Early Awareness Key to Successful Management of Heparin-Induced Thrombocytopenia (HIT)

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Laboratory Tests Confirm Diagnosis

Although HIT is typically diagnosed on the basis of clinical signs, the diagnosis should be confirmed by laboratory testing whenever possible.[4] Laboratory confirmation of HIT serves to justify continued anticoagulant treatment and guide the need for radiological investigation. Functional or antigen assays may be used to detect antibodies to heparin, but to date no laboratory test has the ideal mix of features.

The platelet 14Cserotonin-release assay is the most sensitive and specific test for diagnosing HIT, but it is not considered suitable for clinical application.[2]

The platelet aggregation test is the most widely used of the diagnostic tests for HIT.[2] When using washed platelets, this test offers >90% sensitivity and specificity.[4] Techniques which further enhance the sensitivity and specificity of the platelet aggregation test have been explored and will promote the clinical application of this assay.

A specific heparin-platelet factor 4 enzyme-linked immunosorbent assay (ELISA) assay has arguably better sensitivity than the platelet aggregation test. The increased sensitivity is because the ELISA assay can detect antibodies to IgM and IgA (which are typically not detected by the functional assays), in addition to themore common IgG antibodies.[2]

Should laboratory testing fail to support clinical findings, it is recommended that testing be repeated with the alternative class of assay, if possible, or on a subsequent day.[2]

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