Bleeding Time (BT)

Sample
- This test is done on the patient while he is in the lab.
- No preparation is needed.
Precaution
- This test should be avoided in a patient with a low platelet count.
- There may be false positive (raised value) in a patient with aspirin.
- Avoid in patients with keloid formation or senile skin changes.
- Avoid in patients who have undergone mastectomy or axillary lymph nodes dissection.
- Avoid in uncooperative patients.
- Extreme body temperature gives false results.
- High body temperature prolonged the result.
- Low body temperature lowers the result.
- Avoid and take the history of drugs which may prolong the result like patients on anticoagulant therapy, use of salicylates, antibiotics, streptokinase, nonsteroidal anti-inflammatory drugs, and warfarin.
Indications
- This test is done to evaluate vascular and platelet factors.
- This may be done Preoperatively to rule out the possibility of bleeding e.g. in patients for tonsillectomy etc.
- But this may not be the routine presurgical procedure.
Advantage
- This test is used to differentiate Von Willebrand’s’ disease from mild hemophilia.
Disadvantage
- This test is unable to predict excessive surgical bleeding.
Pathophysiology
- Bleeding time is basically a screening test for:
- Disorders of platelets function:
- The integrity of the vascular wall.
- There are three important compartments of the hemostasis:
- Platelets.
- Blood coagulation factors.
- Vasculature.
- To vascular injury, the first hemostatic response is in the form of contraction of blood vessels.
- The next phase is the adherence of platelets to the injured vessel and plugs the damaged area.
- This phenomenon takes places as follows:
- Vasoconstriction (vasospasm). This is controlled by local, humoral, and neuronal factors.
- Initially, there is vasoconstriction and this is followed by vasodilatation for the influx of the inflammatory cells.
- Formation of platelets plug.
- There are granules discharge from the platelets.
- The platelets aggregates into clumps or plug.
- Then release chemical mediators.
- Platelets are attracted in 15 to 20 seconds to the site of endothelial injury.
- Platelets make plug formation.
- Platelet membrane glycoprotein determines the interaction between the platelets and its external environment.
- The binding of fibrinogen to the platelets leads to platelets aggregation.
- Adherent platelets produce histamine and serotonin will lead to vasoconstriction.
- Vasoconstriction (vasospasm). This is controlled by local, humoral, and neuronal factors.
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- Activation of coagulation factors.
- Formation of a clot.
- Clot retraction.
- Clot dissolution (fibrinolysis).
- Failure of any of the above factors leads to prolonged bleeding.
- If the blood vessels have increased fragility that will also lead to prolonged bleeding time as in old age, in a patient with a defect in the capillaries.
- Blood vessel constriction and platelet adherence are not affected by the coagulation system (Intrinsic and as well as the extrinsic pathway).
- This test is a sensitive measure of platelet functions and the elasticity of blood vessels.
- Normal platelets count is 140,000 to 340,000/cmm.
- Platelets around 20,000/cmm may have a major episode of hemorrhage.
- It is a crude bio-assay but by careful standardization, it has become a reliable and sensitive test of Platelet function.
- Critical values:
- Platelets less than 50,000 may lead to prolonged bleeding time.
- Bleeding time more than 10 minutes has a risk of bleeding and when it is 15 to 20 minutes then bleeding risk may become greater.
NORMAL Values
- Bleeding time normal: 2 to 7 minutes
- Borderline: 7 to 11 minutes.
- Abnormal value: 10 to 15 minutes
- Duke ear lobe method = 1 to 3 minutes
Source 2
- Ivy method = 1 to 9 minutes
- Prolonged bleeding time may be repeated to confirm it. Because if sometimes the large-caliber blood vessel is punctured then bleeding time will be prolonged.
Method for bleeding time:
- IVY method, the most common method where the lancet is used which ensures a precise surgical incision, depth of 1 mm. This will give reproducible results.
- Bleeding Time is determined after superficial skin incision and timing the duration of blood flow from the wounded area until it stops.
- Template method where there is a puncture of the forearm after having pressure in the upper arm 40 mm Hg by blood pressure instrument.
- Clean the volar surface of the forearm.
- Give incision with the template up to 1 mm depth.
- Avoid any visible vein.
- Now blot the blood till it stops.
- Bleeding time is usually normal in coagulation disorders.
longer-than-normal bleeding time may be due to:
- Blood vessel defect.
- Platelet count may be decreased or there is a defect in their function.
- Thrombocytopenia.
- Disseminated intravascular coagulation (D I C) where the platelets are consumed.
- Acute Leukemia.
- Coagulation factor deficiencies like Factor I, II, V, VIII, IX, and XI may show some increase.
- Hodgkin’s disease.
- Severe hepatic disease.
- Hemolytic disease of the newborn.
- Patients with uremia where there are decreases and dysfunction of platelets.
- Patients with anti-inflammatory drugs like aspirin, and indomethacin.
- Severe liver diseases.
- In Von Willebrand disease the bleeding time is variable.
- Critical values = >15 minutes