Diagnostic Approach to Heparin-Induced Thrombocytopenia

Clinical Assessment and Initial Management

The American Society of Hematology recommends calculating the 4T score to determine pre-test probability, and if the score is intermediate (4-5) or high (≥6), stop all heparin immediately, order anti-PF4 antibodies, and start therapeutic-dose alternative anticoagulation without waiting for laboratory results 1, 2
For patients with low probability (≤3 points), heparin can be continued and other causes of thrombocytopenia should be investigated 1, 2

The American College of Chest Physicians recommends ordering anti-PF4 antibody testing immediately as the initial laboratory test, which detects antibodies against the heparin-platelet factor 4 complex 1
If anti-PF4 antibodies are positive with intermediate or high 4T score, proceed to functional testing for confirmation, such as the Serotonin Release Assay (SRA) or Heparin-Induced Platelet Activation (HIPA) test 1, 3

The American Society of Hematology recommends starting therapeutic-dose alternative anticoagulation immediately if clinical suspicion is intermediate or high, without waiting for laboratory confirmation 2
Baseline coagulation studies, including aPTT and INR, should be ordered before starting alternative anticoagulation, and platelet counts should be monitored every 2-3 days until recovery 3

Platelet transfusions should only be ordered if there is active life-threatening bleeding or a high-risk invasive procedure, as they may paradoxically worsen thrombosis in HIT 3, 4
All sources of heparin exposure should be stopped, including heparin flushes in IV lines, heparin-coated catheters, and subcutaneous heparin prophylaxis 2, 3