Bleeding time

Bleeding time is a medical test done on someone to assess their platelet function

The term "template bleeding time" is used when the test is performed to standardized parameters.^[1] This makes it easier to compare data collected at different facilities.

Process

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 standardized 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 (i.e. the time it takes for a platelet plug to form) is measured. Cessation of bleeding can be determined by blotting away the blood every several seconds until the site looks 'glassy'.

Ivy method

The Ivy method is the traditional format for this test. While both the Ivy and the Duke method require the use of a sphygmomanometer, or blood pressure cuff, the Ivy method is more invasive than the Duke method, utilizing an incision on the ventral side of the forearm, whereas the Duke method involves puncture with a lancet or special needle. In the Ivy method, the blood pressure cuff is placed on the upper arm and inflated to 40 mmHg. A lancet or scalpel blade is used to make a shallow incision that is 1 millimeter deep on the underside of the forearm.

A standard-sized incision is made around 10 mm long and 1 mm deep. The time from when the incision 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.

A normal value is less than 9 and a half minutes.^[2]

A prolonged bleeding time may be a result from decreased number of thrombocytes or impaired blood vessels. However, it should also be noted that the depth of the puncture or incision may be the source of error.

Normal values fall between 2 – 9 minutes depending on the method used.

Duke Method

With the Duke method, the patient is pricked with a special needle or lancet, preferably on the earlobe^[3] or fingertip, after having been swabbed with alcohol. The prick is about 3–4 mm deep. The patient then wipes the blood every 30 seconds with a filter paper. The test ceases when bleeding ceases. The usual time is about 1–3 minutes.

Interpretation

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 thrombocytopenia, disseminated intravascular coagulation (DIC), Bernard-Soulier disease, and Glanzmann's thrombasthenia.

Aspirin and other cyclooxygenase inhibitors can prolong bleeding time significantly. While warfarin and heparin have their major effects on coagulation factors, an increased bleeding time is sometimes seen with use of these medications as well.

People with von Willebrand disease usually experience increased bleeding time, as von Willebrand factor is a platelet agglutination protein, but this is not considered an effective diagnostic test for this condition.

It is also prolonged in hypofibrinogenemia.^[4]

Controversy

Many experts regard the bleeding time as useless, in that it does not predict surgical bleeding. Articles supporting this view are often presented by pathologists. Despite such articles (e.g., Peterson et al: The Postoperative Bleeding time Lacks Clinical Benefit; Arch Surg. 1998;133:134-139), the bleeding time continues to be used by many clinicians, primarily surgeons.

References

External links

• MedlinePlus Medical Encyclopedia