Monday, August 16, 2010

Bleeding Time (BT)

Bleeding Time (BT)

 

Normal Range

3 – 9.5 minutes

Indications and Interpretations         

·        BT is functional test of primary hemostasis

·        BT is single screening test for platelet functional or structural disorders, acquired (e.g. uremia) or congenital

·        Normal BT without suggestive history usually excludes platelet dysfunction. However, a normal BT does not rule out significant defect; with clinical suspicion platelet aggregation should be performed

·        To work up for coagulation disorders in patients, having history of excess bleeding even with normal platelet count.

·        Normal in all other disorders of coagulation except von Willebrand's disease deficiency and some cases of very low plasma fibrinogen.

·        May be useful to monitor treatment of active hemorrhage in patients with prolonged BT due to uremia, Von Willebrand's disease, congenital platelet function abnormalities or severe anemia.

·        No value in performing BT if platelet count < 100,000/cumm as BT is usually prolonged. Prolonged BT with platelet count > 100, 000/cumm usually indicates impaired platelet function (e.g. due to aspirin) or von Willebrand's disease.   

·        Even with a prolonged BT, blood loss does not exceed that of patients with normal BT. Prolonged BT does not necessarily cause increased bleeding.

·        BT increased out of proportion to platelet count suggests von Willebrand's disease or qualitative platelet defect.

Usually prolonged in 

Thrombocytopenia: Platelet count < 100,00/cumm and usually < 80,000/cumm before BT becomes abnormal and < 40,000/cumm before abnormality becomes pronounced.


Platelet function disorders

Hereditary: Von Willebrand's disease, deficient release of platelet glycoproteins, gray platelet syndrome, hereditary hemorrhagic telangiectasia

Acquired: Drugs (aspirin, non- steroidal anti-inflammatory drugs [ NSAIDs], antimicrobials, anticoagulants, anesthetic, calcium channel blockers, β – blockers, phenothiazine, antidepressants), uremia, fibrin degradation products (e.g. disseminated intravascular coagulation [DIC], liver disease, fibrinolytic therapy, immune thrombocytopenias, myeloproliferative disease, vascular disorders, amyloidosis, viral infections, scurvy.

Usually normal in

Hemophilia, severe hereditary hypoprothrombinemia or hypofibrinogenemia.

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