John G. Kelton

Heparin-Induced Thrombocytopenia in Patients Treated with Low-Molecular-Weight Heparin or Unfractionated Heparin

BACKGROUND Heparin-induced thrombocytopenia, defined by the presence of heparin-dependent IgG antibodies, typically occurs five or more days after the start of heparin therapy and can be complicated by thrombotic events. The frequency of heparin-induced thrombocytopenia and of heparin-dependent IgG antibodies, as well as the relative risk of each in patients given low-molecular-weight heparin, is unknown. METHODS We obtained daily platelet counts in 665 patients in a randomized, double-blind clinical trial comparing unfractionated heparin with low-molecular-weight heparin as prophylaxis after hip surgery. Heparin-induced thrombocytopenia was defined as a decrease in the platelet count below 150,000 per cubic millimeter that began five or more days after the start of heparin therapy, and a positive test for heparin-dependent IgG antibodies. We also tested a representative subgroup of 387 patients for heparin-dependent IgG antibodies regardless of their platelet counts. RESULTS Heparin-induced thrombocytopenia occurred in 9 of 332 patients who received unfractionated heparin and in none of 333 patients who received low-molecular-weight heparin (2.7 percent vs. 0 percent; P = 0.0018). Eight of the 9 patients with heparin-induced thrombocytopenia also had one or more thrombotic events (venous in 7 and arterial in 1), as compared with 117 of 656 patients without heparin-induced thrombocytopenia (88.9 percent vs. 17.8 percent; odds ratio, 36.9; 95 percent confidence interval, 4.8 to 1638; P < 0.001). In the subgroup of 387 patients, the frequency of heparin-dependent IgG antibodies was higher among patients who received unfractionated heparin (7.8 percent, vs. 2.2 percent among patients who received low-molecular-weight heparin; P = 0.02). CONCLUSIONS Heparin-induced thrombocytopenia, associated thrombotic events, and heparin-dependent IgG antibodies are more common in patients treated with unfractionated heparin than in those treated with low-molecular-weight heparin.

Comparison of Plasma Exchange with Plasma Infusion in the Treatment of Thrombotic Thrombocytopenic Purpura

BACKGROUND Thrombotic thrombocytopenic purpura is an uncommon disease with a high mortality rate even with current treatment. The cause of the syndrome and its optimal treatment are unknown. Although both plasma exchange and plasma infusion have been useful treatments, it is not clear which is superior. In this report we describe a prospective randomized trial comparing plasma exchange with plasma infusion for the treatment of thrombotic thrombocytopenic purpura. METHODS One hundred two patients with thrombotic thrombocytopenic purpura were randomly assigned to receive either plasma exchange or plasma infusion with fresh-frozen plasma on seven of the first nine days after entry into the trial. The total volume of plasma received by patients undergoing plasma exchange was three times that received by patients undergoing plasma infusion. All the patients also received aspirin and dipyridamole. The outcomes in the two groups were compared at the end of the first treatment cycle (day 9) and after six months. RESULTS At the end of the first treatment cycle patients receiving plasma exchange had a higher rate of response as defined by an increase in the platelet count (24 of 51 patients) than those who received plasma infusion (13 of 51, P = 0.025). Of the 51 patients treated with plasma exchange, 2 died, whereas 8 of the 51 patients who received plasma infusion died (P = 0.035). After six months the outcome in the plasma-exchange group was still superior, with a response observed in 40 of 51 patients, whereas 25 of 51 patients in the plasma-infusion group responded (P = 0.002). Eleven patients in the plasma-exchange group died, as did 19 patients in the plasma-infusion group (P = 0.036). The overall mortality was 29 percent. CONCLUSIONS Plasma exchange is more effective than plasma infusion in the treatment of thrombotic thrombocytopenic purpura.

