Platelet Tests - Understand the Test & Your Results

What are platelet tests?
Platelets, also known as thrombocytes, are small blood cells. They form in your bone marrow, the sponge-like tissue in your bones. Platelets are essential for blood clotting . A blood clot is a mass of blood that forms when platelets, proteins, and cells in the blood stick together. When you get hurt, your body forms a blood clot to stop the bleeding.
There are two types of platelet tests: a platelet count test and platelet function tests.
A platelet count test measures the number of platelets in your blood:
A lower-than-normal platelet count is called thrombocytopenia. This condition can cause you to bleed too much after a cut or other injury that causes bleeding.
A higher-than-normal platelet count is called thrombocytosis. This can make your blood clot more than you need it to. Blood clots can be dangerous because they can block blood flow.
Platelet function tests check your platelets' ability to form clots. Platelet function tests may include one or more of the following:
Closure time. This test measures the time it takes for platelets in a blood sample to plug a small hole in a tiny tube. It helps screen for different platelet disorders .
Viscoelastometry. This test measures the strength of a blood clot as it forms. A blood clot has to be strong to stop your bleeding.
Platelet aggregometry. This group of tests is used to measure how well platelets clump together (aggregate).
Lumiaggregometry. This test measures the amount of light produced when certain substances are added to a blood sample. It can help show if there are defects in the platelets.
Flow cytometry. This test uses lasers to look for proteins on the surface of platelets. It can help diagnose inherited platelet disorders. This specialized test is only available at certain hospitals and laboratories.
Bleeding time. This test measures how long it takes for bleeding to stop after small cuts are made in your forearm. It was once commonly used to screen for various platelet disorders but is not used much anymore.
Other names: platelet count, PLT, PLT count thrombocyte count, platelet function tests, PFT, platelet function assay, PFA, platelet aggregation studies
What are they used for?
A platelet count is most often used to monitor or diagnose conditions that cause too much bleeding or clotting. A platelet count may be included in a complete blood count , a test that is often done as part of a regular checkup .
Platelet function tests may be used to:
Help diagnose certain platelet diseases.
Check platelet function during complex surgical procedures , such as coronary artery bypass surgery and trauma surgery. These types of procedures have an increased risk of bleeding.
Check patients before surgery if they have a personal or family history of bleeding disorders .
Monitor people who are taking blood thinners . These medicines may be given to reduce clotting in people at risk for heart attack or stroke .
Why do I need a platelet test?
You may need platelet count and/or platelet function testing if you have symptoms of having lower-than-normal or higher-than-normal platelets.
Symptoms of lower-than-normal platelets include:
Bleeding for a long time after a minor cut or injury.
Nosebleeds.
Unexplained bruising .
Pinpoint sized red spots on the skin, known as petechiae.
Purplish, red, or brown spots on your skin, known as purpura. These may be caused by bleeding under the skin.
Menstrual periods that have a heavy flow or last a long time.
Blood in your urine, stool (poop), or from your rectum (where stool passes out of your body).
Symptoms of higher-than-normal platelets include:
Numbness of hands and feet
Headache
Dizziness
Weakness
Pain, swelling, and warmth in your lower legs
You may also need platelet function testing if you are:
Having a complicated surgery
Taking medicines to lower blood clotting
What happens during a platelet test?
Most platelet tests are done on a blood sample.
During the test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don't need any special preparations for a platelet count test.
If you are getting a platelet function test, you may need to stop taking certain medicines, such as aspirin and ibuprofen, before your test. Tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to. They will let you know if there are any special instructions to follow.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
If your results show a lower-than-normal platelet count (thrombocytopenia), it may be a sign of:
A cancer that affects the blood, such as leukemia or lymphoma .
A viral infection , such as mononucleosis , hepatitis , or measles .
An autoimmune disease . This is a type of disease that causes your body to attack its own healthy tissues, which can include platelets.
Infection or damage to your bone marrow .
Cirrhosis .
Vitamin B12 deficiency (not enough).
Gestational thrombocytopenia, a common, but mild, low-platelet condition affecting pregnant people. It is not known to cause any harm to a pregnant person or their developing baby. It usually gets better on its own during pregnancy or after birth.
If your results show a higher-than-normal platelet count (thrombocytosis), it may be a sign of:
Certain types of cancer, such as lung cancer or breast cancer
Anemia
Inflammatory bowel disease, such as Crohn's disease and ulcerative colitis
Rheumatoid arthritis
A viral or bacterial infection
Severe blood loss
If your platelet function test results were not normal, it may be a sign of an inherited or acquired platelet disorder:
Inherited disorders are passed down from your family. These conditions are present at birth, but you may not have symptoms until you are older.
Acquired disorders are not present at birth. They may be caused by other diseases, medicines, or environmental exposure. Sometimes, the cause is unknown.
Inherited platelet disorders include:
Von Willebrand disease , a genetic disorder that reduces the production of platelets or causes the platelets to work less effectively. It can cause excess bleeding.
Glanzmann thrombasthenia , a disorder that affects platelets' ability to clump together.
Bernard-Soulier syndrome , another disorder that affects platelets' ability to clump together.
Storage pool disease, a condition that affects platelets' ability to release substances that help platelets clump together.
Acquired platelet disorders may be due to chronic diseases such as:
Kidney failure
Certain types of leukemia
Myelodysplastic syndrome (MDS), a disease of the bone marrow
Your provider may consider your symptoms, medical history, and the results of other blood tests to understand the results of your platelet tests.
Learn more about laboratory tests, reference ranges, and understanding results .
