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:
Blood thinners, such as aspirin, that make it hard for the blood to clot
Nonsteroidal inflammatory drugs (NSAIDs)
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 and determine whether the problem is due to your genes, another disorder, or a side effect of medicine.
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.
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient 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:
Fainting or feeling lightheaded
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.
Schafer A. Approach to the patient with bleeding and thrombosis. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 174.
Schmaier AH. Laboratory evaluation of hemostatic and thrombotic disorders. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 131.
Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA . Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.