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Bleeding time

 
Medical Encyclopedia: Bleeding Time
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Definition

Bleeding time is a crude test of hemostasis (the arrest or stopping of bleeding). It indicates how well platelets interact with blood vessel walls to form blood clots.

Description

There are four methods to perform the bleeding test. 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 mM Hg. A lancet or scalpel blade is used to make a stab wound on the underside of the forearm. An automatic, spring-loaded blade device is most commonly used to make a standard-sized cut. The area stabbed is selected so that no superficial or visible veins are cut. These veins, because of their size, may have longer bleeding times, especially in people with bleeding defects. 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.

The three other methods of performing the bleeding test are the template, modified template, and Duke methods. The template and modified template methods are variations of the Ivy method. A blood pressure cuff is used and the skin on the forearm prepared as in the Ivy method. A template is placed over the area to be stabbed and two incisions are made in the forearm using the template as a location guide. The main difference between the template and the modified method is the length of the cut made.

For the Duke method, a nick is made in an ear lobe or a fingertip is pricked to cause bleeding. As in the Ivy method, the test is timed from the start of bleeding until bleeding is completely stopped. The disadvantage to the Duke method is that the pressure on the blood veins in the stab area is not constant and the results achieved are less reliable. The advantage to the Duke method is that no scar remains after the test. The other methods may result in a tiny, hairline scar where the wound was made. However, this is largely a cosmetic concern.

— John T. Lohr, PhD


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Sci-Tech Dictionary: bleeding time
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(′blēd·iŋ ′tīm)

(physiology) The time required for bleeding to stop after a small puncture wound.

Dental Dictionary: bleeding time
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n

The time required for blood to stop flowing from a tiny wound. Normal bleeding time is from 2 to 6 minutes. Bleeding time is increased in disorders of platelet count, uremia, and ingestion of aspirin and other antiinflammatory medications.

Wikipedia: Bleeding time
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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.

Contents

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 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 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]

Condition Prothrombin time Partial thromboplastin time Bleeding time
Vitamin K deficiency prolonged prolonged unaffected
Disseminated intravascular coagulation prolonged prolonged prolonged
Haemophilia unaffected prolonged unaffected

References

  1. ^ Template:Cite web .
  2. ^ "Blood Chemistries". http://www.obgyn.ufl.edu/obgyn101/Lab/Blood%20Chemistries.htm. Retrieved 2009-01-02. 
  3. ^ Schafer, Andrew I.; Loscalzo, Joseph (2003). Thrombosis and hemorrhage. Hagerstwon, MD: Lippincott Williams & Wilkins. pp. 397. ISBN 0-7817-3066-X. 
  4. ^ "Bleeding Time". http://www.obgyn.ufl.edu/obgyn101/Lab/Bleeding%20Time.htm. Retrieved 2009-01-02. 

External links

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