What is the role of platelet measurement in the workup of heparin-induced thrombocytopenia (HIT)?

Updated: Sep 10, 2021
  • Author: Sancar Eke, MD, FASN; Chief Editor: Srikanth Nagalla, MD, MS, FACP  more...
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All patients should have baseline platelet counts measured before heparin treatment is started. Guidelines from the American College of Chest Physicians (ACCP) suggest basing further platelet counts on the patient’s risk of HIT. For patients whose risk is considered to be greater than 1% (eg, patients receiving unfractionated heparin after cardiac or orthopedic surgery), the ACCP suggests monitoring the platelet count every 2 or 3 days from days 4-14 of heparin therapy (or until heparin is stopped, whichever comes first). [48]

The ACCP suggests that platelet counts need not be monitored in patients receiving heparin whose risk of HIT is considered to be less than 1%. These include medical patients receiving low molecular weight heparin.

If the platelet count falls by over 50% of the baseline count, even if the nadir remains above 150 x 109/L, and/or a thrombotic event occurs, diagnostic tests should be performed. [48] Diagnostic tests for HIT consist of immunoassays and functional assays.

Immunoassays identify antibodies against heparin/platelet factor 4 (PF4) complexes. Functional assays measure the platelet-activating capacity of PF4/heparin-antibody complexes. Functional assays have greater specificity than immunoassays but are time-consuming and not widely available; many institutions offer only immunoassays.

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