Frequency of Antibodies Directed against Heparin-Platelet Factor 4 in Patients Exposed to Heparin through Chronic Hemodialysis

Temporality of heparin-induced antibodies: a retrospective study in outpatients undergoing hemodialysis on unfractionated heparin

Background

Heparin-induced antibodies (HIA) are responsible for causing heparin-induced thrombocytopenia and thrombosis. Research has shown that the temporality of heparin-induced antibodies does not follow the classic immunologic response. The immunobiology of HIA generation remains unclear with varying in vitro and in vivo data. Outpatients undergoing hemodialysis (HD) are exposed to heparin chronically. The HIA immune response can therefore be investigated in vivo in this population.

Methods

We examined the time between the start of HD using unfractionated heparin and HIA levels in 212 outpatients during a 6-year period. Antibodies were detected on enzyme-linked immunosorbent assay. HIA levels were analyzed to determine significance of the trend over time. HIA subgroups were also analyzed for correlation with subsequent thrombotic events and platelet count during follow up.

Results

Overall, the HIA response in HD was found to peak early with waning antibody response despite continued exposure to heparin. The peak prevalence of a strong immune response (optical density > 1.000) was early and short lived, while weaker immune response (optical density 0.400–1.000) persisted for the first 6 months then declined. The mean follow-up time per patient was 2.3 ± 1.4 years. Despite circulating HIA, including high titers, no patients developed HIT in this sample. There was no association between HIA and thrombocytopenia. There was increased incidence of thrombosis in patients with strong HIA compared to other groups, but this did not achieve statistical significance.

Conclusions

The data suggest a significant temporal pattern of HIA in outpatients undergoing HD using unfractionated heparin. Positive HIA was not found to be significantly associated with thrombocytopenia or thrombosis risk in these patients. However, while not achieving statistical significance, subsequent thrombotic events occurred most frequently in the strong positive HIA group (optical density > 1.000). Further research into HIA and risk of thrombosis in this population is needed.

Increased Prevalence of Antiheparin Platelet Factor 4 Antibodies in Patients May Be Due to Contaminated Heparin

During the period of November 2007 to January 2008, an increased prevalence of adverse reactions to heparin was noted. These adverse events have been attributed to the presence of purposeful contaminant, oversulfated chondroitin sulfate (OSCS) from April 2007 to May 2008. An analysis of dialysis patients' plasma obtained in 2006 and 2007 consistently had a low (5%) prevalence of AHPF4 antibodies. Blood samples from 78 patients on maintenance hemodialysis, who were potentially exposed to OSCS-contaminated heparin, were analyzed for the presence of all AHPF4 antibodies using a commercially available ELISA kit from GTI. Although there was no change in the platelet count of these patients, 15 of 78 patients (19.2%) studied had an increased prevalence of AHPF4 antibodies. Subtyping of the all platelet factor 4 (PF4) antibodies documented showed a higher prevalence of immunoglobulin G antibodies as compared to their previously determined antibodies. These observations suggest that the OSCS contaminant in the recalled heparin triggers an immunogenic response not seen with OSCS-contaminated free heparin.

Frequency of Anti-Heparin-PF4 Complex Antibodies (HIT Antibodies) in Uremic Patients on Chronic Intermittent Hemodialysis

The aim of this study was to determine the frequency of heparin/platelet factor (PF) 4 complex antibodies in 305 uremic patients treated with chronic intermittent hemodialysis using unfractionated heparin or low-molecular-weight heparin for 3 months. Heparin-induced thrombocytopenia (HIT) antibodies were detected by ELISA in 7 patients (2.3%) who had no history of HIT. Two patients abruptly developed HIT associated with the formation of clots in the extracorporeal circuit after they were found to be carrying HIT antibodies. These patients were suspected to have a similar trigger: an increased dose of recombinant human erythropoietin (rHuEPO). The drug might induce parallel changes in hematocrit (Ht) levels and platelet counts until the onset of HIT. After the onset of HIT, a parallel phenomenon between Ht and platelet counts was not found because of the thrombocytopenia due to HIT. Although HIT onset has been reported during the initial phase of dialysis sessions, there have been few reports on the onset of HIT in uremic patients on dialysis with long-term heparin anticoagulation. In this study, HIT was observed in 2 uremic patients on chronic dialysis with intermittent use of heparin. In some patients on chronic intermittent dialysis carrying HIT antibodies, HIT may occur following rHuEPO treatment. The presence of HIT should be borne in mind in chronic dialysis patients carrying HIT antibodies for 3 months or more.