A 14-year study of heparin-induced thrombocytopenia

PURPOSE To determine the sites of thromboses (venous versus arterial circulation) that complicate the clinical course of immunemediated heparin-induced thrombocytopenia, and to determine the 30-day risk for thrombosis in patients who are initially recognized with isolated heparin-induced thrombocytopenia. PATIENTS AND METHODS We analyzed objectively documented thrombotic events that complicated the clinical course of 127 patients with serologically confirmed heparin-induced thrombocytopenia identified in one medical community over a 14-year period. We classified heparin-induced thrombocytopenia patients into two groups: patients recognized with heparin-induced thrombocytopenia only after a new thrombosis had occurred, and patients initially recognized with isolated heparin-induced thrombocytopenia. We determined the subsequent 30-day risk for thrombosis for the cohort of patients initially recognized with isolated thrombocytopenia. RESULTS Heparin-induced thrombocytopenia was associated with the development of new venous thrombotic events and arterial thrombotic events in 78 and 18 patients, respectively (ratio venous/arterial thrombosis = 4:1). Pulmonary embolism was the most common life-threatening thrombotic event, occurring in 25% of all patients. Approximately half of all heparin-induced thrombocytopenia patients were recognized only after they had a complicating thrombotic event. Of the remaining 62-patient cohort initially recognized with isolated thrombocytopenia, the subsequent 30-day risk of thrombosis was 52.8%. The risk of thrombosis did not differ whether the heparin had been discontinued alone or whether warfarin had been substituted for the heparin. CONCLUSIONS Venous thrombosis complicates heparin-induced thrombocytopenia more frequently than does arterial thrombosis. The high risk of thrombosis in patients initially recognized with isolated thrombocytopenia suggests that conventional management approaches require reappraisal.

Temporal aspects of heparin-induced thrombocytopenia.

Background Heparin-induced thrombocytopenia is a relatively common antibody-mediated drug reaction. We studied the temporal relation between previous or current heparin therapy and the onset of heparin-induced thrombocytopenia. Methods We examined the time between the start of heparin therapy and the onset of thrombocytopenia in 243 patients with serologically confirmed heparin-induced thrombocytopenia. We also investigated the persistence of circulating heparin-dependent antibodies by performing a platelet serotonin-release assay and an assay for antibodies against platelet factor 4. The outcome in seven patients who had previously had an episode of heparin-induced thrombocytopenia and were later treated again with heparin was also examined. Results A fall in the platelet count beginning four or more days after the start of heparin therapy occurred in 170 of the 243 patients (70 percent); in these patients, a history of previous heparin treatment did not influence the timing of the onset of thrombocytope...

Heparin-Associated Thrombocytopenia

Heparin-associated thrombocytopenia is a relatively common complication of heparin therapy occurring in approximately 5% of the patients who receive this drug. The incidence is higher with bovine heparin then with porcine heparin. Onset of heparin-associated thrombocytopenia usually occurs 6 to 12 days after initiation of treatment and by itself has a low morbidity. Heparin-associated thrombocytopenia plus arterial thrombosis can cause major complications including stroke, heart attack, and death. The incidence of heparin-associated thrombocytopenia plus arterial thrombosis is lower than that for heparin-associated thrombocytopenia alone. The diagnosis of heparin-associated thrombocytopenia remains one of exclusion, but testing for the presence of a heparin-dependent platelet-aggregating factor may prove to be useful. Analysis of the time of onset suggests a strategy for prevention. Oral anticoagulants could be started concomitantly with the heparin so that it could be discontinued in several days. This approach may prevent most episodes of heparin-associated thrombocytopenia.

Systematic Review: Efficacy and Safety of Rituximab for Adults with Idiopathic Thrombocytopenic Purpura

