Heparin-induced thrombocytopenia. A contemporary clinical approach to diagnosis and management

A cohort study investigating compliance with guidelines for platelet count monitoring during heparin thromboprophylaxis

BACKGROUND

Heparin is the most common agent used for prevention of venous thromboembolism. To promote early detection of heparin-induced thrombocytopenia, guidelines recommend episodic platelet count monitoring for specified patient populations. However, physician compliance with these guidelines has never been reported for patients receiving heparin for pharmacologic prophylaxis.

AIM

The aim of this study was to evaluate the frequency of and factors associated with physician failure to monitor patient platelet counts.

RESULTS

We conducted a retrospective cohort study of 2350 admissions of patients aged ≥ 18 years who received ≥ 4 consecutive days of prophylactic heparin. There was nonadherence to monitoring recommendations in 659 (28%) patients. Monitoring was not more likely among patients for whom monitoring was recommended compared with patients for whom no monitoring was recommended (31% vs 27%; adjusted hazard ratio, 0.9; 95% CI, 0.7-1.1). Compared with patients admitted to the general medicine service, monitoring was significantly less common among patients admitted to orthopedic surgery or obstetric-gynecologic services (adjusted hazard ratio, 1.6; 95% CI, 1.1-2.2 and adjusted hazard ratio, 2.4; 95% CI, 1.8-3.2, respectively). A decrease in platelet count (≥ 50%) was detected in 90 (4%) patients, but in only 12 (11%) patients was heparin stopped, and in only 11 (12%) patients were heparin-induced thrombocytopenia antibody levels obtained. Of the 11 patients for whom heparin-induced thrombocytopenia antibody levels were obtained, 6 (0.26% of the patient population) were positive.

CONCLUSION

We found that compliance by physicians with platelet count monitoring recommendations was poor for patients who had received heparin for venous thromboembolism prophylaxis, and platelet count monitoring appeared to be unrelated to American College of Chest Physicians recommendations for routine monitoring. Compliance was particularly poor in orthopedic surgery and obstetric-gynecologic services.

Direct thrombin inhibitors in cardiovascular disease

Limitations of commonly used anticoagulants, unfractionated heparin, low-molecular-weight heparin, and oral vitamin K antagonists have prompted the development of alternative therapies. Direct thrombin inhibitors are a new class of anticoagulants that bind directly to thrombin and inhibit its interaction with substrates. In this Review, we critically examine the evidence from randomized controlled trials for the efficacy and safety of the parenteral direct thrombin inhibitors bivalirudin and argatroban, and the novel oral direct thrombin inhibitor dabigatran etexilate, in cardiovascular and thrombotic disease.

Frequency of heparin/platelet factor 4-dependent platelet antibodies in patients undergoing angioplasty and stenting for cardiovascular disease and their role for on-clopidogrel platelet reactivity

BACKGROUND

The frequency of heparin-induced platelet antibodies (H/PF4 antibodies) following heparin exposure during percutaneous intervention with stent implantation is unknown. These antibodies may activate platelets and therefore contribute to high on-clopidogrel residual platelet reactivity (HRPR).

METHODS

We screened 288 patients after angioplasty and stenting for H/PF4 antibodies by an IgG/A/M ELISA. The 44 (15.3%) positive samples were further evaluated for IgG only antibodies, by the particle gel immunoassay (PaGIA), the heparin induced platelet activation assay (HIPA) and MEA. Further, we determined on-treatment platelet reactivity by multiple electrode aggregometry (MEA) in these patients. In vivo platelet activation was assessed by P-selectin expression.

RESULTS

The prevalence of H/PF4 antibodies in the total patients' cohort was 15.3% (95% CI 11.3-20%) by the IgG/A/M ELISA, 9.4% (95% CI 6.3-13.4%) by the IgG ELISA, 11.5% (95% CI 8-15.7%) by PaGIA, 14.2% (95% CI 10.4-18.8%) by MEA, and 2.4% (95% CI 1-4.9%) by HIPA. On-treatment platelet reactivity was similar between patients without and with H/PF4 antibodies [39 AU (6-110 AU) vs. 41 AU (7-91 AU); P = 0.85]. HRPR was seen in 105 patients (37.5%), and occurred to a similar extent in patients without and with H/PF4 antibodies in all test systems (all P > 0.2). Further, there was no difference of the ELISA optical densities using the IgG/A/M or the IgG only ELISA between patients without or with HRPR (all P > 0.3). There was no significant difference of P-selectin expression between patients without or with H/PF4 antibodies (P = 0.97). Noteworthy, none of the patients who developed H/PF4 antibodies had heparin-induced thrombocytopenia or a thromboembolic event.

