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

Haemodialysis-associated thrombocytopenia: interactions among the immune system, membranes and sterilisation methods

We present a case of a 47-year-old man with severe thrombocytopenia. The differential diagnosis for thrombocytopenia is wide. The assessment includes an evaluation for falsely low platelet counts (pseudothrombocytopenia), immune-mediated platelet destruction, bone marrow dysfunction, or increased consumption and sequestration. After extensive and systematic workup, we found a relationship of his thrombocytopenia with haemodialysis. Although not widely recognised by clinicians, partly due to an incomplete understanding of its pathophysiology, haemodialysis is also a potential cause of thrombocytopenia. His platelet counts completely normalised after the substitution of his haemodialysis membrane. We concluded that our patient had haemodialysis-induced thrombocytopenia, most likely secondary to electron-beam sterilisation.

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.

Investigation of a potential protective mechanism against heparin-induced thrombocytopenia in patients on chronic intermittent hemodialysis

BACKGROUND

Heparin-induced thrombocytopenia (HIT) develops as a result of platelet (PLT) activation by anti-platelet factor 4 (PF4)/heparin complex antibodies. Despite repeated exposure to heparin, patients undergoing chronic intermittent hemodialysis (HD) rarely develop HIT. We investigated the possibility that HD decreases/removes PF4 from PLT surfaces and/or plasma, thereby disfavoring immune complex formation as a mechanism of protection against HIT.

MATERIALS AND METHODS

We enrolled 20 patients undergoing chronic HD at the Penn Presbyterian Medical Center. Blood samples were drawn before, during and after treatment in the presence and absence of heparin. PF4, anti-PF4/heparin antibody, heparin, and P-selectin levels were measured.

RESULTS

No patients demonstrated clinical symptoms of HIT. PLT surface PF4 levels decreased and plasma PF4 levels increased concurrently with the increase in plasma heparin concentration. In the absence of heparin, PLT surface and plasma PF4 levels were unchanged. Anti-PF4/heparin antibodies, which were non-functional by the serotonin release assay, were detectable in 8 patients. PLT surface P-selectin levels did not change during treatment.

CONCLUSIONS

Removal of PLT surface and/or plasma PF4 as a mechanism of protection against HIT in patients undergoing HD is not supported by the results of our study, although the transient decrease in PLT surface PF4 in the presence of large amounts of heparin remains a candidate mechanism. The small sample size, single type of dialyzer membrane, and early sampling time points may have led to the inability to detect changes in PF4 levels. Future studies should explore other potential protective mechanisms.

Prevalence and Clinical Significance of Heparin Induced Antibodies in Chronic Hemodialysis Patients and Cardiac Surgery Patients

Introduction

The prevalence of heparin-induced antibodies (HIA) varies widely among reported series, but is generally higher in cardiac surgery than hemodialysis patients. This study was designed to explore the reasons behind the different prevalence of HIA in these two populations.

Methods

Blood samples from all hemodialysis and cardiac surgery patients in our hospital were examined for HIA. Heparin-induced thrombocytopenia (HIT) was suspected when platelet count was <150,000 in the hemodialysis group, and >50% decline in platelet count in the cardiac surgery group.

Results

79 hemodialysis and 40 cardiac surgery patients were studied. HIA prevalence was significantly higher in cardiac surgery than in hemodialysis patients (65% v 10.1%, respectively, P<0.00001). Conversely, the prevalence of suspected clinical HIT was 37.5% in the hemodialysis and 11.5% in the cardiac surgery group. Prevalence of HIA was higher in patients who were tested during the first 90 days of hemodialysis than in those tested at later times. One-year mortality was 37% in HIA positive and 19% in HIA negative hemodialysis patients.

Conclusions

Prevalence of HIA was significantly lower in hemodialysis as compared with cardiac surgery patients. Our data suggest that the observed difference in HIA prevalence was either population dependent, or due to different timing of heparin administration in the two groups.

Low-density lipoprotein apheresis reduces platelet factor 4 on the surface of platelets: a possible protective mechanism against heparin-induced thrombocytopenia and thrombosis

BACKGROUND

Heparin-induced thrombocytopenia and thrombosis (HITT) is characterized by thrombocytopenia due to the formation of antibodies against heparin : platelet factor 4 (PF4) complexes. Despite the exposure to heparin during treatment and predisposition of patients with atherosclerosis to HITT, HITT in patients undergoing low-density lipoprotein (LDL) apheresis is rare. We investigated the possibility that LDL apheresis decreases PF4 on platelet (PLT) surfaces and/or plasma HITT antibody levels, either of which would disfavor HITT.

STUDY DESIGN AND METHODS

We enrolled 25 patients undergoing LDL apheresis at the Hospital of the University of Pennsylvania. Blood samples were drawn before and after treatment. Plasma samples were drawn proximal and distal to the LA-15 treatment column. PF4, HITT antibodies, heparin levels, and P-selectin were measured.

RESULTS

No patient had clinical symptoms of HITT. The LA-15 column was found to efficiently remove PF4. PF4 levels in peripheral blood plasma did not change significantly after LDL apheresis. However, PLT surface PF4 significantly decreased after treatment. HITT antibodies were found in only two patients and were nonfunctional. PLT surface P-selectin did not change during treatment.