Idiopathic thrombocytopenic purpura (ITP) is a common hematologic disorder characterized by platelet autoantibodies, low platelet counts, and bleeding. Rituximab is a chimeric, monoclonal anti-CD20 antibody that targets B lymphocytes and causes Fc-mediated cell lysis (14). It is currently indicated for the treatment of lymphoma (58), but because of its ability to deplete autoantibody-producing B lymphocytes and its favorable toxicity profile (9), it has been used in patients with various autoimmune diseases (1012), including ITP. In some patients with ITP, rituximab has been associated with a reduction in specific platelet-associated autoantibodies and an increase in platelet count (13). Early success with rituximab in ITP has lead to its widespread use and incorporation into recent treatment algorithms (14, 15). However, the evidence to support the use of rituximab in ITP is uncertain. We performed a systematic review of the literature to evaluate the efficacy and safety of this treatment. Methods Search Strategy One hematologist and one internist independently searched the literature in June 2005 and updated the search in April 2006. The electronic databases of MEDLINE (from 1966) and EMBASE (from 1980) were searched by using the explode function for the Medical Subject Heading (MeSH) terms antibodies, monoclonal and purpura, thrombocytopenic, idiopathic and the textwords rituximab, rituxan, mabthera, anti CD20, anti CD20 antibody, immune thrombocytopenic purpura, and idiopathic thrombocytopenic purpura. The MEDLINE database was also searched with the PubMed search engine by using the MeSH term purpura, thrombocytopenic, idiopathic and the textwords rituximab and rituxan. The Cochrane Registry for Controlled Trials was searched by using the terms rituximab, immune thrombocytopenic purpura, and ITP. Scientific abstracts were identified by searching the electronic databases of the American Society of Hematology and the American Society of Clinical Oncology from 1997 (the year of licensure of rituximab) to 2005 by using the search terms ritux*, thrombocytopenic, and ITP. Bibliographies of relevant articles and reviews were manually searched, and authors were canvassed for additional citations. Eligibility Criteria and Study Selection Exclusion criteria were secondary causes of thrombocytopenia, including splenomegaly, hepatitis B or C virus infection, HIV infection, lupus, antiphospholipid antibody syndrome, bone marrow failure syndromes, and drug-induced thrombocytopenia; malignancy, including chronic lymphocytic leukemia and lymphoma; the Evan syndrome; and rituximab re-treatments. Children (<16 years of age) were excluded because the biology and natural history of ITP in children were believed to differ considerably from those in adults. There was no restriction on study design or language of publication. Reports published only in abstract form were eligible. Where duplicate or redundant publications were uncovered, the latest and most informative version was retained. Initially, titles and abstracts of all articles were evaluated independently by 2 reviewers. Full-text articles were retrieved when they were judged by at least 1 reviewer to possibly contain relevant original data. Final article selection was done independently by both reviewers, and disagreements were resolved by consensus in all cases. Data Extraction The following data were collected in duplicate: proportion of patients with complete, partial, or minimal platelet count responses (and their definitions); time to platelet count responses; duration of platelet count responses; dose and schedule of rituximab administration; toxicities; previous ITP treatments; baseline platelet count; duration of ITP before rituximab treatment; study design and use of controls; and sources of funding. Individual-patient data were used where possible. Assessment of Methodologic Quality Study quality was assessed independently by 2 hematologists with expertise in research methods. Reviewers evaluated 4 key design features for each study: prospective data collection, consecutive patient enrollment, a clearly stated duration of follow-up, and a description of losses to follow-up. Assessors were blinded to study author, journal, publication date, and main results. Disagreements were resolved by independent adjudication. Statistical Analysis Patient demographic characteristics and platelet count responses were analyzed only from those studies enrolling 5 or more patients because we felt that smaller studies may be subject to extreme reporting bias. To determine estimates of response, we defined complete response as the achievement of a platelet count greater than 150109 cells/L; partial response as a platelet count between 50 and 150109 cells/L; and overall response as a platelet count greater than 50109 cells/L. These definitions were chosen to reflect the most common criteria used in primary reports. Toxicities were considered from all studies, including those enrolling fewer than 5 patients each, to provide the most thorough description of safety. We determined estimates of effect of rituximab by calculating the weighted mean proportion by using a random-effects model. This model estimated the between-study variance by using the method of moments and assumed that the proportion from each study was sampled from the normal distribution, with variance calculated from the data. Continuous variables, including time to response, response duration, and follow-up, were summarized with medians, minimum and maximum values, and interquartile ranges assuming a normal distribution of the data. Unweighted chance-corrected values were used to assess agreement between reviewers for study selection (16). Role of the Funding Source This systematic review had no external source of funding. The organizations that fund the individual authors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, and approval of the manuscript. Results Study Selection We identified 599 citations through our comprehensive literature search, of which 60 were retrieved for detailed review (Figure 1). Agreement between reviewers for initial study inclusion was excellent (= 0.87). After exclusion of ineligible studies, redundant or duplicate publications, and reports that did not contain original data, 31 reports were included. Nineteen studies (313 patients) enrolled at least 5 patients each and were included in the efficacy analysis (13, 1734), and 29 studies (306 patients) reported toxicity data (13, 1719, 2128, 3046). Of the 19 reports describing efficacy outcomes, 9 were published in abstract form only. Abstracts were carefully scrutinized, and authors were contacted when necessary to ensure that redundant publications were excluded. Figure 1. Article selection. Results of article search and selection conducted in accordance with guidelines on reporting systematic reviews of observational studies (56). ITP = idiopathic thrombocytopenic purpura. Study Designs and Sources of Funding There was 1 dose-finding phase II study (28) and 18 single-arm cohort studies (13, 1727, 2934). Source of funding was not reported in 26 of 31 reports; of the remaining 5, 1 was industry-sponsored (19), 3 were funded by nonprofit organizations (21, 31, 41), and 1 reported that it had no funding information to disclose (32). Description of Patients Patients were 16 to 89 years of age, had had ITP for 1 to 360 months, and had a platelet count that ranged from 1 to 89109 cells/L before rituximab treatment (Table 1). Nearly all (99.0%) patients had received corticosteroids, and 158 (50.5%) had had splenectomy. Other previous treatments were immunosuppressants, including cyclosporine, azathioprine, or mycophenylate (n= 26); cyclophosphamide (n= 12); vinca alkaloids (n= 18); and danazol (n= 17). The number of previous treatments varied between and within reports. Table 1. Characteristics of Patients with Idiopathic Thrombocytopenic Purpura in Rituximab Studies Enrolling 5 or More Patients Each (n= 313)* Rituximab Dose and Schedule Rituximab was administered as a weekly infusion of 375 mg/m2 for 4 consecutive weeks in 16 of 19 studies. Of the remaining 3 studies, 1 did not report the dosing schedule (30); 1 used a schedule of 1 to 8 infusions of 325 mg/m2 per dose (29); and 1 used a low dose of rituximab (50 mg/m2 on day 1, then 150 mg/m2 on days 8 and 15), an intermediate dose (150 mg/m2 on day 1, then 375 mg/m2 weekly for 3 weeks), and a standard dose (28). Platelet Count Response In most reports, complete response and partial response were defined according to the achievement of predefined platelet count thresholds; however, these thresholds varied. Certain reports used additional criteria to define a response, including the discontinuation of steroid therapy (32) and the resolution of bleeding symptoms (26). One report defined complete response as the achievement of a platelet count that was adequate for hemostasis (25); in 2 reports, neither complete response nor partial response was defined (22, 27). The timing of platelet count measurements in the definitions of a response was specified in 2 reports: 12 weeks after the first rituximab infusion (29) and 2 weeks after the last infusion (30). In 1 report, a response was considered only if it lasted at least 30 days (21), and in another, at least 4 months (13). Where reporting of studies included homogenous criteria to define platelet count responses to therapy, treatment with rituximab resulted in a complete response (platelet count> 150109 cells/L) in 46.3% of patients (95% CI, 29.5% to 57.7%), partial response (50 to 150109 cells/L) in 24.0% (CI, 15.2% to 32.7%), and overall response (>50109 cells/L) in 62.5% (CI, 52.6% to 72.5%). Rates of complete, partial, and overall response were based on 191, 284, and 313 eligible patients, respectively (Table 2). In a sensitivity analysis that exclud