CONCLUSION

H/PF4 antibodies are not rare in patients undergoing angioplasty and stenting. However, these antibodies are not associated with the occurrence of HRPR.

Thrombosis in suspected heparin-induced thrombocytopenia occurs more often with high antibody levels

OBJECTIVE

The study objective was to determine whether higher antiplatelet factor 4 (PF4)/heparin antibody levels using an enzyme-linked immunosorbent assay are associated with more frequent thrombotic events in patients with clinically suspected heparin-induced thrombocytopenia. Heparin-induced thrombocytopenia is an immune-mediated adverse drug reaction. An enzyme-linked immunosorbent assay detects anti-PF4/heparin antibodies to support a suspected clinical diagnosis of heparin-induced thrombocytopenia. The utility of quantitative enzyme-linked immunosorbent assay results is uncertain.

METHODS

Our single-centered study evaluated quantitative anti-PF4/heparin antibody levels using an enzyme-linked immunosorbent assay in consecutive hospitalized patients with a clinical suspicion of heparin-induced thrombocytopenia and positive anti-PF4/heparin antibody levels between July 2003 and December 2006.

RESULTS

Overall, anti-PF4/heparin antibody values were available for 318 patients with clinically suspected heparin-induced thrombocytopenia. The median level was 0.85 optical density units (range 0.31-4.0). The overall rate of arterial or venous thrombosis was 23.3%. A 1-unit increase in anti-PF4/heparin antibody level was associated with an approximate doubling in the odds of thrombosis by 30 days (odds ratio, 1.9; 95% confidence interval, 1.5-2.6; P=.0001). The proportion of patients with pulmonary embolism increased with higher anti-PF4/heparin antibody levels.

CONCLUSION

Higher levels of anti-PF4/heparin antibody are associated with increased thrombosis risk among patients with clinically suspected heparin-induced thrombocytopenia and might have clinical utility for prediction of true heparin-induced thrombocytopenia and the development of thrombosis.

A case of acute coronary artery occlusion associated with very rapid onset heparin-induced thrombosis without thrombocytopenia

An 81-year-old woman was admitted to our hospital with acute heart failure. A coronary stent was implanted in the left circumflex artery (LCX) on day 3, and elective percutaneous coronary intervention for stenosis in the left anterior descending artery (LAD) was planned for day 10. However, 15 minutes after heparin administration, sudden thrombotic occlusion occurred first in the LAD and then in the LCX. Although anti-platelet factor 4/heparin antibody positivity was detected, there was no significant decrease in platelet counts. This suggests that in the event of unexplained thrombosis, heparin-induced thrombosis should be suspected irrespective of platelet counts and early onset.

Adverse effects of heparin

All the adverse effects of heparins are related to their wide variety of biological activities, with bleeding being the most important safety issue, resulting directly from the potency of heparin as an anticoagulant. However, it is hard to define the bleeding risk, since it depends on numerous parameters including the indication, dosage, method, and duration of heparin application, the clinical study design and definition of bleeding as well as patient characteristics and determinants of bleeding such as type of surgery and co-medication. Nonbleeding complications of heparins are caused by binding of heparin molecules to proteins other than antithrombin and to cells, which is generally more pronounced with unfractionated heparin than with low-molecular-weight heparins. Accordingly, heparin-induced thrombocytopenia, the most severe nonbleeding adverse reaction, occurs about 10 times less with low-molecular-weight heparins than with unfractionated heparin. Frequent and therefore important adverse reactions of heparins are skin lesions resulting from delayed-type hypersensitivity reactions. All the other undesirable effects are discussed as well, but they are mostly clinically irrelevant.

