Commonly known by its acronym in English (BT), it was introduced as a tool whose function would predict the risk of bleeding after surgery.
It is a test that is no longer widely carried out, at least in the United Kingdom; This is due to the difficulties in standardization and the wide intra- and inter-user variability.
Principles and method
The Ivy method is the traditional method to carry out this test. In the Ivy method, a blood pressure cuff is placed on the upper arm and inflated at 40 mmHg.
Also, in this method, a disposable lancet is used to make two different cuts in the forearm, generally at a distance of 5-10 cm, in rapid succession. Next, a stopwatch starts immediately, and filter paper is used to draw blood every 30 seconds.
The time when the incision is made until all bleeding has stopped is called the bleeding time.
The filter paper should not touch the edge of the clot, as it may alter the platelet plug formation. The test ends when the bleeding has stopped entirely.
An attempt to standardize the method [Template method] involves using an automatic blade that makes a standard size incision [approximately 6 mm long x 1 mm deep] on the volar side of the forearm. Otherwise, the technique is identical.
Historically, measuring bleeding time involved using the ear lobe, the so-called Duke method. However, the ear lobe is highly vascular and is no longer used, at least as extensively as it was years ago, but there are particular cases in which it does, for example, in children.
Scarring can occur at the BT site, and patients should be warned of this. For these reasons, BT is rarely performed in children.
The test depends on an adequate number of functionally active platelets that can adhere to the endothelium to form aggregates. The test is abnormal, that is, prolonged in:
Abnormalities of bleeding time:
- Collagen disorders
- Thrombocytopenia: it is essential to check the platelet count before performing a bleeding time.
A platelet count <50 x 10 / L is considered to prolong BT.
Qualitative platelet disorders
Inherited and acquired platelet disorder that includes antiplatelet drugs such as aspirin and clopidogrel will prolong BT.
However, BT can not reliably predict the risk of perioperative bleeding in patients taking these medications.
Paraproteinemias can also impair platelet function and, therefore, can prolong BT.
Other acquired platelet function disorders will also prolong BT, such as those observed in uremia and myelodysplastic syndromes (MDS) and myeloproliferative disorders (MPD).
Von Willebrand Disease (VWD) A deficiency of von Willebrand Factor (VWF) can prolong BT but not in all cases. BT is no longer recommended as a test for the diagnosis of von Willebrand disease (VWD); see the UKHCDO guidelines on the diagnosis of EVW.
Severe anemia: In patients with anemia, there is a change in the distribution of platelets and a decrease in the interaction of platelets with the vascular endothelium, resulting in prolonged BT. The correction of anemia will improve BT.
Hypophibrinogenemia: Fibrinogen is necessary for the platelet-platelet interaction and, therefore, BT will be prolonged in cases of hypofibrinogenemia.
The reference range for this test is between 2-7 minutes. In cases where the BT exceeds 20 minutes, it is customary to stop in 20 minutes and report the BT as> 20 minutes.
The appropriate investigations, in addition to taking a history of drug exposure, would include:
- Complete blood count that includes the number of platelets and morphology.
- Platelet function test – platelets.
- Measurement of Von Willebrand factor activity.
- Consider a collagen vascular disorder.