The Role of the Plasma from Platelet Concentrates in Transfusion Reactions

BACKGROUND Febrile, nonhemolytic transfusion reactions are the most frequent adverse reactions to platelets. A number of observations argue against the widely held view that these reactions result from the interaction between antileukocyte antibodies in the recipient and leukocytes in the platelet product. We sought to determine whether substances in the plasma or the cells in the product cause reactions to transfused platelets. METHODS We separated standard platelet concentrates into their plasma and cellular components and then transfused both portions in random order. Patients were monitored for reactions during all transfusions. Before each transfusion, the concentration of cytokines (interleukin-1 beta and interleukin-6) was measured in the platelet products. Studies were also performed on the platelet products to determine the effect of storage on the concentration of cytokines. RESULTS Sixty-four pairs of platelet-product components (the plasma supernatant and the cells) were administered to 12 patients. There were 20 reactions to the plasma supernatant and 6 reactions to the cells (chi-square = 6.50, P = 0.009). Eight transfusions were associated with reactions to both products. The plasma component was more likely to cause severe reactions than the cells (chi-square = 9.6, P < 0.01). A strong positive correlation was observed between the reactions and the concentration of interleukin-1 beta and interleukin-6 in the plasma supernatant (P < 0.001 and P = 0.034, respectively). In vitro studies demonstrated that interleukin-1 beta and interleukin-6 concentrations rise progressively in stored platelets and that these concentrations are related to the leukocyte count in the platelet product. CONCLUSIONS Bioreactive substances in the plasma supernatant of the platelet product cause most febrile reactions associated with platelet transfusions. Removing the plasma supernatant before transfusion can minimize or prevent these reactions.