CONCLUSIONS

We have demonstrated that LDL apheresis via dextran sulfate absorption removes plasma PF4 and reduces the amount of PF4 on the surface of circulating PLTs. Reduced surface PF4 may decrease antibody formation and/or recognition by HITT antibodies. These data provide a potential explanation for the near lack of HITT in hypercholesterolemic patients undergoing LDL apheresis. They also suggest the possibility that LDL apheresis using dextran sulfate adsorption may have therapeutic value in the treatment of HITT.

Heparin-induced thrombocytopenia: a renal perspective

Heparin-induced thrombocytopenia (HIT) is a clinicopathologic syndrome in which one or more clinical events, usually thrombocytopenia or thrombosis, are temporally related to heparin administration and caused by HIT antibodies. Rapid and accurate diagnosis is essential given the high incidence of thrombosis at around the time of initial disease recognition. Discontinuation of heparin and initiation of alternative anticoagulants reduces HIT-associated morbidity and mortality. The clinical consequences of HIT in hemodialysis patients remain unclear, with several studies reporting no clinical sequelae and others describing complications such as thrombocytopenia or clotting of the extracorporeal circuit. Frequent clotting of the extracorporeal circuit has also been reported in HIT-antibody-positive patients on continuous veno-venous hemofiltration. Several recent findings are of particular interest to nephrologists. An acute systemic reaction has been described as a presentation of HIT in hemodialysis patients shortly after administration of an unfractionated heparin bolus. This syndrome is important to recognize as it might mimic a dialyzer reaction. More recently, the presence of a positive HIT-antibody test or increasing titers of HIT antibody were associated with increased mortality in hemodialysis patients, raising the question of whether these antibodies have a role in the increased cardiovascular mortality seen in these patients. HIT-antibody production is often transient and small numbers of hemodialysis patients with undetectable antibody levels have been rechallenged with heparin without adverse clinical consequences.

Heparin-Induced Thrombocytopenia in Patients Administered Heparin Solely for Hemodialysis

BACKGROUND

Heparin, universally used in patients on dialysis, is the cause for immune-mediated heparin-induced thrombocytopenia (HIT).

METHODS

From an HIT registry, six patients were identified who received recent heparin solely for dialysis, developed HIT, and were treated with argatroban. Platelets counts, aPTTs, argatroban dosing, and outcomes were assessed.

RESULTS

Before HIT was diagnosed, unfractionated heparin was used in doses of 2,000-12,000 units. The mean platelet count fell from 122 +/- 62 x 10(9)/L to 35 +/- 22 x 10(9)/L, and one patient experienced thrombosis. After HIT was diagnosed, heparin was discontinued, and argatroban therapy (mean dose, 1.7 +/- 0.9 microg/kg/min) was administered for 6.5 +/- 4.5 days (mean aPTT, 66.1 +/- 12.4 s). Patients continued on renal replacement therapy. Platelet counts increased during argatroban therapy. A 37-day composite endpoint of death, amputation, or new thrombosis occurred in four (66.7%) patients: three patients died from causes unrelated to thrombosis, and one patient developed new thrombosis after argatroban was discontinued. One patient experienced a hematocrit drop during treatment without overt bleeding or a need for transfusion.

CONCLUSIONS

HIT can occur in patients administered heparin solely for hemodialysis. When HIT is suspected, heparin should be discontinued and an alternative anticoagulation initiated. Argatroban, which is not renally cleared, supports continued renal replacement therapy in HIT patients.

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.

Spontaneous superior sagittal sinus thrombosis secondary to type II heparin-induced thrombocytopenia presenting as an acute subarachnoid hemorrhage

Cerebral sinus thrombosis is a rare cause of spontaneous subarachnoid hemorrhage. The development of cerebral sinus thrombosis as a complication of heparin-induced thrombocytopenia is even rarer. In this paper, we present a 59-year-old patient admitted to our service with cerebral sinus thrombosis secondary to type II heparin-induced thrombocytopenia. We also review the literature in regard to the incidence, pathophysiology and management of this rare clinicopathological entity.

The prevalence of antibodies to the platelet factor 4 -heparin complex and association with access thrombosis in patients on chronic hemodialysis

INTRODUCTION

Heparin-induced thrombocytopenia is a serious complication that can lead to thrombocytopenia, venous and arterial thrombosis. Patients with this disorder develop antibodies to the platelet factor 4-heparin (PF4-H) complex. Hemodialysis patients are repeatedly exposed to heparin and are at risk for developing PF4-H antibodies. We sought to determine the prevalence of PF4-H antibodies in a large cohort of patients on chronic hemodialysis and to evaluate the relationship between PF4-H antibodies and hemodialysis vascular access thrombosis in a case-control study.

MATERIAL AND METHODS

Pre-dialysis blood samples were drawn on 419 patients; 107 cases with access thrombosis and 312 controls that never had access thrombosis. All samples were screened for PF4-H antibodies using an ELISA assay (GTI PF4 Enhanced, GTI Diagnostics). All positive and indeterminate samples were then tested using an IgG-specific PF4-H ELISA assay and a platelet serotonin-release assay.

