What are the factors that can affect the results of the bleeding time?
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Clotting time tests such as prothrombin time (PT) and/or activated partial thromboplastin time (aPTT) are commonly performed in an outpatient or hospital setting to evaluate the hemostatic system for a variety of reasons. Symptoms associated with prolonged clotting times depend on the underlying etiology. Prolonged clotting times of unclear etiology require further evaluation to determine the cause and exclude clinically significant bleeding disorders. Using panel tests with reflex testing to investigate unexpected prolonged clotting times can reduce the number of times blood will need to be drawn to establish a diagnosis and can lead to more rapid diagnosis. It is important to note that anticoagulant medications may affect testing, as can a recent blood transfusion or factor replacement therapy, and appropriate specimen handling is critical to ensure the accuracy of results. Show Indications for TestingIndividuals who have been noted to have a prolonged clotting time (based on results of tests such as PT and/or aPTT) should undergo further evaluation if the cause of the prolonged clotting time is uncertain. Laboratory TestingInitial TestingObtaining a CBC with platelet count may be useful (eg, to help identify or exclude quantitative platelet abnormalities). The following tests, which are available as components of a reflex panel in some laboratories, are appropriate for patients with prolonged PT and/or aPTT but no strong clinical or laboratory evidence of a specific hemostasis disorder:
Observed patterns in the initial test results determine which additional or reflexive testing should be performed; these tests may include coagulation factor assays, Bethesda assays, and/or von Willebrand factor testing. Condition-Specific TestingCondition-specific testing is preferred in cases of a known coagulation disorder or strong clinical suspicion for a particular disorder. In patients with a bleeding presentation, consider testing for factor deficiencies, such as hemophilia A or B or rare factor deficiencies. The patterns of the PT and aPTT results should guide test selection. As shown in the table below, normal PT and aPTT results are seen in some bleeding disorders. In patients with a thrombotic presentation, consider lupus anticoagulant testing. In patients with an asymptomatic presentation, consider lupus anticoagulant testing, testing for factor deficiencies not associated with a bleeding presentation (eg, factor XII, prekallikrein, and high-molecular-weight kininogen [HMWK] deficiencies), and testing for mild factor deficiencies. PT, aPTT, and Platelet Count Results and Associated Causes
Test InterferenceCoagulation tests may be inaccurate in the presence of anticoagulant drugs or other interfering substances. Refer to Impacts of Common Anticoagulants on Coagulation Testing for possible interferences with different coagulation tests based on the specific drug administered. What are the factors that affect bleeding time?Bleeding time is mainly affected by the number and function of platelets, although vasoconstriction or vasodilatation may affect the bleeding time as well.
What are the possible sources of error in doing bleeding time test?Anything that alters platelet function can interfere with the bleeding time. Some examples include aspirin, thrombocytopenia, and uremia. Additional factors include the test procedure and subjective observation by the performing technician. As with all subjective tests, this one is at risk of human error.
What causes decreased bleeding time?The bleeding time can be abnormal when the platelet count is low or the platelets are dysfunctional. Causes of abnormal bleeding time can be hereditary or acquired. Hereditary causes of abnormal bleeding time are as follows: von Willebrand disease.
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