What Is a Clotting Test?

K.C. Bruning

A clotting test is an examination of the coagulating properties of blood. This test is used for several purposes, including diagnosis of suspected medical conditions, observance of a patient taking medication, preparation for surgery, or determining the cause of blood clots. Most tests involve the collection of a blood sample, after which several methods may be used to study the material. A clotting test may also involve making a cut on a particular part of the body in order to determine how long it takes for blood flow to cease.

A clotting test is prescribed to examine blood clot formation.
A clotting test is prescribed to examine blood clot formation.

Laboratory clotting tests can be approached in a variety of ways. In some cases, the blood may simply be examined for platelet count or the number of certain kinds of blood cells, as these can have an effect on clotting. For another type of test, the sample will be treated with an anti-clotting agent and then combined with chemicals that activate clotting so that the timing of the process can be measured. If it takes the blood an abnormally long time to clot under these conditions, then the patient will probably need treatment. There can also be a problem if the blood clots too quickly.

Most clotting tests involve drawing a blood sample.
Most clotting tests involve drawing a blood sample.

The complexity of a laboratory clotting test can vary, depending on what is already known about the blood being studied and the patient’s condition. If a specific condition is suspected, the test can examine particular factors that affect the clotting of blood. When there is less information about the condition, a series of general tests will typically be performed in an attempt to narrow the problem to a specific cause.

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Another kind of clotting test involves making a small cut on the patient and observing the flow of blood. Cuts are usually allowed to bleed for a few minutes. They are typically made in the forearm or earlobe. If a clotting problem appears likely after this test, many doctors will follow up with laboratory tests in order to confirm the diagnosis.

There are several reasons a clotting test may be performed. Patients who are taking warfarin are often tested regularly as the drug thins the blood and can hinder clotting. It can also be administered when a patient bleeds excessively and a clotting problem is suspected or if there is the formation of clots in the veins. Conditions such as liver disease, cancer, bone marrow problems, and uremia may also require blood clot testing. Testing is also a common practice before surgery so that doctors can determine ahead of time whether or not clotting will be an issue for the patient during the procedure.

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