RESULTS

Antibodies to PF4-H were positive in 54 (12.9%) patients using the screening ELISA assay. Nine (2.1%) patients had IgG-specific PF4-H antibodies. None of the patient's had a positive platelet serotonin-release assay. No relationship between hemodialysis access thrombosis and PF4-H antibodies was noted using the screening ELISA assay (unadjusted odds ratio 0.63; 95% CI 0.30-1.30; P = 0.21), the IgG-specific ELISA assay (unadjusted odds ratio 0.83; 95% CI 0.17-4.06; P = 0.82) or indeterminate platelet serotonin-release assay results (unadjusted odds ratio 0.97;95% CI 0.10-9.44;P = 0.98).

CONCLUSIONS

Hemodialysis with repeated exposure to unfractionated heparin was associated with a moderately elevated prevalence of PF4-H antibodies. However, our results do not support a relationship between PF4-H antibodies and hemodialysis vascular access thrombosis.

Pseudo-Pulmonary Embolism as a Sign of Acute Heparin-Induced Thrombocytopenia in Hemodialysis Patients: Safety of Resuming Heparin after Disappearance of HIT Antibodies

Heparin-induced thrombocytopenia (HIT) is a syndrome caused by platelet-activating antibodies that recognize complexes of platelet factor 4 (PF4) and heparin. Thrombocytopenia is the most common clinical feature of HIT. HIT can be considered as a hypercoagulable state, with a high risk of thrombosis. Another feature of HIT is an acute systemic reaction that characteristically begins 5-30 min after receiving an intravenous bolus of unfractionated heparin, such as is commonly given for hemodialysis (HD). Here we present 4 patients who developed acute HIT at or near the start of their chronic HD. All patients were anticoagulated with the low-molecular-weight heparin, nadroparin, for HD. Three of our patients underwent surgery approximately 1-2 weeks before developing HIT. All patients presented with an acute systemic reaction during HD. All patients were treated and further dialyzed with lepirudin. Under this treatment we observed a quick recovery of the platelet count, and patients remained symptom-free. Antibodies against the PF4-heparin complex were detected with a combination of a 'quick test' and an enzyme-linked immunosorbent assay test. The likelihood of having HIT previous to the detection of antibodies was estimated with the pre-test probability score criteria. The tests for PF4-heparin antibodies remained positive for an average of 165 days. Three patients underwent a rechallenge with nadroparin after disappearance of the HIT antibodies in their serum. All 3 remained symptomless when they were further hemodialyzed on nadroparin. Our observations indicate that nadroparin can be successfully reintroduced for HD anticoagulation once the patient's HIT antibodies have disappeared.

HEMATOLOGY: ISSUES IN THE DIALYSIS PATIENT: The Safety of Heparins in End-Stage Renal Disease

In patients on chronic dialysis, unfractionated heparin (UFH) is the most commonly used agent for anticoagulation of the hemodialysis extracorporeal circuit, for hemodialysis catheter "locking" between dialysis treatments, and for nondialysis indications such as venous thromboembolic disease, peripheral vascular disease, and acute coronary artery disease. Potentially serious complications of UFH, such as hemorrhage, osteoporosis, and thrombocytopenia, have led to consideration of other options for anticoagulation, including low molecular weight heparin (LMWH) and direct thrombin inhibitors (DTIs). LMWH can be used for anticoagulation of the hemodialysis circuit, but whether this has significant benefit compared to UFH remains to be proven. Because of the somewhat unpredictable risk of severe bleeding complications when LMWH is used for other indications in dialysis patients, UFH rather than LMWH is preferred for treatment of thromboembolic disease in these patients. DTIs have been used for anticoagulation in dialysis patients with heparin-induced thrombocytopenia (HIT), with argatroban being the preferred agent if heparin-free hemodialysis cannot be performed. UFH still remains the preferred anticoagulant in the vast majority of dialysis patients requiring systemic anticoagulation and for anticoagulation of the extracorporeal hemodialysis circuit.

HEMATOLOGY: ISSUES IN THE DIALYSIS PATIENT: When Heparin Causes Thrombosis: Significance, Recognition, and Management of Heparin-Induced Thrombocytopenia in Dialysis Patients

Heparin-induced thrombocytopenia (HIT) is characterized by thrombocytopenia and paradoxical hypercoagulability. HIT occurs when an antibody ("HIT antibody") produced against the complex of heparin and platelet factor 4 (PF4) causes systemic platelet consumption and activation. Nephrologists encounter HIT in the care of end-stage renal disease (ESRD) patients because heparin is a routine anticoagulant in hemodialysis. The incidence of HIT in ESRD appears to be lower than in other clinical settings. However, HIT is equally life threatening in ESRD patients and therefore demands the same prompt recognition and aggressive treatment. Diagnosing HIT requires the detection of HIT antibodies. A functional assay (e.g., [(14)C] serotonin release assay) relies on the patient's HIT antibodies to activate donor platelets at pharmacologic heparin concentrations. The more common antigen assay (e.g., enzyme-linked immunosorbent assay [ELISA]) detects the binding of the patient's HIT antibodies to antigens (e.g., heparin-PF4 complex) in a microtiter well and does not involve platelets. The moment HIT is suspected, heparin should be stopped and an alternative anticoagulant initiated immediately, even before the result of a serologic test becomes available. The advent of several new anticoagulants in the last decade, especially argatroban and bivalirudin, has expanded treatment options for HIT in dialysis patients. This review discusses the epidemiology, pathogenesis, clinical features, diagnosis, and treatment of HIT, with special emphasis on concepts relevant to the care of dialysis patients.