The clinical diagnosis of heparin-induced thrombocytopenia in patients receiving continuous renal replacement therapy

BACKGROUND

Thrombocytopenia is common in critically ill patients who receive continuous renal replacement therapy. Often, these patients receive heparin therapy and the diagnosis of heparin induced thrombocytopenia (HIT) is considered as a potential etiology. No data regarding the clinical diagnosis of HIT is available for patients receiving continuous renal replacement therapy.

PATIENTS AND METHODS

We performed a retrospective study of 29 consecutive patients who received CRRT in a medical-surgical intensive care unit (ICU) and determined trends in platelet counts following CRRT and the frequency of meeting platelet based clinical criteria for consideration of a HIT diagnosis.

RESULTS

For patient exposures to CRRT concurrent with heparin, 54% met at least one clinical threshold for consideration of the diagnosis of HIT. In 31% of exposures, both a platelet count <100,000/mm3 and a >50% decrease from baseline were seen. In contrast, the majority (73-85%) of patients receiving CRRT had a low pre-test probability of HIT using the "4T's" scoring system. Mean platelet counts while on CRRT concurrent with heparin were significantly lower than when patients received heparin alone (P < 0.02).

CONCLUSIONS

The clinical diagnosis of HIT in ICU patients initiating CRRT is challenging given the decrease in platelet counts seen following CRRT initiation in the majority of patients. A prospective study in this population is needed to optimize patient outcomes.

Heparin-induced thrombocytopenia complicating hemodialysis

Hemodialysis complicated by heparin-induced thrombocytopenia (HIT) is a rare event requiring anticoagulation with direct-thrombin inhibitors. Contaminant calcific uremic arteriolopathy (calciphylaxis) further complicates this situation due to the possibility that warfarin anticoagulation may exacerbate skin necrosis. The authors report a patient with renal failure and calciphylaxis who developed HIT after starting hemodialysis. She was successfully treated with Argatroban.

Association of heparin-dependent antibodies and adverse outcomes in hemodialysis patients: a population-based study

OBJECTIVE

To determine whether some adverse outcomes of hemodialysis could be explained by subclinical heparin-induced thrombocytopenia (HIT).

PATIENTS AND METHODS

Platelet factor 4 (PF4)-heparin antibodies were measured by enzyme-linked immunosorbent assay In a population-based cohort of hemodlalysis patients. Participants were then followed up prospectively for thromboembollc events, cardiovascular events, or death.

RESULTS

Of the 59 hemodialysis patients residing In Olmsted County, Minnesota, 57 (97%) agreed to study participation. The mean +/- SD age of the patients was 64 +/- 17 years (median hemodialysis duration, 23 months), and 27 (47%) were women. The enzyme-linked Immunosorbent assay was positive for PF4-heparin antibodies in 2 patients (3.5%). The PF4-heparin antibody content varied over a 10-fold range and was not associated with the duration of hemodialysis (P = .99). During a median follow-up of 798 days, 16 thrombotic events, 37 cardiovascular events, and 23 deaths (Including 13 cardiovascular deaths) occurred. After adjusting for the Framingham risk score, the all-cause mortality rate was significantly higher for patients with the highest tertile of PF4-heparln antibody content compared with patients in the lower tertilles (hazard ratio, 2.47; P = .03). Furthermore, 8 (73%) of deaths in this tertile were due to cardiovascular causes (hazard ratio, 4.14; P = .02).

CONCLUSIONS

Despite repetitive heparin exposure, the prevalence of HIT In patients undergoing maintenance hemodialysis is no greater than that anticipated for other patient populations. However, to our knowledge, this is the first study to show an association between elevated PF4-heparin antibodies and Increased mortality rates in hemodlalysis patients.

Hypercoagulable states and antithrombotic strategies in recurrent vascular access site thrombosis

Vascular access site thrombosis is a major cause of morbidity in patients receiving hemodialysis. The role of hypercoagulable states in recurrent vascular access site thrombosis remains poorly understood. Data are limited regarding systemic anticoagulation to improve access graft patency, because of concern about hemorrhagic complications. We determined the prevalence of hypercoagulable states and clinical outcome (thrombotic and hemorrhagic) after initiation of antithrombotic therapy in a series of patients with recurrent vascular access site thrombosis. We evaluated 31 patients who had sustained 119 thrombotic events that resulted in vascular access graft failure during the year before evaluation. Sixty-eight percent of patients tested had elevated concentrations of antibody to anticardiolipin or topical bovine thrombin, and 18% of patients tested had heparin-induced antibodies. More than 90% of patients had elevated factor VIII concentration, 62% had elevated fibrinogen concentrations, and 42% had elevated C-reactive protein concentrations. Twenty-nine patients were given antithrombotic therapy: 13 with warfarin sodium, 12 with unfractionated heparin (UFH), and 11 with low molecular weight heparin (LMWH). Seven patients received more than one antithrombotic agent, sequentially. Nineteen patients have had no thrombotic events since beginning antithrombotic therapy (10 with warfarin, 3 with UFH, 6 with LMWH). Mean follow-up was 8.6 months (median, 7 months). Eight patients sustained 10 bleeding complications (5 with warfarin, 3 with UFH, and 2 with LMWH). In conclusion, hypercoagulable states are common in patients with recurrent vascular access site thrombosis. Antithrombotic therapy may increase vascular access graft patency, but is associated with significant risk for hemorrhage. Prospective studies are needed to evaluate the role and safety of antithrombotic agents in improving vascular access graft patency.

