Fondaparinux as a Treatment Option for Heparin-Induced Thrombocytopenia

Stella Papadopoulos, Pharm.D.; Jeremy D. Flynn, Pharm.D.; Daniel A. Lewis, Pharm.D.

Disclosures

Pharmacotherapy. 2007;27(6):921-926. 

In This Article

Diagnosis

Clinical suspicion of HIT warrants laboratory testing for the presence of HIT antibodies.[1,2,9,10] This testing typically consists of either serologic or functional assays. Serologic assays, such as the enzyme-linked immunosorbent assay (ELISA), detect antibodies (IgG, IgA, IgM) that react with heparin-PF4 complexes.[1,2,9,10] The ELISA assay is widely available; its reported sensitivity exceeds 97%, and its specificity ranges from 74–86%.[1,2,9,10] Due to the low specificity, this test may detect antibodies in patients without HIT.[3] Therefore, a positive test should be interpreted with caution. Conversely, negative test results provide a high level of confidence that the patient's thrombocytopenia may be due to another cause.

Functional assays detect platelet activation and antibodies that are capable of binding to and activating receptors on platelets.[3] Examples are the serotonin release assay (SRA) and the platelet aggregation test (PAT). The SRA has a sensitivity of 90–98% and a specificity of 89–100%.[1–3] Unfortunately, this assay is technically demanding and time consuming to perform, as it requires the use of donor platelets.[9,10] The PAT can be performed with citrated or washed platelets, but it is more sensitive when performed with washed platelets as opposed to citrated plasma. Unfortunately, performing a PAT with washed platelets is techni-cally demanding.[1,9,10] The PAT is considered to be less sensitive and specific than the SRA or ELISA. In general, if there is an intermediate-to-high clinical suspicion of HIT, serologic testing (i.e., ELISA) is recommended, as this assay is widely available, easy to perform, and has a reasonable turnaround time.[1,3]

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