[Thrombocytopathy and blood complications in uremia]

Bleeding diathesis and thrombotic tendencies are characteristic findings in patients with end-stage renal disease. The pathogenesis of uremic bleeding tendency is related to multiple dysfunctions of the platelets. The platelet numbers may be reduced slightly, while platelet turnover is increased. The reduced adhesion of platelets to the vascular subendothelial wall is due to reduction of GPIb and altered conformational changes of GPIIb/IIIa receptors. Alterations of platelet adhesion and aggregation are caused by uremic toxins, increased platelet production of NO, PGI(2), calcium and cAMP as well as renal anemia. Correction of uremic bleeding is caused by treatment of renal anemia with recombinant human erythropoietin or darbepoetin alpha, adequate dialysis, desmopressin, cryoprecipitate, tranexamic acid, or conjugated estrogens. Thrombotic complications in uremia are caused by increased platelet aggregation and hypercoagulability. Erythrocyte-platelet-aggregates, leukocyte-platelet-aggregates and platelet microparticles are found in higher percentage in uremic patients as compared to healthy individuals. The increased expression of platelet phosphatidylserine initiates phagocytosis and coagulation. Therapy with antiplatelet drugs does not reduce vascular access thrombosis but increases bleeding complications in endstage renal disease patients. Heparin-induced thrombocytopenia (HIT type II) may develop in 0-12 % of hemodialysis patients. HIT antibody positive uremic patients mostly develop only mild thrombocytopenia and only very few thrombotic complications. Substitution of heparin by hirudin, danaparoid or regional citrate anticoagulation should be decided based on each single case.

Argatroban: update

Unfractionated heparin has historically been used as the anticoagulant of choice in the management of a number of thrombotic diseases. Recognition of the limitations of heparin has led to the development of a newer class of anticoagulants, the direct thrombin inhibitors. Argatroban is a synthetic small molecule that selectively inhibits thrombin at its active site. In preclinical studies, argatroban has been shown to be more effective than heparin in preventing arterial thrombosis and in promoting vessel patency in conjunction with thrombolysis in a number of animal models. In clinical trials, argatroban has been shown to be as effective as heparin in the management of ST-segment elevation myocardial infarction in conjunction with thrombolysis. It has been shown to be an effective anticoagulant in patients undergoing percutaneous coronary interventions. In patients with heparin-induced thrombocytopenia and heparin-induced thrombocytopenia complicated by thrombosis, argatroban significantly decreases the risk of thrombotic events. Small studies have demonstrated a potential role for its use in ischemic stroke and hemodialysis. Additional studies are warranted to confirm argatroban's efficacy in a wide variety of clinical settings.

A prospective study of the prevalence of heparin-induced antibodies and other associated thromboembolic risk factors in pediatric patients undergoing hemodialysis

Heparin, which is used at high doses in hemodialysis patients, may induce antibodies favoring thromboembolic complications. We prospectively investigated the prevalence of heparin-induced platelet-reactive antibodies in a cohort of 38 pediatric hemodialysis patients, by means of heparin/platelet factor 4 (H/PF4) ELISA and heparin-induced platelet activation assay (HIPA). We also assessed other acquired and congenital hypercoagulable states. Heparin-induced antibodies were detected in 13 and 21% of patients with HIPA and ELISA, respectively. Anti-H/PF4 antibodies were negatively correlated with the number of hemodialysis sessions. These antibodies disappeared after a median time of 6 months despite continuing heparin treatment. The prevalence of antiphospholipid antibodies was 21% (anticardiolipin 10.5%, anti-beta2GPI 13%, and lupus anticoagulant 5%). Blood levels of homocysteine, factor VIII, and fibrinogen were significantly higher and factor II levels were significantly lower in hemodialysis patients than in controls, whereas factor VII, factor IX, and natural coagulation inhibitor levels were similar in patients and controls. Overall, 26 of 38 patients had at least one biomarker of hypercoagulability, but only 1 patient, without anti-H/PF4 antibodies, presented with thrombosis. In conclusion, heparin induces the transient production of anti-H/PF4 antibodies in children undergoing hemodialysis, but other abnormalities probably contribute to hypercoagulability. These findings may help to improve the diagnosis and management of thrombotic events in hemodialysis patients.

