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Diagnostic Tests: Bleeding Time
Overview
Bleeding time is a traditional test that evaluates the function of platelets, specifically their ability to adhere to damaged endothelium and form the initial platelet plug. It does not measure coagulation factors and should not be used when the platelet count is low, because anyone with thrombocytopenia will automatically have a prolonged bleeding time. Instead, bleeding time is helpful only when platelet number is normal but platelet function is suspected to be abnormal.
How the Test Is Performed
To perform the bleeding time test, a blood pressure cuff is inflated to 40 mmHg to standardize vascular pressure and engorge capillaries. Small standardized cuts are then made in the skin, and the time required for bleeding to stop is measured. A prolonged bleeding time indicates impaired platelet adhesion or aggregation.
When Bleeding Time Is the Correct Answer
Bleeding time is chosen when a patient has abnormal bleeding suggestive of a platelet disorder, but the platelet count is normal. These clinical scenarios involve qualitative platelet dysfunction, not a quantitative deficiency. Classic examples include:
These conditions impair platelet function even though platelet numbers remain normal. Thus, a prolonged bleeding time supports the suspicion of a functional platelet abnormality.
Most Accurate Tests
Although bleeding time can suggest platelet dysfunction, it is not the most accurate test for diagnosing specific disorders. More precise evaluations include:
These tests provide definitive diagnostic information for platelet-type bleeding disorders, particularly von Willebrand disease.
Overview
Bleeding time is a traditional test that evaluates the function of platelets, specifically their ability to adhere to damaged endothelium and form the initial platelet plug. It does not measure coagulation factors and should not be used when the platelet count is low, because anyone with thrombocytopenia will automatically have a prolonged bleeding time. Instead, bleeding time is helpful only when platelet number is normal but platelet function is suspected to be abnormal.
How the Test Is Performed
To perform the bleeding time test, a blood pressure cuff is inflated to 40 mmHg to standardize vascular pressure and engorge capillaries. Small standardized cuts are then made in the skin, and the time required for bleeding to stop is measured. A prolonged bleeding time indicates impaired platelet adhesion or aggregation.
When Bleeding Time Is the Correct Answer
Bleeding time is chosen when a patient has abnormal bleeding suggestive of a platelet disorder, but the platelet count is normal. These clinical scenarios involve qualitative platelet dysfunction, not a quantitative deficiency. Classic examples include:
- Von Willebrand disease
- Uremia-induced platelet dysfunction
These conditions impair platelet function even though platelet numbers remain normal. Thus, a prolonged bleeding time supports the suspicion of a functional platelet abnormality.
Most Accurate Tests
Although bleeding time can suggest platelet dysfunction, it is not the most accurate test for diagnosing specific disorders. More precise evaluations include:
- Von Willebrand factor level
- Ristocetin cofactor assay (tests VWF function)
- In vitro platelet aggregation studies (directly assess platelet function)
These tests provide definitive diagnostic information for platelet-type bleeding disorders, particularly von Willebrand disease.
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