Treatment of Heparin-Induced ­Thrombocytopenia: An Overview

Anticoagulants: Therapeutics, Risks, and Toxicity—Special Emphasis on Heparin-Induced Thrombocytopenia (HIT)

Anticoagulants are powerful and unavoidably dangerous drugs that must be carefully selected, monitored, and evaluated. Every patient undergoing treatment is at risk of excess bleeding, since the primary purpose of this class of drugs is to decrease clotting through a variety of biochemical and pharmacological mechanisms. Under the best of circumstances, significant numbers of patients (∼10%) experience toxicity on traditional warfarin oral anticoagulants. Beyond the obvious type A pharmacological toxicity, heparin products carry a seemingly paradoxical/novel risk of increased coagulopathy with limb- and life-threatening thromboembolic injuries (heparin-induced thrombocytopenia [HIT]). As a result of the great toxicity risk, many patients suffer injuries, and litigation is threatened or initiated, frequently against pharmacists and their employers. This article reviews the therapeutic use of old and novel anticoagulants, lists the types of litigation related thereto, and discusses the HIT risk associated with heparin products treatment. Litigation can result from adverse drug reactions and toxicity from anticoagulants.

Heparin-induced thrombocytopenia: towards standardization of platelet factor 4/heparin antigen tests

BACKGROUND

Laboratory confirmation of heparin-induced thrombocytopenia (HIT) is based on detection of heparin-dependent platelet-activating antibodies. Platelet factor 4 (PF4)/heparin enzyme-immunoassays (EIA) are a widely available surrogate for platelet-activating antibodies.

OBJECTIVE

Defining the optical density (OD) reactivity profiles of a PF4/heparin EIA in reference subject and patient populations and the correlation of the EIA results (expressed in OD units) with the prevalence of platelet-activating antibodies.

PATIENTS/METHODS

Using quantile regression we determined the 97.5th percentile of PF4/heparin-immunoglobulin G (IgG) EIA reactivities in non-heparin-treated individuals [blood donors (n = 935)] and patients before heparin therapy (n = 1207). In patients with suspected HIT, we compared the correlation of EIA-IgG reactivities (Greifswald laboratory; n = 2821) and the heparin-induced platelet activation assay (HIPA) with the correlation of reactivities of another EIA-IgG (McMaster laboratory; n = 1956) with the serotonin-release assay (SRA).

RESULTS

PF4/heparin-IgG EIA OD reactivities had a lower OD 97.5th percentile in blood donors compared with patient groups before heparin treatment (P < 0.001). The percentage of sera testing positive in the functional assays strongly correlated with PF4/heparin-IgG EIA OD reactivities in both laboratories with very similar results (correlation coefficient > 0.9) when normalized OD ranges (maximum OD divided by 10) were used instead of absolute OD values.

CONCLUSIONS

Results of PF4/heparin-IgG EIA should not be reported as only positive or negative as there is no single acceptable cut-off value. Instead, reporting PF4/heparin-IgG EIA OD results in ranges allows for risk-stratified prediction for presence of platelet-activating antibodies. Use of normalized OD ranges permits a standardized approach for inter-laboratory comparisons.

Early-onset and persisting thrombocytopenia in post-cardiac surgery patients is rarely due to heparin-induced thrombocytopenia, even when antibody tests are positive

BACKGROUND

The high frequency of thrombocytopenia in post-cardiac surgery patients makes it challenging to diagnose heparin-induced thrombocytopenia (HIT). Two platelet count profiles are reported as indicating possible HIT in these patients: profile 1 describes a platelet count fall that begins between postoperative days 5 and 10, whereas profile 2 denotes early-onset thrombocytopenia that persists beyond day 5.

OBJECTIVES

To examine how these platelet count profiles correlate with antibody status and HIT post-cardiac surgery.

METHODS

We prospectively screened 581 cardiac surgery patients for heparin-dependent antibodies by platelet factor 4 (PF4)-heparin immunoassay and platelet-activation test, and performed daily platelet counts (until day 10) with 30-day follow-up.

RESULTS

All three patients with platelet count profile 1 tested positive for platelet-activating anti-PF4-heparin IgG antibodies [odds ratio (OR) 521.7, 95% confidence interval (CI) 3.9-34,000, P = 0.002], and were judged to have HIT. In contrast, none of 25 patients with early-onset and persisting thrombocytopenia (profile 2) was judged to have HIT, including five patients testing positive for platelet-activating anti-PF4-heparin IgG antibodies. In these patients, the frequency of heparin-dependent antibodies did not differ from that in non-thrombocytopenic controls, either for anti-PF4-heparin IgG (OR 1.7, 95% CI 0.7-4.1, P = 0.31) or for platelet-activating antibodies (OR 1.9, 95% CI 0.6-5.7, P = 0.20). Multivariate analysis revealed that type of cardiac surgery, but not HIT antibody status, predicted early-onset and persisting thrombocytopenia. Together, these findings show that HIT was uncommon in this study population [overall frequency, 3/581 (0.5%), 95% CI 0.1-1.5%].