Prevalence of heparin-induced antibodies in patients with chronic renal failure undergoing hemodialysis

Heparin-induced thrombocytopenia (HIT) type II is a serious complication of heparin therapy. It presents initially as thrombocytopenia, and is associated with thrombosis in 20-50% of the cases. HIT is related to the presence of heparin-induced antibodies (HIA), which show specificity for the PF4-heparin (PF4-H) complex. The FcgammaRIIa receptor has been suggested to participate in the pathogenic mechanism of HIA. Since patients undergoing chronic hemodialysis (HD) are exposed repeatedly to heparin, we studied the prevalence of HIA and their eventual relationship with thrombocytopenia and/or thrombosis, and the possible participation of the FcgammaRIIa polymorphism. We studied 207 patients with chronic renal failure (CRF) undergoing HD. As a control we included 130 blood donors and 28 patients with CRF without HD. The HIA patients were studied with the use of a PF4-H ELISA. Additionally, in some positive cases for the previous test, a 14C- serotonin release assay (14C-SRA) was performed. The polymorphism FcgammaRIIa H/R131 was studied by polymerase chain reaction (PCR) with allele-specific primers. Thirty-seven patients (17.9%) undergoing HD presented with HIA. The majority of these antibodies were IgG, IgM, and IgA. The HIA investigated presented specificity against the PF4-H complex, but not against PF4 alone (P<0.001). Twelve out of 22 (54.5%) PF4-H antibodies were positive when tested with the 14C-SRA. The distribution of the FcgammaRIIa polymorphism in patients and healthy controls was 42.6% and 41.6% for H/H131, 41% and 48.9% for the H/R131 isoform, and 16.4% and 9.5% for the R/R131 isoform, respectively. No statistically significant difference in the FcgammaRIIa isoform distribution was found. Twenty-nine out of 156 patients (18.5%) presented thrombocytopenia, and 21/207 (12.4%) had thrombosis of the native vein arterio-venous fistula (AVF). We did not find any statistically significant between HIA and thrombocytopenia or thrombosis. An important proportion of patients with CRF undergoing HD developed HIA, but these cases were not associated with thrombocytopenia or thrombosis of AVF. The frequency of the FcgammaRIIa polymorphism did not statistically differ between HIT type II and normal controls.

Argatroban Anticoagulation in Patients with Heparin-Induced Thrombocytopenia Requiring Renal Replacement Therapy

BACKGROUND:

Argatroban, a direct thrombin inhibitor, is used for prophylaxis or treatment of thrombosis in heparin-induced thrombocytopenia (HIT). The recommended initial dose is 2 μg/kg/min (0.5 μg/kg/min in hepatic impairment), adjusted to achieve activated partial thromboplastin time (aPTT) values 1.5–3.0 times baseline. However, few argatroban-treated patients with HIT and renal failure requiring renal replacement therapy (RRT) have been described.

OBJECTIVE:

To evaluate the safety and efficacy of argatroban anticoagulation during RRT in patients with HIT.

METHODS:

We retrospectively reviewed records from 47 patients with HIT and renal failure requiring RRT who underwent 50 treatment courses with argatroban. Patients with HIT had received argatroban during prospective, multicenter studies. Outcomes, safety, and dosing information were summarized.

RESULTS:

In the multicenter experience, no patient died due to thrombosis and 2 (4%) patients developed new thrombosis while on argatroban. No adverse outcomes occurred during argatroban reexposure. Starting doses were typically 2 μg/kg/min in patients without hepatic impairment and <1.5 μg/kg/min in those with hepatic impairment. Median (range) infusion doses were 1.7 (0.2–2.8) and 0.7 (0.1–1.7) μg/kg/min, respectively, with associated median (range) aPTT ratios, relative to baseline, of 2.2 (1.6–3.6) and 2.0 (1.4–4.1), respectively. Major bleeding occurred in 3 (6%) of 50 treatment courses.

CONCLUSIONS:

Argatroban provides effective anticoagulation upon initial and repeated administration in patients with HIT and renal impairment requiring RRT, with an acceptably low bleeding risk. Current dosing recommendations are adequate for these patients.

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.

A prospective comparison of three argatroban treatment regimens during hemodialysis in end-stage renal disease

BACKGROUND

We prospectively evaluated 3 treatment regimens of argatroban, a direct thrombin inhibitor, for providing adequate, safe anticoagulation in patients with end-stage renal disease (ESRD) during hemodialysis.

METHODS

In this randomized, 3-way crossover study, ESRD patients underwent hemodialysis sessions of 3- or 4-hour duration using high-flux membranes and each of 3 argatroban treatment regimens (A: 250-microg/kg bolus, with an additional 250-microg/kg bolus allowed; B: 250-microg/kg bolus followed by 2-microg/kg/min infusion; C: steady-state, 2-microg/kg/min infusion initiated 4 hours before dialysis). Pharmacodynamic effects including activated clotting times (ACTs); hemodialysis efficacy including single-pool Kt/V, urea reduction ratio (URR), and circuit flow; and safety through a 3-day follow-up were monitored. Argatroban pharmacokinetic parameters including dialytic clearance were evaluated during regimen C.

