Bleeding time

Definition

This is a test that measures the speed at which small blood vessels close off to stop bleeding (the condition of the blood vessels) and platelet function.

How the test is performed

A blood pressure cuff is placed on the upper arm and inflated. Two incisions are made on the lower arm. These are about 10 mm (less than 1/2 inch) long and 1 mm deep (just deep enough to cause minimal bleeding).

The blood pressure cuff is immediately deflated. Blotting paper is touched to the cuts every 30 seconds until the bleeding stops. The length of time it takes for the cuts to stop bleeding is recorded.

How to prepare for the test

Certain medications can interfere with platelet function and therefore may alter test results. Always make sure to tell your doctor what medications you are taking, even over-the-counter preparations.

Your health care provider may ask you to discontinue these medications several days prior to the test. Never discontinue medication without consulting your health care provider.

How the test will feel

The incisions are very shallow and should feel like scratches.

Why the test is performed

This test is useful for detecting bleeding problems.

Normal Values

The bleeding stops within 1 to 9 minutes (what is considered normal varies from lab to lab, depending on how the test is measured).

What abnormal results mean

Prolonged bleeding time may indicate:

• A vascular (blood vessel) defect
• A platelet function defect (see platelet aggregation)
• Thrombocytopenia (low platelets)

Drugs that may increase bleeding times include dextran, indomethacin, and salicylates (including aspirin).

Additional conditions under which the test may be performed:

• Acquired platelet function defect
• Congenital platelet function defects
• Primary thrombocythemia
• Von Willebrand's disease

What the risks are

There is a very slight risk of infection where the skin is broken. Excessive bleeding is rare.

Special considerations

The bleeding time test is used to evaluate the vascular (blood vessel) and platelet factors associated with hemostasis (blood clot formation). When vascular injury occurs, the first hemostatic response is a spastic contraction of the lacerated vessels. Next, platelets adhere to the wall of the vessel at the area of laceration in an attempt to plug the hole. The failure of either process results in a prolonged bleeding time.

Illustrations

Blood clot test

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