platelet count increases the risk of death in people who have recently experienced a traumatic injury.
Common causes of low platelet volume include:
- Viruses: Viruses, such as mononucleosis, HIV, AIDS, measles, and hepatitis may deplete platelets.
- Medication: Drugs, such as aspirin, H2-blockers, quinidine, antibiotics containing sulfa, and some diuretics may lower platelet count.
- Cancer: Cancer that has spread to the bone marrow can harm the body’s ability to make new platelets. Lymphoma and leukemia are common culprits.
- Anemia: A type of anemia called aplastic anemia reduces the number of all kinds of blood cells, including platelets.
- Infection: A bacterial infection, especially the blood infection sepsis, can reduce platelet count.
- Autoimmune disorders: Autoimmune diseases such as lupus and Crohn’s disease lower platelet count by causing the body to attack its tissue.
- Chemotherapy: Chemotherapy harms existing tissue in addition to cancer cells, which can make it difficult for the body to produce platelets.
- Poisoning: Exposure to some pesticides can damage platelets.
- Cirrhosis: Liver cirrhosis, often due to excessive drinking, can reduce platelet count.
- Chronic bleeding: Any disorder that causes ongoing uncontrolled bleeding, such as stomach ulcers, can deplete platelets.
Platelet count also tends to decline with age. A platelet count that is lower than it once was, or that is on the lower end of normal, may not be a cause for concern in an older adult—especially if there are no other symptoms.
Changes in platelet count may mean that a person has a chronic illness or that there is an issue with the bone marrow.
It is generally not possible, however, to diagnose a medical condition based on platelet count alone. People should talk to 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.