The Pathogenesis of Venous Limb Gangrene Associated with Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia is one of the most important immunologic drug reactions that physicians must manage. It is caused by a platelet-activating, heparin-dependent IgG antibody and is an important cause of paradoxical arterial and venous thrombotic complications [1-5]. Acute arterial occlusion is an important cause of limb loss in some patients with heparin-induced thrombocytopenia [1, 6-11]. After we observed a patient with heparin-induced thrombocytopenia and deep venous thrombosis develop distal ischemic limb necrosis in the absence of arterial occlusion (venous limb gangrene), we retrospectively reviewed all of our patients with serologically confirmed heparin-induced thrombocytopenia to investigate this problem. We identified eight patients with venous limb gangrene. Each of these patients had a consistent course of events: heparin-induced thrombocytopenia and deep venous thrombosis followed by venous limb gangrene that developed when heparin therapy was discontinued and warfarin therapy was either initiated or continued. Warfarin is a commonly used oral anticoagulant that reduces functional levels of four vitamin K-dependent procoagulant factors: II, VII, IX, and X [12]. Warfarin also reduces levels of two vitamin K-dependent anticoagulant factors: protein C and protein S [12]. Warfarin anticoagulation can cause paradoxical thrombotic events, particularly central skin necrosis in patients with congenital heterozygous protein C deficiency [13-16]. It has been postulated that warfarin-induced skin necrosis is caused by a transient prothrombotic state that results from a faster reduction in the level of the major natural anticoagulant factor (protein C; half-life, 6 hours) than in the level of the major procoagulant factor (prothrombin; half-life, 72 hours). In this report, we describe a novel syndrome in which patients with acute heparin-induced thrombocytopenia and deep venous thrombosis who are treated with warfarin seem to be at risk for developing venous limb gangrene. Laboratory studies suggest that this syndrome is related to a warfarin-induced failure of the protein C anticoagulant pathway to regulate the increased thrombin generation that occurs in patients with heparin-induced thrombocytopenia. Methods Case-Control Studies In the first of two casecontrol studies, we compared patients with heparin-induced thrombocytopenia who developed venous limb gangrene with patients with heparin-induced thrombocytopenia who developed acute limb arterial thrombosis. In the second casecontrol study, we compared patients who developed venous limb gangrene with patients who did not develop venous limb gangrene during warfarin treatment of heparin-induced thrombocytopenia and deep venous thrombosis. Patients Case-patients and controls were identified from review of the clinical and laboratory records of all 158 patients treated for heparin-induced thrombocytopenia (platelet count nadir, <150 109/L) in one of the five Hamilton, Ontario, hospitals during a 15-year period that ended on 31 December 1994. The diagnosis of heparin-induced thrombocytopenia was confirmed serologically in all patients [17, 18]; 133 patients had been included in previous studies [3, 19]. Four patient summaries are included in this report; three of the four patients had venous limb gangrene (patients 1, 2, and 3), and one patient had severe venous limb ischemia that resolved on reversal of warfarin treatment with vitamin K and plasmapheresis (patient 4). Definitions Limb arterial thrombosis was defined as abrupt arterial occlusion of a limb with absent pulses and was verified in all patients by angiography or surgical thrombectomy. Venous limb gangrene was defined as distal ischemic tissue necrosis complicating deep venous thrombosis despite palpable or Doppler-identifiable arterial pulses. Deep venous thrombosis was confirmed by contrast venography or duplex compression ultrasonography in all patients. All pathologic material was reviewed to evaluate the types of vessels involved in the thrombotic process. Central skin necrosis was defined as skin necrosis that occurred in the breast, abdomen, buttocks, or thigh in association with warfarin treatment. Coagulation Studies Serial citrated plasma samples were available from 34 consecutive patients with heparin-induced thrombocytopenia who were treated at one hospital over a 2-year period. These samples were collected and tested according to a local study protocol approved by the hospitals institutional review board. Before testing, all samples were stored in aliquots frozen at 70C. Four of the 34 patients (including patients 2, 3, and 4) developed venous limb gangrene or severe venous limb ischemia; this allowed us to test the hypothesis that warfarin therapy could contribute to venous limb gangrene. Control studies were done by using plasma obtained during a clinical trial of heparin prophylaxis [3] from 59 patients with deep venous thrombosis