Bleeding time is a
medical testdone on someone to assess their plateletfunction.
It involves cutting the underside of the subject's forearm, in an area where there is no hair or visible
veins. The cut is of a standardised width and depth, and is done quickly by an automatic device.
A blood pressure cuff is used above the wound, to maintain venous pressure at a special value. The time it takes for bleeding to stop (as thus the time it takes for a
platelet plugto form) is measured. Cessation of bleeding can be determined by blotting away the blood every several seconds until the site looks 'glassy'.
Bleeding time is affected by platelet function, certain vascular disorders and
von Willebrand Disease--not by other coagulation factors such as haemophilia. Diseases that cause prolonged bleeding time include thrombocytopeniaand disseminated intravascular coagulation(DIC). Aspirinand other cyclooxygenaseinhibitors can prolong bleeding time significantly. While warfarinand heparinhave their major effects on coagulation factors, an increased bleeding time is sometimes seen with use of these medications as well.
von Willebrand diseaseusually experience increased bleeding time, as von Willebrand factoris a platelet agglutination protein, but this is not considered an effective diagnostic test for this condition.
Normal values fall between 2 - 9 minutes depending on the method used.
The Ivy method is the traditional format for this test. In the Ivy method, a blood pressure cuff is placed on the upper arm and inflated to 40 mmHg. A lancet or scalpel blade is used to make a stab wound on the underside of the forearm.
A standard-sized cut is made (usually using an automatic blade.) The time from when the stab wound is made until all bleeding has stopped is measured and is called the bleeding time. Every 30 seconds, filter paper or a paper towel is used to draw off the blood.
The test is finished when bleeding has stopped completely.
[http://www.nlm.nih.gov/medlineplus/ency/article/003656.htm MedlinePlus Medical Encyclopedia]
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