Results of a consensus meeting on the use of argatroban in patients with heparin-induced thrombocytopenia requiring antithrombotic therapy - a European Perspective

Argatroban has been introduced as an alternative parenteral anticoagulant for HIT-patients in several European countries in 2005. In 2009 a panel of experts discussed their clinical experience with argatroban balancing risks and benefits of argatroban treatment in managing the highly procoagulant status of HIT-patients. This article summarizes the main conclusions of this round table discussion. An ongoing issue is the appropriate dosing of argatroban in special patient groups. Therefore, dosing recommendations for different HIT-patient groups (ICU patients; non-ICU patients, paediatric patients, and for patients undergoing renal replacement therapies) are summarized in this consensus statement. Because of the strong correlation between argatroban dosing requirements and scores used to characterize the severity of illness (APACHE; SAPS, SOFA) suitable dosing nomograms are given. This consensus statement contributes to clinically relevant information on the appropriate use and monitoring of argatroban based on the current literature, and provides additional information from clinical experience. As the two other approved drugs for HIT, danaparoid and lepirudin are either currently not available due to manufacturing problems (danaparoid) or will be withdrawn from the market in 2012 (lepirudin), this report should guide physicians who have limited experience with argatroban how to use this drug safely in patients with HIT.

Bivalirudin dosing adjustments for reduced renal function with or without hemodialysis in the management of heparin-induced thrombocytopenia

BACKGROUND

While not approved by the Food and Drug Administration for treatment of heparin-induced thrombocytopenia (HIT), except in patients undergoing percutaneous interventions, the direct thrombin inhibitor bivalirudin is a treatment option that is gaining use. An initial dose of bivalirudin 0.15-0.2 mg/kg/h, adjusted to an activated partial thromboplastin time (aPTT) of 1.5-2.5 times the baseline value, has been suggested. Initial dosing in patients with renal dysfunction, including those on hemodialysis, is unclear.

OBJECTIVE

To evaluate initial bivalirudin dosing requirements in patients with and without renal dysfunction, including patients on different forms of dialysis.

METHODS

A retrospective analysis of 135 patients treated with bivalirudin for HIT between June 2004 and October 2009 was conducted at a tertiary care medical center. The patients were divided into groups, based on renal function. Patients receiving dialysis were divided into 3 subgroups based on the mode of hemodialysis: intermittent hemodialysis (IHD, n = 24), sustained low-efficiency daily diafiltration (SLEDD, n = 12), or continuous renal replacement therapy (CRRT, n = 5). Patients not receiving dialysis were separated into 3 subgroups based on calculated creatinine clearance (CrCl): CrCl >60 mL/min (n = 52), CrCl 30-60 mL/min (n = 26), and CrCl <30 mL/min (n = 16).

RESULTS

Compared with patients with normal renal function (CrCl >60 mL/min), patients with differing degrees of renal dysfunction (CrCl 30-60 and <30 mL/min) required lower doses of bivalirudin to achieve aPTT goal (0.13 vs 0.08 vs 0.05 mg/kg/h, respectively; p < 0.001). Patients on dialysis (IHD, SLEDD, CRRT) also required dose reductions (0.07, 0.09, and 0.07 mg/kg/h) compared with patients with normal renal function, but higher dosing requirements than patients not receiving dialysis with CrCl <30 mL/min.

CONCLUSIONS

Patients with renal dysfunction require a reduced dose of bivalirudin to reach a therapeutic aPTT goal. Slightly higher doses may be observed in patients receiving hemodialysis.

Thrombocytopenia following percutaneous coronary intervention

BACKGROUND

Thrombocytopenia following percutaneous coronary intervention (PCI) is an underappreciated condition that is often clinically challenging. There are no guidelines on the management of patients with this condition.

OBJECTIVE

To review recent data in etiologies, risk factors, prevention, management, and prognostic implications of thrombocytopenia following PCI.

EVIDENCE ACQUISITION

Search of MEDLINE, EMBASE, the Cochrane Database, and Google Scholar using the term thrombocytopenia + PCI and other relevant keywords to identify systematic reviews, clinical trials, cohort studies, case series, and case reports. The review was limited to English-language articles published between January 1980 and June 2009. Articles on patients with baseline thrombocytopenia prior to PCI were excluded.

EVIDENCE SYNTHESIS

Thrombocytopenia is not infrequent following PCI. The typical patient with post-PCI thrombocytopenia is on multiple therapies that can potentially cause a decrease in the platelet count. Identification of the cause is critical because management of the condition varies significantly based on the etiology. The severity of the thrombocytopenia also determines the clinical management of the patient. Several observational studies have demonstrated the adverse prognostic impact of the complication on clinical outcomes and have identified risk factors.

CONCLUSIONS

Judicious use of therapies that can cause thrombocytopenia, efficient detection of the cause of the decrease in platelet count, and appropriate management of the condition can potentially improve the quality of care and outcomes following PCI. Further research into risk factors that predispose post-PCI patients to developing thrombocytopenia is warranted.