but not heparin-induced thrombocytopenia. We used one-stage assay techniques to measure levels of the following vitamin K-dependent procoagulant factors: prothrombin (factor II), factor VII, and factor X [20]. Protein C activity was determined by using a functional assay from Diagnostica Stago (Wellmark Diagnostics Ltd., Guelph, Ontario, Canada). Free protein S levels were measured by precipitation of the protein S bound to C4b-binding protein with polyethylene glycol [21]; the supernatant that contained the free protein S was measured by enzyme-linked immunosorbent assay [22] using antibodies to protein S (Affinity Biologicals, Hamilton, Ontario, Canada). Thrombin-antithrombin complex levels were determined by using an enzyme-linked immunosorbent assay [23] (Behring Diagnostics, Montreal, Quebec, Canada) to evaluate in vivo thrombin generation [24]. Antithrombin was measured by use of a chromogenic factor Xa inhibition method (Chromogenix, Helena Laboratories, Mississauga, Ontario, Canada) [25]. Evaluation for factor V Leiden was performed by using a functional assay for resistance to activated protein C [26] and by direct demonstration of the mutation at the DNA level [27]. Statistical Analysis We used both quantitative and qualitative measures to compare groups. Because quantitative measures tended to have skewed distributions, medians rather than means were used as summary statistics and in comparisons between groups. The Mann-Whitney test was used to compare medians, and associated nonparametric methods [28] were applied to estimate 95% CIs on differences between medians (MINITAB Release 10.5, Xtra software, Minitab, Inc., State College, Pennsylvania). Binary variables were summarized as proportions and were compared between groups by using the Fisher exact test [29]. Differences between groups for the binary variables were represented as risk ratios with CIs according to the method of Thomas [30]. For cases in which the risk ratio was zero or infinite, StatXact (Cytel Software Corp., Cambridge, Massachusetts) was used to calculate the exact 95% CIs for the odds ratios. The nonzero upper or lower bound that StatXact computed was then used to produce a quadratic Equation that, when solved, provided the expected event count for the first comparison group. The corresponding upper or lower bound for the risk ratio was then calculated by recomputing the 2 2 frequency table. Selected Case Reports Patient 1 A 56-year-old woman developed heparin-induced thrombocytopenia (platelet count nadir, 37 109/L) that was recognized on day 8 of intravenous heparin therapy given for bilateral, idiopathic proximal deep venous thrombosis of the lower limbs and pulmonary embolism. Heparin therapy was discontinued that day, and 20 mg of warfarin was given daily for 2 consecutive days. The following day, the patient had an international normalized ratio (INR) of 9.4 and developed necrosis involving eight toes, despite palpable pedal pulses (Figure 1). The patient was managed conservatively; sloughing of the gangrenous tissues was followed by healing without the need for amputation. Figure 1. Gangrene of lower-limb digits in patient 1. Patient 2 A 49-year-old woman received treatment with heparin and warfarin for 19 days because of idiopathic proximal deep venous thrombosis of the left lower limb. At that time, progressive symptoms of pain and swelling in the left lower limb prompted measurement of the platelet count, which was found to be 69 109/L (nadir); heparin therapy was discontinued. The INR was therapeutic at 2.2, and warfarin, 7.5 mg/d, was given for the next 2 days. The platelet count returned to normal within 4 days of discontinuation of heparin therapy. However, venous limb gangrene involving the distal left foot was first seen on the third day after heparin therapy ended (Figure 2 A). The INR was 7.2, protein C activity was less than 0.01 U/mL (normal, 0.65 to 1.29 U/mL), and free protein S level was markedly reduced (0.06 U/mL; normal, 0.24 to 0.62 U/mL). The prothrombin level was only moderately reduced (0.26 U/mL; normal, 0.5 to 1.6 U/mL), and thrombin-antithrombin complex levels were elevated (16.6 ng/mL; normal, <4.2 ng/mL). The patient required a below-the-knee amputation. Occlusive venous thrombi were noted in small venules and medium-sized veins, and arteries were normal (Figure 2 B, C, and D). Figure 2. Findings in patient 2. Patient 3 A 35-year-old woman received heparin prophylaxis for injuries sustained in a motor vehicle accident. She had no fractures or soft tissue injury to her left lower limb; she developed proximal deep venous thrombosis of the left lower limb on day 8 of subcutaneous heparin prophylaxis in association with a decrease in platelet count from 216 10 (9)/L (day 6) to 144 109/L (day 7). however, heparin-induced thrombocytopenia was not suspected, and intravenous therapeutic-dose heparin was started; the platelet count measured 3 days later was 30 10 (9)/L (platelet count nadir, 20 109/L). Heparin therapy was discontinued

