What Is the Best E&M of Heparin-Induced Thrombocytopenia?

The subsequent length of warfarin therapy is dependent upon the presence or absence of an associated thrombosis. With the presence of a thrombus, the duration should be as defined for other provoked thromboses (three to six months). With no thrombus, the duration should be at least 30 days.

Future anticoagulation in patients with a prior diagnosis of HIT. A history of HIT does not appear to be a risk factor for a higher frequency of forming heparin antibodies upon re-exposure to heparin.⁷ Therefore, in patients with an important indication for heparin (i.e. cardiac or vascular surgery) and a remote history of HIT (>100 days), heparin can be used. In patients with a subacute history of HIT in whom surgery cannot be delayed, heparin products should be avoided and laboratory investigation should be pursued.

If the immunoassay is positive but the functional assay is negative, it is reasonable to use heparin. If both the immunologic and the functional assays are positive, the patient should be considered as having acute HIT, and bivalirudin is recommended.⁴

Back to the Case

Our patient has acute thrombocytopenia with a fall in platelets greater than 50% from baseline. The decrease is within the appropriate time frame for HIT. No thrombosis is found, but no alternate explanation for the thrombocytopenia is apparent. The 4Ts score of 6 indicates high risk for HIT. Heparin was discontinued, and argatroban at a rate of 2 mcg/kg/min was initiated. The immunoassay was positive.

Argatroban was continued until the platelet count reached 150×109/L, at which point warfarin therapy, 5 mg daily, was started. After four days, the INR was 2.2. After another 24 hours, argatroban was discontinued. She was instructed to continue warfarin for another 30 days.

Bottom Line

Evaluation for HIT combines clinical judgment, summarized in the 4Ts, with laboratory evaluation including an immunoassay and possibly a functional assay. Treatment requires immediate discontinuation of heparin, early initiation of a direct thrombin inhibitor, and bridging to warfarin to continue treatment for at least 30 days. TH

Drs. Smith and Rice are members of the Section of Hospital Medicine at Vanderbilt University in Nashville, Tenn.

References

1. Heparin-Induced Thrombocytopenia. MedScape Reference website. Available at: http://emedicine.medscape.com/article/1357846. Accessed Aug. 31, 2010.
2. Heparin-Induced Thrombocytopenia. Orpha.net website. Available at: http://www.orpha.net/data/patho/GB/uk-HIT.pdf. Accessed Aug. 31, 2010.
3. Warkentin TE, Levine MN, Hirsh J, et al. Heparin-induced thrombocytopenia in patients treated with low-molecular-weight heparin or unfractionated heparin. N Engl J Med. 1995;332(20):1330-1335.
4. American Society of Hematology Guidelines: Immune Thrombocytopenia (HIT). American Society of Hematology website. Available at: www.hematology.org/Practice/Guidelines/2934.aspx. Accessed Jan. 28, 2011.
5. Arepally GM, Ortel TL. Heparin-induced thrombocytopenia. Annu Rev Med. 2010;61:77-90.
6. Warkentin TE, Greinacher A, Koster A, Lincoff AM. Treatment and prevention of heparin-induced thrombocytopenia: American College of Chest Physicians Evidence-based Clinical Practice Guidelines (8th Edition). Chest. 2008;133:340S-380S.
7. Warkentin TE. Agents for the treatment of heparin-induced thrombocytopenia. Hematol Oncol Clin N Am. 2010;24:755-775.