Is there anything else I need to know about platelet function tests?
Platelet tests are sometimes done along with one or more of the following blood tests:
MPV blood test , which measures the size of your platelets
Partial thromboplastin time (PTT) test , which measures the time it takes for your blood to clot
Prothrombin time and INR test , which measures how many seconds it takes for a clot to form in your blood sample
If you are taking anti-platelet medicine, like aspirin, your results show how well your medicine is working.
References
Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; c2024.Blood Clotting Disorders (Hypercoagulable); [reviewed 2022 Jul 01; cited 2024 Apr 09]; [about 13 screens]. Available from: https://my.clevelandclinic.org/health/diseases/16788-blood-clotting-disorders-hypercoagulable-states
Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; c2024. Blood Tests; [reviewed 2022 Dec 06; cited 2024 Apr 09]; [about 16 screens]. Available from: https://my.clevelandclinic.org/health/diagnostics/24508-blood-tests
Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; c2024. MPV Blood Test; [reviewed 2022 July 19; cited 2024 Apr 09]; [about 8 screens]. Available from: https://my.clevelandclinic.org/health/diagnostics/23572-mpv-blood-test
Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; c2024. Platelet Count; [reviewed 2021 Sept 09; cited 2024 Apr 09]; [about 07 screens]. Available from: https://my.clevelandclinic.org/health/diagnostics/21782-platelet-count
Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2024. Thrombocytopenia: Overview; [cited 2024 Apr 09]; [about 10 screens]. Available from: https://my.clevelandclinic.org/health/diseases/14430-thrombocytopenia
Gernsheimer T, James AH, Stasi R. How I treat thrombocytopenia in pregnancy. Blood. [Internet]. 2013 Jan 3 [cited 2024 Apr 09]; 121(1):38-47. Available from: https://pubmed.ncbi.nlm.nih.gov/23149846
Mangla A, Hamad H. Thrombocytopenia in Pregnancy. [Updated 2022 Nov 30; cited 2024 Apr 09]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK547705/
Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2024. Thrombocytopenia (low platelet count); [cited 2024 Apr 09]; [about 4 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/thrombocytopenia/diagnosis-treatment/drc-20378298
National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; NCI Dictionary of Cancer Terms: Platelet; [cited 2024 Apr 09]; [about 1 screen]. Available from: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/platelet
National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Platelet Disorders: Diagnosis; [updated 2022 Mar 24; cited 2024 Apr 09]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health/platelet-disorders/diagnosis
National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Thrombocytopenia; [updated 2022 Mar 24; cited 2024 Apr 09]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/thrombocytopenia#:~:text=Thrombocytopenia
Nemours KidsHealth [Internet]. Jacksonville (FL): The Nemours Foundation; c1995-2024. Getting a Blood Test; [reviewed 2021 Sep; cited 2024 Apr 09]; [about 4 screens]. Available from: https://kidshealth.org/en/parents/blood-tests.html
NIH National Human Genome Research Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Genetic Disorders; [updated 2018 May 18; cited 2024 Apr 09]; [about 3 screens]. Available from: https://www.genome.gov/For-Patients-and-Families/Genetic-Disorders
Paniccia R, Priora R, Liotta AA, Abbate R. Platelet function tests: a comparative review. Vasc Health Risk Manag [Internet]. 2015 Feb 18 [cited 2024 Apr 09]; 11:133-48. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4340464
Parikh F. Infections and Thrombocytopenia. J Assoc Physicians India. [Internet]. 2016 Feb [cited 2024 Apr 09]; 64(2):11-12. Available from: https://pubmed.ncbi.nlm.nih.gov/27730774/
Pathology Tests Explained [Internet]. Alexandria (Australia): Australasian Association for Clinical Biochemistry and Laboratory Medicine; c2024. Platelet Count; [reviewed 2024 Apr 09; cited 2024 Apr 09]; [about 5 screens]. Available from: https://pathologytestsexplained.org.au/ptests-pro.php?q=Platelet+count
Russeau AP, Vall H, Manna B. Bleeding Time. 2023 Aug 8. [cited 2024 Apr 09] In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. PMID: 30725918.
Testing.com [Internet]. Seattle (WA).: OneCare Media; c2023. Bone Marrow Aspiration and Biopsy; [updated 2021 Jan 28; cited 2024 Apr 09]; [about 9 screens]. Available from: https://www.testing.com/tests/bone-marrow-aspiration-and-biopsy/
Testing.com [Internet]. Seattle (WA).: OneCare Media; c2023. Platelet Count (PLT); [updated 2023 Dec 19; cited 2024 Apr 09]; [about 8 screens]. Available from: https://www.testing.com/tests/platelet-count/
Testing.com [Internet]. Seattle (WA).: OneCare Media; c2023. Platelet Function Tests; [modified 2021 Nov 9; cited 2024 Apr 09]; [about 8 screens]. Available from: https://www.testing.com/tests/platelet-function-tests/
Testing.com [Internet]. Seattle (WA).: OneCare Media; c2023. Prothrombin Time and International Normalized Ratio (PT/INR); [updated 2021 Nov 09; cited 2024 Apr 09]; [about 10 screens]. Available from: https://www.testing.com/tests/prothrombin-time-and-international-normalized-ratio-ptinr/
Testing.com [Internet]. Seattle (WA).: OneCare Media; c2023. PTT Blood Test (Partial Thromboplastin Time); [updated 2021 Nov 09; cited 2024 Apr 09]; [about 12 screens]. Available from: https://www.testing.com/tests/partial-thromboplastin-time-ptt-aptt/