RESULTS

Thirteen patients completed 38 hemodialysis sessions (1 patient withdrew consent after 2 sessions). Mean +/- SD ACTs increased from 131 +/- 14 seconds at baseline to 153 +/- 24, 200 +/- 30, and 197 +/- 33 seconds, respectively, after 60 minutes of hemodialysis using regimens A, B, and C. Across regimens, mean Kt/Vs (1.5-1.6) and URRs (70%-73%) were comparable. No dialyzer was changed; 1 session was shortened 15 minutes because of circuit clot formation. Systemic argatroban clearance increased approximately 20% during hemodialysis, without clinically significantly affecting ACTs. Upon argatroban discontinuation, ACTs and plasma argatroban decreased concurrently (elimination half-life, 35 +/- 6 min). No thrombosis, bleeding, serious adverse events, or clinically significant changes in vital signs or routine laboratory measures occurred.

CONCLUSION

Argatroban, administered by each treatment regimen, provides safe, adequate anticoagulation to enable successful hemodialysis in ESRD patients. Argatroban dialytic clearance by high-flux membranes is clinically insignificant.

Argatroban and Renal Replacement Therapy in Patients with Heparin-Induced Thrombocytopenia

BACKGROUND:

Argatroban, a direct thrombin inhibitor, is an effective anticoagulant for patients who have heparin-induced thrombocytopenia (HIT). Anticoagulation is usually required for renal replacement therapy (RRT).

OBJECTIVE:

To prospectively evaluate the pharmacokinetics, pharmacodynamics, and safety of argatroban during RRT in hospitalized patients with or at risk for HIT.

METHODS:

Five patients with known or suspected HIT underwent hemodialysis (n = 4) or continuous venovenous hemofiltration (CVVH, n = 1), while receiving a continuous infusion of argatroban 0.5–2 μg/kg/min. Activated partial thromboplastin times (aPTTs), activated clotting times (ACTs), argatroban concentrations (plasma, dialysate, CVVH effluent), and safety were assessed before, during, and after a 4-hour session of RRT. Systemic and dialytic argatroban clearances were calculated.

RESULTS:

Among the 4 hemodialysis patients, aPTT, ACT, and plasma argatroban concentrations remained stable during RRT, with respective mean ± SD values of 74.3 ± 34.2 seconds, 198 ± 23 seconds, and 499 ± 353 ng/mL before RRT, and 70.6 ± 21.4 seconds, 181 ± 12 seconds, and 453 ± 295 ng/mL 2 hours after starting RRT (p values NS). Systemic clearance was 17.7 ± 12.8 L/h before hemodialysis and 17.0 ± 9.5 L/h during hemodialysis (n = 2). The dialyzer clearance (dialysate recovery method) was 1.5 ± 0.4 L/h (n = 4). Generally similar responses occurred in the CVVH patient: systemic argatroban clearance was 4.8 L/h before CVVH and 4 L/h during CVVH. The hemofilter argatroban clearance was 0.9 L/h. No bleeding or thrombosis occurred.

CONCLUSIONS:

Argatroban provides effective alternative anticoagulation in patients with or at risk for HIT during RRT. Argatroban clearance by high-flux membranes during hemodialysis and CVVH is clinically insignificant, necessitating no dose adjustment.

Anticoagulant efficacy of PEG-Hirudin in patients on maintenance hemodialysis

BACKGROUND

Heparins are currently the anticoagulants of choice in long-term hemodialysis (HD). Because of their shortcomings, including the increasing incidence of heparin-induced thrombocytopenia (HIT II), alternative anticoagulation is necessary. The study objectives were to provide safe and effective HD by investigating an appropriate PEG (polyethylene glycol)-Hirudin dosage regimen in patients on HD, as well as to compare the safety, tolerability, and efficacy of PEG-Hirudin with that of unfractionated heparin (UFH).

METHODS

Twenty patients (12 males, 8 females, mean age 57.8 years) with end-stage renal disease (ESRD) took part in the study. Dialysis sessions lasting a mean of 4.3 hours (QB 250 to 300 mL/min, QD 500 mL/min) were performed 3 times a week with a Gambro GFS plus 16 dialyzer. Ten patients (group I) received UFH at 3 regular dialysis sessions (HD1-3) followed by 5 dialysis sessions using PEG-Hirudin (HD4-8). Another 10 patients (group II) received UFH at 3 regular dialysis sessions (HD1-3) followed by 10 sessions on PEG-Hirudin (HD4-13). The starting dose of PEG-Hirudin was a single bolus injection of 80 microg/kg BW (HD4), except for the first patient, who received 50 microg/kg BW followed by a 12 microg/kg bolus. Before each of the following sessions (HD5-13), an individualized PEG-Hirudin dose of between 26 to 65 microg/kg body weight (BW) (mean dose 41 microg/kg BW) was injected. PEG-Hirudin plasma and blood concentrations derived from anti-Iia activity and ecarin clotting time (ECT), respectively, activated partial thromboplastin time (aPTT), bleeding time, and arteriovenous (AV) fistula compression time were investigated to calculate the pharmacokinetic parameters or to assess anticoagulant efficacy.

