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Platelet Tests
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Platelet Tests

Platelet tests measure the number and function of platelets in your blood to help diagnose bleeding or clotting disorders.

What are platelet tests?

Platelets, also known as thrombocytes, are small blood cells formed in your bone marrow. They are essential for blood clotting, a process where platelets, proteins, and cells stick together to stop bleeding after an injury. There are two primary types of platelet tests:

Platelet Count Test

This test measures the number of platelets in your blood:

  • Thrombocytopenia: A lower-than-normal platelet count, which can cause excessive bleeding after an injury.
  • Thrombocytosis: A higher-than-normal platelet count, which can lead to dangerous blood clots that block blood flow.

Platelet Function Tests

These tests check the ability of your platelets to form clots. They may include:

  • Closure time: Measures how long it takes for platelets to plug a small hole in a tiny tube.
  • Viscoelastometry: Measures the strength of a blood clot as it forms.
  • Platelet aggregometry: Measures how well platelets clump together (aggregate).
  • Lumiaggregometry: Measures light produced when substances are added to a sample to detect platelet defects.
  • Flow cytometry: Uses lasers to identify proteins on the surface of platelets to diagnose inherited disorders.
  • Bleeding time: A rarely used test that measures how long it takes for bleeding to stop from small cuts on the forearm.

What are they used for?

A platelet count is often part of a complete blood count during a regular checkup. Platelet function tests are used to:

  • Diagnose specific platelet diseases.
  • Check platelet function before complex surgeries or for patients with a history of bleeding disorders.
  • Monitor patients taking blood-thinning medications.

Why do I need a platelet test?

You may need testing if you exhibit symptoms of abnormal platelet levels.

Symptoms of low platelets include:

  • Prolonged bleeding from minor cuts, nosebleeds, or heavy menstrual periods.
  • Unexplained bruising.
  • Petechiae: Pinpoint-sized red spots on the skin.
  • Purpura: Purplish, red, or brown spots caused by bleeding under the skin.
  • Blood in urine or stool.

Symptoms of high platelets include:

  • Headache, dizziness, or weakness.
  • Numbness of hands and feet.
  • Pain, swelling, and warmth in the lower legs.

What happens during a platelet test?

A health care professional will collect a blood sample from a vein in your arm using a small needle. The process typically takes less than five minutes.

What do the results mean?

A lower-than-normal count may indicate cancer (leukemia or lymphoma), viral infections, autoimmune disease, bone marrow damage, cirrhosis, vitamin B12 deficiency, or gestational thrombocytopenia. A higher-than-normal count may be a sign of certain cancers, anemia, inflammatory bowel disease, rheumatoid arthritis, infections, or severe blood loss.

Abnormal function test results may indicate:

  • Inherited disorders: Such as Von Willebrand disease, Glanzmann thrombasthenia, Bernard-Soulier syndrome, or storage pool disease.
  • Acquired disorders: Often caused by kidney failure, leukemia, or myelodysplastic syndrome (MDS).

Frequently Asked Questions

Platelet function tests evaluate how well platelets aggregate and form a clot. Common methods include: - Closure‑time (PFA‑100) – measures the time for a platelet plug to seal a membrane aperture. - Platelet aggregometry – adds agonists (ADP, collagen, epinephrine) to whole blood and records the degree of clumping. - Flow cytometry – tags surface receptors (e.g., GPIb, GPIIb/IIIa) with fluorescent antibodies to detect inherited or acquired defects. These tests help diagnose specific platelet disorders (e.g., Glanzmann thrombasthenia, Bernard‑Soulier syndrome) and assess bleeding risk before surgery or while on antiplatelet drugs.
Yes. Aspirin irreversibly inhibits the cyclooxygenase‑1 pathway, prolonging closure time and reducing aggregation with arachidonic‑acid agonists. Clopidogrel blocks the ADP receptor, similarly impairing ADP‑induced aggregation. For accurate platelet function testing, clinicians usually ask patients to stop these agents for 7‑10 days (aspirin) or 5‑7 days (clopidogrel) before the test, unless stopping would pose a high cardiovascular risk.
If you have a history of unexplained bleeding, are on chronic antiplatelet therapy, have a known platelet disorder, or are undergoing high‑risk procedures (neurosurgery, cardiac surgery, major orthopedic surgery), the surgeon may request a platelet function test. The goal is to confirm adequate clotting ability and decide whether to adjust medications or use peri‑operative platelet transfusions.
platelet count below 150 × 10⁹/L suggests thrombocytopenia, which can result from bone‑marrow problems, immune destruction, certain medications, or infections. Common warning signs include easy bruising, prolonged bleeding from cuts, spontaneous nosebleeds, gum bleeding, or petechiae (tiny red spots) on the skin. If you notice any of these, seek medical evaluation promptly.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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