Platelet aggregation test

Definition

The platelet aggregation blood test checks how well platelets, a part of blood, clump together and cause blood to clot.

How the Test is Performed

A blood sample is needed.

The laboratory specialist will look at how the platelets spread out in the liquid part of the blood (plasma) and whether they form clumps after a certain chemical or drug is added. When platelets clump together, the blood sample is clearer. A machine measures the changes in cloudiness and prints a record of the results.

How to Prepare for the Test

Your health care provider may tell you to temporarily stop taking medicines that may affect the test results. Be sure to tell your provider about all the medicines you take. These include:

• Antibiotics
• Antihistamines
• Antidepressants
• Blood thinners, such as aspirin, that make it hard for the blood to clot
• Nonsteroidal anti-inflammatory medicines (NSAIDs)
• Statin drugs for cholesterol

Also, tell your provider about any vitamins or herbal remedies you take.

DO NOT stop taking any medicine without first talking to your provider.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or bruising. This soon goes away.

Why the Test is Performed

Your provider may order this test if you have signs of a bleeding disorder or a low platelet count. It may also be ordered if a member of your family is known to have a bleeding disorder due to platelet dysfunction.

The test can help diagnose problems with platelet function. It may determine whether the problem is due to your genes, another disorder, or a side effect of the medicine.

Normal Results

The normal time it takes for platelets to clump depends on temperature, and may vary from laboratory to laboratory.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

Decreased platelet aggregation may be due to:

• Autoimmune disorders that produce antibodies against platelets
• Fibrin degradation products
• Inherited platelet function defects
• Medicines that block platelet aggregation
• Bone marrow disorders
• Uremia (a result of kidney failure)
• Von Willebrand disease (a bleeding disorder)

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Note: This test is often performed because a person has a bleeding problem. Bleeding may be more of a risk for this person than for people without bleeding problems.

References

Pai M, Moffat KA. Laboratory evaluation of hemostatic and thrombotic disorders. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 127.

Rao AK, Songdej N, Di Paola JA. Platelet disorders and von Willebrand disease. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 41.

Schafer AI. Approach to the patient with bleeding and thrombosis. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 162.