RESULTS

Mean predialysis PEG-Hirudin plasma concentrations increased up to a maximum of 488 ng/mL in group I (HD8) and up to 536 ng/mL in group II (HD8). Mean plasma concentrations measured at 5 minutes after the 1st (HD4), 5th (HD8), and 10th (HD13) PEG-Hirudin injection ranged from 1076 to 1298 ng/mL. Mean post-dialysis plasma levels ranged from 818 to 995 ng/mL. Mean predialysis aPTT was not affected by UFH, but was prolonged by 46 to 56 seconds by PEG-Hirudin. Five minutes after injecting PEG-Hirudin or UFH, mean aPTT was prolonged to a maximum of 85 and 188 seconds, respectively. Mean post-dialysis aPTT values ranged from 60 to 68 seconds after PEG-Hirudin and 34 to 46 seconds after UFH. PEG-Hirudin was well tolerated; no serious adverse events or bleeding complications were observed. Safety assessments yielded no significant difference between the two anticoagulants.

CONCLUSION

This pilot study confirmed the usefulness and tolerability of a PEG-Hirudin dose regimen consisting of a single, fixed bolus dose of 80 microg/kg BW injected before starting the first dialysis session (HD4) and followed by a dose titration period over at least 4 sessions (HD5-8), which again was followed by a fixed maintenance dose period (HD9-13). On the basis of PEG-Hirudin data from patients with various degrees of renal insufficiency but not undergoing hemodialysis and prior recombinant-hirudin (r-hirudin) experience, patients were titrated into an EC-controlled dose range that proved to be efficacious enough to prevent clotting and safe enough to prevent bleeding. Due to the favorable pharmacokinetic properties of PEG-Hirudin, a residual anticoagulant effect is maintained in the intervals between dialysis sessions, and this permanent state of anticoagulation may prevent vascular access complications as well as other vascular events.

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.

Different effects of enoxaparin and unfractionated heparin on extrinsic blood coagulation during haemodialysis: a prospective study

BACKGROUND

Heparin inhibits prothrombotic tissue factor (TF) and releases its inhibitor, tissue factor pathway inhibitor (TFPI), from the endothelium, but repeated administration of heparin depletes vascular stores of TFPI. We studied the anticoagulant effects of unfractionated heparin (UFH) vs low-molecular-weight enoxaparin-used for thrice-weekly maintenance haemodialysis (HD)-on plasma levels of total TF and TFPI and on those of an activated coagulation marker prothrombin fragment 1+2 (PF 1+2).

METHODS

Twenty-five patients dialysed using a single injection of enoxaparin (at a mean dose of 0.68 mg/kg) were randomly assigned to either receive UFH administered as a mean bolus of 42.1 IU/kg and continuous infusion of 57.8 IU/kg (n=12) or to be maintained on enoxaparin (n=13), and were followed prospectively for 12 weeks. Plasma immunoreactive TF, TFPI and PF 1+2 were measured at the start and after 10 and 180 min of HD, and compared with values in 15 healthy controls.

RESULTS

Pre-dialysis TF, TFPI and PF 1+2 were higher than normal (all P<0.0001). TF and PF 1+2 did not change, while TFPI levels, compared with baseline, increased at each interval in enoxaparin-anticoagulated HD patients (all P<0.0001). TFPI increments correlated inversely with pre-dialysis TFPI (both P<0.0007). In patients switched to UFH, TF levels remained unchanged compared with pre-randomization values, TFPI increased at each interval of HD sessions (all P<0.035) and PF 1+2 increased pre-dialysis (P=0.015). The over-dialysis effects of UFH resembled those of enoxaparin. In contrast, baseline TFPI and its 10-min rise correlated inversely with the UFH loading dose (both P<0.040). Pre-dialysis PF 1+2 was inversely associated with TFPI increments (both P<0.034), and directly with pre-dialysis TFPI (P=0.018) and the UFH loading dose (P=0.045).

CONCLUSIONS

Depletion of heparin-releasable stores of TFPI is an untoward effect of repeated anticoagulation during maintenance HD therapy. The traditional UFH regimen is more prothrombotic than single enoxaparin injections, with high loading doses of UFH being involved in TFPI exhaustion and subsequent hypercoagulability.

Thrombosis in end-stage renal disease

Although renal failure has classically been associated with a bleeding tendency, thrombotic events are common among patients with end-stage renal disease (ESRD). A variety of thrombosis-favoring hematologic alterations have been demonstrated in these patients. In addition, "nontraditional" risk factors for thrombosis, such as hyperhomocysteinemia, endothelial dysfunction, inflammation, and malnutrition, are present in a significant proportion of chronic dialysis patients. Hemodialysis (HD) vascular access thrombosis, ischemic heart disease, and renal allograft thrombosis are well-recognized complications in these patients. Deep venous thrombosis and pulmonary embolism are viewed as rare in chronic dialysis patients, but recent studies suggest that this perception should be reconsidered. Several ESRD treatment factors such as recombinant erythropoietin (EPO) administration, dialyzer bioincompatibility, and calcineurin inhibitor administration may have prothrombotic effects. In this article we review the pathogenesis and clinical manifestations of thrombosis in ESRD and evaluate the evidence that chronic renal failure or its management predisposes to thrombotic events.