Fondaparinux cross-reacts with heparin antibodies in vitro in a patient with fondaparinux-related thrombocytopenia

Heparin-induced thrombocytopenia (HIT) related to fondaparinux has been rarely reported, although the ability of fondaparinux to cross-react with heparin antibodies has been often a subject of debate. A patient previously exposed to unfractionated heparin and low-molecular-weight heparin (LMWH) was diagnosed with HIT. During treatment with fondaparinux for 5 consecutive days, his thrombocytopenia significantly deteriorated. A functional platelet activation test in vitro showed clear platelet activation after serum exposure with fondaparinux. After discontinuation of fondaparinux, the platelet count was rapidly reestablished. Fondaparinux cross-reacted with heparin antibodies in this case of HIT, resulting in a deterioration of thrombocytopenia. The implication of this drug in HIT was observed clinically and demonstrated in vitro using a platelet activation test.

Successful preemptive renal retransplantation in a patient with previous acute graft loss secondary to HIT type II: a case report and review of literature

Type II heparin-induced thrombocytopenia (HIT II) is an immune-mediated reaction to heparin administration associated with thrombocytopenia and thrombotic complication with potentially serious outcome. We report a case of a 50-year-old man with history of autosomal dominant polycystic kidney disease (ADPKD), homocystinemia, and history of deep vein thrombosis (DVT), who was switched to intravenous heparin from oral coumadin preoperatively in preparation for preemptive living related renal transplant. Following the operation heparin-induced thrombocytopenia type II lead to graft renal artery thrombosis and subsequent graft loss. One year after first transplant patient underwent successful second living unrelated kidney transplantation with no complications with continued anticoagulation with coumadin and with no reexposure to heparin. Two years after the second transplant and 1 year after stopping anticoagulation, patient was readmitted with bilateral lower extremity DVT and high probability of pulmonary embolism. He was given argatroban on admission as a bridge to anticoagulation with lifelong coumadin therapy and is doing well with excellent graft function. To our knowledge, this is the third reported case of HIT in renal transplantation, second reported case associated with graft loss secondary to HIT and the first reported case of successful retransplantation after initial HIT with graft loss. Heparin-induced thrombocytopenia in transplantation can lead to catastrophic consequences in organ recipients. Successful management of this condition emphasizes promptness of diagnosis and treatment and complete cessation of heparin exposure.

Drug-induced thrombocytopenia in critically ill patients

Thrombocytopenia occurs in 15% to 58% of intensive care unit patients. The incidence varies based upon patient population, timing and frequency of platelet monitoring, and definition of thrombocytopenia. Up to 25% of acutely ill patients develop drug-induced thrombocytopenia. When drug-induced thrombocytopenia is suspected, nondrug related causes must be evaluated and excluded. Establishing the diagnosis of drug-induced thrombocytopenia is challenging, as hundreds of medications have been implicated. Medications commonly associated with drug-induced thrombocytopenia include glycoprotein IIb/IIIa inhibitors, cinchona alkaloids, antibiotics, anticonvulsants, and heparin. Once the diagnosis is suspected, clinicians should identify the start date of medications to assess the timeline of development. The likelihood of each medication causing thrombocytopenia must be evaluated. The risk vs. benefit of discontinuing the suspected medication and availability of alternative medications must be assessed. The role of corticosteroids, immune globulin, and plasmapheresis is uncertain. Once the offending agent has been discontinued, the overall prognosis is excellent. In the case of suspected or confirmed heparin-induced thrombocytopenia, an alternative anticoagulant should be initiated. Drug-induced thrombocytopenia should be documented in the medical record and reported according to institutional and national standards. This review focuses on immune-mediated drug-induced thrombocytopenia from medications commonly utilized in the critically ill patient.

Selecting the optimal antithrombotic regimen for patients with acute coronary syndromes undergoing percutaneous coronary intervention

The wide variety of anticoagulant and antiplatelet agents available for clinical use has made choosing the optimal antithrombotic regimen for patients with acute coronary syndromes undergoing percutaneous coronary intervention a complex task. While there is no single best regimen, from a risk-benefit ratio standpoint, particular regimens may be considered optimal for different patients. We review the mechanisms of action for the commonly prescribed antithrombotic medications, summarize pertinent data from randomized trials on their use in acute coronary syndromes, and provide an algorithm (incorporating data from these trials as well as risk assessment instruments) that will help guide the decision-making process.