CONCLUSIONS

Thrombocytopenia that begins between 5 and 10 days post-cardiac surgery is highly predictive for HIT. In contrast, early-onset and persisting thrombocytopenia is usually caused by non-HIT factors with coinciding heparin-dependent antibody seroconversion.

A review of 122 published outcomes of danaparoid anticoagulation for intermittent haemodialysis

One hundred and twenty-two case reports of treatment outcomes of danaparoid use for intermittent haemodialysis (HD) in severely ill patients with heparin intolerance (including 97 HIT patients) have been analysed. HD sessions of 4 - 6 hours were successfully conducted daily to 3 times/week for periods of up to 4 years (median 7 sessions/patient (range 1 - >650). In these patients danaparoid use was relatively safe (4 unprovoked non-fatal major bleeds) and efficacious in protecting the circuit (95% no clotting problem) or patient (6 thromboses: 4 fatal or leading to danaparoid discontinuation). HIT diagnosis was improved if recurrent platelet count reduction with each HD and circuit/AV graft clotting were included. Alternative reasons for and very low nadirs of the platelet count undermined the usefulness of the 4 T pre-test HIT predictability scores, but a positive functional serological test confirmed HIT in most patients. Deaths (15.6%) and thrombosis only occurred in HIT cases. Possible reasons are discussed. Replacing the standard intermittent pre-HD dose regimen with the therapeutic infusion regimen to provide continuous daily systemic antithrombotic protection, should further improve efficacy.

CONCLUSION

Danaparoid appears to be a useful alternative antithrombotic for patients with heparin intolerance and renal failure requiring haemodialysis.

Management of anticoagulation in patients with subacute heparin-induced thrombocytopenia scheduled for heart transplantation

Anticoagulation management of patients with recent heparin-induced thrombocytopenia (HIT) requiring cardiopulmonary bypass (CPB) surgery is a serious challenge, and especially difficult in patients requiring urgent heart transplantation. As nonheparin anticoagulants during CPB bear a high risk of major bleeding, these patients are at risk of being taken off the transplant list. Short-term use of unfractionated heparin (UFH) for CPB, with restriction of UFH to the surgery itself, is safe and effective in patients with a history of HIT who test negative for antiplatelet factor 4 (PF4)/heparin antibodies. We present evidence that it is safe to expand the concept of UFH reexposure to patients with subacute HIT (ie, those patients with recent HIT in whom the platelet count has recovered but in whom anti-PF4/heparin IgG antibodies remain detectable) requiring heart transplantation, if they test negative by a sensitive functional assay using washed platelets. This can be lifesaving in patients with end-stage heart failure.

Treatment and prevention of heparin-induced thrombocytopenia: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter about the recognition, treatment, and prevention of heparin-induced thrombocytopenia (HIT) is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patient values may lead to different choices. Among the key recommendations in this chapter are the following: For patients receiving heparin in whom the clinician considers the risk of HIT to be > 1.0%, we recommend platelet count monitoring over no platelet count monitoring (Grade 1C). For patients who are receiving heparin or have received heparin within the previous 2 weeks, we recommend investigating for a diagnosis of HIT if the platelet count falls by >/= 50%, and/or a thrombotic event occurs, between days 5 and 14 (inclusive) following initiation of heparin, even if the patient is no longer receiving heparin therapy when thrombosis or thrombocytopenia has occurred (Grade 1C). For patients with strongly suspected (or confirmed) HIT, whether or not complicated by thrombosis, we recommend use of an alternative, nonheparin anticoagulant (danaparoid [Grade 1B], lepirudin [Grade 1C], argatroban [Grade 1C], fondaparinux [Grade 2C], or bivalirudin [Grade 2C]) over the further use of unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) therapy or initiation/continuation of vitamin K antagonists (VKAs) [Grade 1B]. The guidelines include specific recommendations for nonheparin anticoagulant dosing that differ from the package inserts. For patients with strongly suspected or confirmed HIT, we recommend against the use of vitamin K antagonist (VKA) [coumarin] therapy until after the platelet count has substantially recovered (usually, to at least 150 x 10(9)/L) over starting VKA therapy at a lower platelet count (Grade 1B); that VKA therapy be started only with low maintenance doses (maximum, 5 mg of warfarin or 6 mg of phenprocoumon) over higher initial doses (Grade 1B); and that the nonheparin anticoagulant (eg, lepirudin, argatroban, danaparoid) be continued until the platelet count has reached a stable plateau, the international normalized ratio (INR) has reached the intended target range, and after a minimum overlap of at least 5 days between nonheparin anticoagulation and VKA therapy rather than a shorter overlap (Grade 1B). For patients receiving VKAs at the time of diagnosis of HIT, we recommend use of vitamin K (10 mg po or 5 to 10 mg IV) [Grade 1C].