Alternative methods of anticoagulation for dialysis-dependent patients with heparin-induced thrombocytopenia

Dialysis patients who are continually exposed to heparin are at risk for heparin-induced thrombocytopenia (HIT). Heparin-induced antibodies have been reported to occur in 0-12% of hemodialysis (HD) patients. The diagnosis or suspicion of HIT in this patient population requires careful confirmation of the diagnosis and substitution of heparin with an alternate anticoagulant for dialysis. Alternate agents such as the direct thrombin inhibitors (hirudin and argatroban) are available, but careful dosing and monitoring of the anticoagulant effect are required. Despite careful dosing, hemorrhagic complications have occurred with these agents. Unfortunately there are limited options for treatment of hemorrhagic complications and no specific antidotes are available for the direct thrombin inhibitors. In this report the currently available alternatives to heparin for dialysis, including dosing and monitoring recommendations, are reviewed.

Frequency of anti-heparin-platelet factor 4 antibodies in hemodialysis patients and correlation with recurrent vascular access thrombosis

Heparin-induced thrombocytopenia (HIT), characterized by the formation of antibodies to a complex of platelet factor 4 (PF4) and heparin, is a well-recognized risk factor for thromboembolic complications. The frequency of antibody development varies among patient populations. Hemodialysis patients have repeated heparin exposure and should be at risk of developing HIT. This might, contribute to the development of vascular access thrombosis. We prospectively evaluated 88 hemodialysis patients for the presence of anti-PF4/heparin antibodies. Eighteen patients (20%) had a prior history of 1 or more prior access thrombosis. One patient (1.14%), without a history of graft thrombosis, tested positive for anti-PF4/heparin antibodies. In our study, the presence of anti-PF4/heparin antibodies was rare and was not increased in patients with a history of vascular access thrombosis.

Platelet count, anti-heparin/platelet factor 4 antibodies and tissue factor pathway inhibitor plasma antigen level in chronic dialysis

We studied 50 chronic dialysis patients with end-stage renal disease. Mean platelet count was within normal limits. An inverse linear correlation was observed between pre-dialysis platelet count and serum creatinine (r=0.304, p=0.038). Dialysis caused a decrease in platelet count (216+/-80x10(9)/L, pre; 198+/-68, post; p=0.0001), and the higher the pre-dialysis platelet count, the greater the decrease (r=0.623, p=0.0001). Post-dialysis triglyceride decreased (1.67+/-1.27 mmol/L, pre; 1.23+/-0.96, post; p=0.0001). Tissue factor pathway inhibitor (TFPI) antigen plasma level was higher in uremic patients than in controls (114+/-42 ng/ml vs. 64+/-12, p=0.0001). TFPI increased 2.3 times following dialysis and such an increase was directly correlated with post-dialysis plasma heparin concentration (r=0.571, p=0.0002) and inversely correlated with post-dialysis triglyceride variation (r=0.407, p=0.005). Six of fifty patients (12%) had anti-heparin/platelet factor 4 antibodies (Hab), 3 IgG, and 3 IgM. Female sex and the use of cuprophane membranes were more frequent among Hab-positive patients (p=0.0001), while a lower percentage of them were on anti-aggregating drugs as compared to Hab-negative patients (p=0.002). Only one Hab-positive patient was slightly thrombocytopenic and none showed bleeding or thrombotic manifestations. Serum albumin and y globulin decreased following dialysis in Hab-positive patients, while the opposite was seen in those Hab-negative (-2.47+/-1.72 g/L, vs. 0.21+/-1.77, p=0.001 and -0.48+/-0.60 g/L vs. 0.64+/-0.97, p=0.007, respectively). In vivo factors other than Hab are involved in the development of heparin-induced thrombocytopenia. Besides a blunted immunological response, increased levels of TFPI, the use of anti-aggregating drugs, and the observed behavior of serum proteins might play a role in this regard.