Thrombophilia other diagnostic studies
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Asiri Ediriwickrema, M.D., M.H.S. [2]
Overview
There are no additional diagnostic studies associated with the diagnosis of thrombophilia. Diagnosis of an inherited thrombophilia is made with specific laboratory findings for each inherited condition.
Other diagnostic studies
There are no additional diagnostic studies associated with the diagnosis of thrombophilia. Diagnosis of an inherited thrombophilia is made with specific laboratory findings for each inherited condition.
- Key points:
- Test selectively: a full panel costs around £300 and tests taken inappropriately may add little, or misinform patient management. Only check for heritable thrombophilia in patients with unprovoked VTE and a positive family history.
- Differentiate venous and arterial thrombosis: arterial events such as most ischaemic stroke or myocardial infarction are not affected by heritable thrombophilias, whereas inherited and acquired thrombophilias may contribute to venous thrombosis.
- Get the timing right: physiological anticoagulant levels are reduced after acute thrombosis, invalidating test results. If a positive antiphospholipid test is found, it should be repeated 12 weeks later, as the antibody may be transient.
- Avoid interfering drugs: anticoagulants interfere with the tests, which should be performed 2 weeks after cessation of vitamin K antagonists, which invalidate protein C and S and lupus anticoagulant assays and 24 hours after low molecular weight heparins are stopped, as these produce a false positive lupus anticoagulant test.
- Use the correct blood bottle: all samples should be taken in sodium citrate (blue vacutainers), filling to the line to ensure the correct dilution is attained. Local policies for anticardiolipin tests vary and may require a clot-activated sample with (red top vacutainer), or without gel for serum separation (gold top vacutainer).
- Appreciate the limitations: tests will not find abnormalities in all patients with VTE and a strong family history, reflecting the likelihood that some heritable states are yet to be identified, especially in the non-Caucasian population. Therefore, a negative set of investigations does not exclude an inherited prothrombotic tendency and if in doubt, a referral to a thrombosis specialist should be made.
- Step-wise approach related to assays and assay methods for individual risk factors included in thrombophilia investigations (testing conditions)