Delayed-Onset Heparin-Induced Thrombocytopenia and Thrombosis

Heparin-induced thrombocytopenia is an immunologic drug reaction characterized by paradoxical association with venous and arterial thrombosis (1, 2). The syndrome is usually caused by IgG antibodies that are reactive against complexes of platelet factor 4 and heparin (3). Patients typically develop thrombocytopenia while receiving heparin; the peak onset is 5 to 8 days after starting heparin therapy (2). In this report, we describe 12 patients who experienced thrombocytopenia or symptoms of thrombosis an average of 9 days after all heparin was withdrawn. We refer to this phenomenon as delayed-onset heparin-induced thrombocytopenia. Representative Case Report Patient 1 A 68-year-old woman underwent laparoscopic cholecystectomy. She received one preoperative and two postoperative subcutaneous 5000-U injections of unfractionated heparin before discharge on postoperative day 1. Eight days later, she returned to the hospital because of sudden onset of severe anterograde and retrograde amnesia; her platelet count was 50 109 cells/L. The anterograde amnesia cleared within 6 hours, consistent with transient global amnesia. Although no heparin was given, the platelet count decreased further to 14 109 cells/L (nadir); the patient developed ischemia of the left great toe and disseminated intravascular coagulation. The fibrinogen level was 1.1 g/L (normal, 1.5 to 4.5 g/L), the d-dimer level exceeded 3000 g/L (normal, <500 g/L), and thrombinantithrombin complexes were greater than 60 g/L (normal, <4 g/L). Heparin-induced thrombocytopenia was diagnosed, and an 11-day course of danaparoid was associated with resolution of the ischemic symptoms and signs. Twenty-four days after withdrawal of danaparoid, and during persisting thrombocytopenia (platelet count, 94 109 cells/L), the patient developed proximal deep venous thrombosis. She received a 40-day course of danaparoid, with clinical resolution. However, 100 days after stopping the second course of danaparoid, and during persisting thrombocytopenia (platelet count, 109 109 cells/L), symptomatic deep venous thrombosis recurred. The patient received additional danaparoid for 8 days, with overlapping warfarin for 6 months. Six months after heparin-induced thrombocytopenia began, the platelet count remained above 150 109 cells/L. The patient was well at 1-year follow-up. Results of laboratory tests were strongly positive for heparin-dependent antibodies. The patients serum specimen caused 94% serotonin release at 0 U of heparin per mL, 100% serotonin release at 0.2 U of heparin per mL, and 0% serotonin release at 100 U of heparin per mL. In addition, platelet factor 4heparin IgG antibodies were detected by enzyme immunoassay (1.95 optical density units [positive result, >0.45 optical density units]). Antibodies could be detected in blood specimens obtained up to 9 months after the onset of heparin-induced thrombocytopenia; subsequent specimens yielded negative results. Serology for antiphospholipid antibodies (nonspecific inhibitor and anticardiolipin antibodies), as well as levels of antithrombin III, protein C, and protein S (measured after discontinuation of warfarin therapy), had normal results. Factor V Leiden mutation was not present. Methods Patients Our study included patients who had thrombocytopenia and thrombotic events 5 or more days after withdrawal of heparin. We chose a minimum 5-day interval between the last heparin use and onset of thrombocytopenia (for inpatients) or onset of symptoms of thrombosis (for outpatients) because we expected that almost all heparin, whether given intravenously or subcutaneously, would have cleared by this time. Six patients were identified in university-affiliated hospitals in Hamilton, Ontario, Canada, among approximately 180 consecutive patients with serologically confirmed heparin-induced thrombocytopenia. In addition, 3 patients were identified in secondary care hospitals and were then referred for further management at a Hamilton hospital, and 3 patients were identified in other secondary care hospitals during discussions with physicians who referred blood samples for diagnostic testing because of atypical presentations of heparin-induced thrombocytopenia. Laboratory Testing We performed two tests for heparin-dependent antibodies: the platelet serotonin-release assay (4) and an enzyme immunoassay that detects IgG antibodies that are reactive against platelet factor 4heparin complexes (5, 6). We compared the 12 patient serum specimens with 24 randomly chosen control specimens from patients with heparin-induced thrombocytopenia that were matched for year of diagnosis and had been stored at 70 C. Heparin-dependent platelet activation was measured at an unfractionated heparin concentration of 0.2 U/mL (final), whereas heparin-independent platelet activation was measured without addition of heparin. Statistical comparison of the serologic results between patients with delayed-onset and those with typical heparin-induced thrombocytopenia was made by using the t-test (Quattro Pro 8 [1997], Corel Corp., Ottawa, Canada). The institutional review board at McMaster University approved the investigational protocol. Results Clinical Outcomes The Table summarizes the characteristics of 12 patients with delayed-onset heparin-induced thrombocytopenia. Thrombocytopenia and associated clinical sequelae began an average of 9.2 days (range, 5 to 19 days) after the last use of unfractionated heparin (no patients had received low-molecular-weight heparin). For all 6 inpatients, serial platelet counts decreased beginning at least 5 days after heparin withdrawal. Associated thrombotic events began an average of 8.3 days (range, 5 to 14 days) after heparin was withdrawn. Six outpatients developed thrombosis symptoms an average of 10.0 days (range, 6 to 19 days) after hospital discharge. For 8 of the 12 patients, the preceding period of heparin use that led to immune sensitization was 3 or fewer days. Four patients received heparin by subcutaneous injections. Table. Twelve Patients with Heparin-Induced Thrombocytopenia and Thrombosis Beginning after Discontinuation of Heparin Therapy All 12 patients developed one or more thrombotic complications. Venous thromboembolism occurred in 9 patients (3 with pulmonary embolism). Other complications (in 1 patient each) were bilateral lower limb artery thrombosis, postoperative occlusion of a vascular graft, digital ischemia, warfarin-associated venous gangrene, and adrenal infarction. Nine patients received additional heparin for the thrombosis, and all had further decreases in platelet count. One patient developed cardiac arrest 15 minutes after receiving the heparin bolus. Serologic Studies On both assays, serum specimens from the 12 patients with delayed-onset heparin-induced thrombocytopenia yielded strongly positive results for heparin-dependent antibodies (Figure). The patient specimens produced significantly greater heparin-dependent platelet activation at serial dilutions compared with control specimens. In addition, the 12 patient specimens produced significantly greater heparin-independent platelet activation than control specimens. Figure. Figure. Serum specimens from 12 patients with delayed-onset heparin-induced thrombocytopenia. Top. gray bars white bars Bottom. P P P P P Discussion We discuss 12 patients with an unusual presentation of heparin-induced thrombocytopenia, characterized by delayed onset of thrombocytopenia and thrombosis, that began a mean of 9.2 days (range, 5 to 19 days) after withdrawal of all heparin. Many thrombotic and other complications occurred. Venous thromboembolism (n = 9) and thrombosis of arteries or arterial grafts (n = 2) were the most common; other unusual sequelae included adrenal hemorrhagic infarction, warfarin-associated venous limb gangrene, and transient global amnesia (2). Three of the 12 patients (25%) had disseminated intravascular coagulation severe enough to be associated with depletion of fibrinogen. This is a rare complication of heparin-induced thrombocytopenia (2, 7), but we believe it may be more common in patients with delayed-onset heparin-induced thrombocytopenia. In such patients, the heparin has left the circulation, allowing unopposed thrombin generation (8, 9) due to effects of procoagulant platelet-derived microparticles (1012). Our serologic studies showed that patients with delayed-onset heparin-induced thrombocytopenia have high-titer platelet-activating antibodies that exhibit increased heparin-dependent and heparin-independent platelet activation. It has been established that heparin-dependent antibodies recognize one or more sites on platelet factor 4 (5, 13) that are conformationally modified by pharmacologic heparin or endogenous glycosaminoglycans, such as endothelial-bound heparan sulfate (14, 15). Therefore, delayed-onset heparin-induced thrombocytopenia could be caused by high titers of heparin-dependent antibodies that recognize platelet factor 4 bound to the platelet surface in the absence of residual pharmacologic heparin, platelet factor 4 bound to endothelial glycosaminoglycans, or both. Because our study is small, we cannot draw definitive conclusions about optimal treatment. Recent consensus recommendations state that heparin-induced thrombocytopenia should be treated with an agent that reduces thrombin generation (16, 17). In our study, patients who received an agent that inhibits either coagulation factor Xa (danaparoid) or thrombin (argatroban) seemed to have better outcomes than patients treated with ancrod, a defibrinogenating snake venom (18) that does not reduce thrombin generation (19) (Table). It is generally assumed that heparin-induced thrombocytopenia can be avoided by limiting heparin use to fewer than 4 days (20). However, 8 of our patients received heparin for only 3 or fewer days. Thus, even if heparin use is restricted, at least a few patients will develop delayed-onset heparin-induced thrombocytopenia with

A prospective study to identify the risk factors associated with acute reactions to platelet and red cell transfusions

It is generally assumed that febrile nonhemolytic transfusion reactions are an immunologically mediated reaction involving the recipients plasma and the white cells in the donor unit. This has led to the use of white cell reduction and pretransfusion medication, to try to minimize these reactions. To better understand febrile transfusion reactions, a prospective study was performed in which all patients receiving platelet and red cell transfusions in a tertiary‐care medical center were interviewed before and after transfusion to obtain information about the typical presentation of the syndrome. It was found that transfusion reactions were much more frequently associated with platelet transfusion (30.8%) than with red cell transfusion (6.8%, p < 0.0005). The routine use of antipyretics prevented most episodes of fever but did not prevent the occurrence of other symptoms such as chills, cold, and discomfort. The application of logistic regression analysis revealed that the dominant factor determining the risk of a reaction was not white cell contamination, but the age of the component (p < 0.005). The significant relationship between reaction and the increasing age of the component suggests that cytokines released in the component during storage may be responsible for many reactions to blood components.