The pathophysiology of immune-mediated heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an important side effect of heparin therapy associated with significant morbidity and mortality if unrecognized. The platelet count typically falls below 150,000/ micro l 5-14 days after heparin is started. Thrombosis is the major clinical complication. The diagnosis is confirmed with a variety of functional and antigenic assays. Heparin binds to PF4, resulting in a conformational change in the molecule that exposes neo-epitopes that act as immunogens. Antibodies form against the heparin-PF4 complex, the major target antigen. The IgG-heparin-PF4 immune complex binds either via its Fab domain to the platelet surface or via its Fc domain to the FcgammaIIA receptor on the surface of the platelet, resulting in further platelet activation. Continued release of PF4 from activated platelets leads to increasing PF4-heparin complex formation, and a self-propagating cycle of platelet consumption and generation of procoagulant platelet-derived microparticles. Other procoagulant effects of the HIT antibody include endothelial cell damage, stimulation of platelet-leukocyte aggregates, and release of tissue factor from monocytes.

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.

Long-term citrate anticoagulation for high-flux haemodialysis in a patient with heparin-induced thrombocytopenia type II

For the first time, long-term use of regional citrate anticoagulation for high-flux haemodialysis is reported in a patient with heparin-induced thrombocytopenia type II. A simple, flow-independent, citrate infusion protocol allowed efficient anticoagulation. Excellent solute removal, indicated by KT/V values of 1.52 to 1.98, was achieved. Electrolyte and acid-base balance as well as calcium homeostasis were well controlled over a period of 9 months.

Evolution of oxidative stress and inflammation during hemodialysis and their contribution to cardiovascular disease

End-stage renal disease patients have increased cardiovascular morbidity and mortality. These patients have many unique risk factors, such as an accumulation of uremic toxins, electrolyte imbalances, metabolic disturbances, anemia, chronic inflammation, and thrombogenic disturbances. Oxidative stress has been implicated in many of these disturbances. This review will focus on some of the factors that may accelerate cardiovascular disease in uremic patients, with an emphasis on mechanisms and interactions of various components of oxidative stress and inflammation. Understanding the mechanisms of these pathways may be useful in developing effective prevention and treatment strategies.

The presence of heparin-platelet factor 4 antibodies as a marker of hypercoagulability during hemodialysis

We have assessed the prevalence of heparin-platelet factor 4 antibodies in a group of 100 patients on chronic intermittent hemodialysis with repeated exposure to heparin in order to establish the clinical significance of an immunological response to heparin. Heparin-induced platelet reactivity was studied in a subgroup of 86 patients. Routine laboratory parameters such as plasma C-reactive protein, albumin and immunoglobulins were included. Clinical endpoints were thrombosis in blood access, change of blood access, other thromboembolic events, bleeding complications, falling platelet count, and ischemic vascular disease or death within 1 year of blood sampling. Blood access thrombosis was a frequent complication (26%), often leading to change of dialysis blood access (21%). Antibodies were detected in 3-6% of hemodialysis patients and antibody levels correlated to blood access thrombosis and change of access (p<0.05). An unexpected finding was that of increased heparin-induced platelet reactivity in 36% of the control group of 24 uremic patients prior to dialysis or exposure to heparin. The findings suggest that antibodies to heparin-platelet factor 4 may contribute to hypercoagulability during hemodialysis, leading to thrombotic complications in affected patients.

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.

R-hirudin as anticoagulant in regular hemodialysis therapy: finding of therapeutic R-hirudin blood/plasma concentrations and respective dosages

Recently heparin-induced thrombocytopenia type II has been diagnosed more frequently and does not exclude hemodialysis patients. Up to now, recombinant hirudin is the only available anticoagulant showing no immunologic cross reactions with heparin. However, the use of r-hirudin in hemodialysis patients with different degrees of residual renal functions is impossible using standard dosages because elimination of r-hirudin varies depending on the degree of residual renal function. Therefore the first study was carried out using consecutive r-hirudin anticoagulated hemodialyses to determine the appropriate dose of r-hirudin. Ten hemodialysis patients with creatinine clearance values ranging between 0 and 13 mL/min/1.73m2 were anticoagulated with r-hirudin. An initial bolus of 0.1 mg/kg bwt before the first hemodialysis, resulted in an average r-hirudin blood concentration of 305 ng/mL at the end of treatment. The dose for each of the following four hemodialyses was adjusted individually to reach the minimum therapeutic r-hirudin blood concentration. At the end of these treatments the mean blood r-hirudin concentration was 422 ng/mL. The necessary mean doses ranged between 0.008 and 0.125 mg/kg bwt correlating to the creatinine clearance values of the patients. All hemodialyses of the study were effective and safe. Bleeding times determined during r-hirudin anticoagulation were significantly lower than control values measured 2 days after a heparin administration. The study proved that r-hirudin may be an efficient and safe heparin alternative as a hemodialysis anticoagulant when the individual's residual renal function is noted for dosage and dose adjustment and is controlled by drug monitoring using the ecarin clotting time.