Heparin induced thrombocytopenia. Variable platelet-rich plasma reactivity to heparin dependent platelet aggregating factor

The heparin dependent platelet aggregating factor in the serum from an individual with heparin induced thrombocytopenia exhibited reactivity with only 50% of an extensive panel of normal platelet rich plasmas, and this variability was independent of the platelet rich plasma platelet Factor 4 content. Individual sera of 3 other patients with heparin induced thrombocytopenia showed considerable variation in the lag phase and rate of platelet aggregation when tested with different normal platelet rich plasma preparations. These findings suggest that in the appropriate clinical setting the documentation of heparin dependent platelet aggregating factor should employ a panel of platelet rich plasmas if the initial screen is negative.     

Heparin-induced thrombocytopenia (HIT): pathogenesis, laboratory test, and treatment

Heparin-induced thrombocytopenia(HIT) due to immunological mechanisms is known as an important adverse reaction to heparin treatment, and heparin treatment should be applied while keeping in mind the risk of onset of HIT 5-14 days after the initiation of heparin. The presence of HIT had not been fully recognized in clinical practice in Japan despite the management of HIT being well confirmed in Western countries. Recognition of HIT has increased since argatroban, a direct thrombin inhibitor, obtained the approval of the FDA for prevention and treatment of HIT. Although the incidence of HIT in Japan has not yet been clarified, there is some evidence that HIT is encountered in critically ill patients undergoing heparin anticoagulation. Clinical diagnosis of HIT is performed by means of thrombocytopenia of a drop of 50% or 100 x 10(30/microl for 5 -14 days after starting heparin treatment. Confirmatory laboratory tests examine whether the patients have antibodies against heparin/PF4 complexes or not. Two assay tests for detecting heparin/PF4 complex antibodies are available in Japan. As a functional test, the heparin-induced platelet aggregation method is easily performed and the result is obtained in a short time. The result of the test has, however, been misleading due to the selection of donors. Low platelet activity of the donors on the addition of heparin induces a negative response in spite of positive antibodies in the sample. Before testing samples, it is important to check heparin reactivity of the donor's platelets. Enzyme immunoassay detecting the antibodies is available as a commercial kit. Sensitivity obtained by enzyme immunoassay is very high and often introduces false-positives. Careful attention to interpretation of the result is required. Treatment of HIT should be started at the time of recognition of thrombocytopenia while antibody testing for HIT is performed. As an alternative anticoagulant to heparin, argatroban should immediately be applied to avoid complication of thrombosis. Thrombocytopenia and hypercoagulability quickly recover to the preheparin level by the appropriate use of argatroban.     

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 thrombocytopenia. In the remaining 73 patients (30 percent), the onset of thrombocytopenia was rapid (median time of onset, 10.5 hours after the start of heparin administration); all these patients had been treated with heparin within the previous 100 days. During recovery from thrombocytopenia, heparin-dependent antibodies in the serum fell to undetectable levels at a median of 50 to 85 days, depending on the assay performed. In the seven patients who were given heparin again after the disappearance of heparin-dependent antibodies, a new episode of heparin-induced thrombocytopenia did not occur. CONCLUSIONS: Heparin-induced thrombocytopenia can begin rapidly in patients who have received heparin within the previous 100 days. Heparin-dependent antibodies do not invariably reappear with subsequent heparin use.     

Changes in platelet aggregation during cardiopulmonary bypass: comparison of poly-2-methoxyethylacrylate and heparin as a circuit coating material

At present, there are various biomaterials that have high biocompatibility. In particular, there are many types of coated circuits in cardiopulmonary bypass (CPB) systems. However, only a few clinical studies have investigated platelet aggregation caused by these coated circuits. In this study, a CPB system coated with poly-2-methoxyethylacrylate (X coating) was used to ascertain whether platelet aggregation could be suppressed during CPB, and a comparison was made between X coating and ordinary (covalently bonded) heparin coating. The subjects were 19 adult patients who were scheduled to undergo valve replacement or valvuloplasty. They were divided into two groups: group X (X coating) and group H (heparin coating). The platelet aggregation threshold index (PATI, grading curve) and β-thromboglobulin and plalelet factor IV levels were assessed preoperatively (control), 5 min after heparin administration, 10 and 60 min after the start of CPB, and 0 and 2 h after the end of CPB. The results indicated that platelet aggregation was reduced during CPB and that platelets were activated. The changes in platelet aggregation associated with the X coating were shown to be similar to those associated with heparin coating.     

Pathomorphological aspects of heparin-induced thrombocytopenia II (HIT-II syndrome)

The therapeutic use of heparin results in thrombocytopenia in 5–30% of patients. In 0.1–1% of patients treated with heparin, the platelet count decreases to between 100 × 10⁹/l and 50 × 10⁹/l and leads to severe synchronous central arterial and venous thrombosis with a mortality of 18–36%. This is known as ”white-clot syndrome” or heparin-induced thrombocytopenia II (HIT-II syndrome). Whilst the clinical aspects and the central type of thrombosis in HIT-II syndrome are well documented, the histomorphology and differential diagnosis of thrombosis are not. We report three cases of HIT-II syndrome with thrombosis of the central arteries and veins. The HIT-II thrombi could be differentiated from thrombi of other origins, particularly from mural thrombi. Heparin-induced thrombi were seen on microscopical examination to be like onion skin in structure, and immunohistochemistry showed that they had a markedly reduced content of fibrin and clearly enhanced amounts of IgG and IgM. The layered structure thus implied appositional growth. The thrombi in HIT-II syndrome do not seem to be induced by activation of the coagulation cascade, but by platelet aggregation mediated by anti-platelet antibodies.     

Heparin-associated thrombocytopenia in maintenance hemodialysis patients

Thrombocytopenia associated with the presence of a heparin-dependent platelet aggregating factor developed in two patients after hemodialysis with heparin. It resolved in one patient after heparin was stopped; but persisted in the other during a two-week heparin-free period and intermittently thereafter. We suggest that when heparin causes thrombocytopenia in dialysis patients the heparin should be stopped whenever possible, but this may not be necessary in all patients.     

Heparin induced platelet aggregation: in vitro confirmation of thrombotic complications associated with heparin therapy

Eleven patients who developed thromboembolic complications while receiving heparin were studied for a possible adverse reaction to heparin as the cause of their progressive thrombosis. Fifteen additional patients who were receiving heparin for recurrent thromboembolism, but who did not develop signs of thrombotic complications, were studied as patient controls. The most significant finding was an abnormal in vitro aggregation response to heparin alone in all of the patients who developed complications who were tested for it (64 percent). None of the patient controls demonstrated this abnormality. In addition, thrombocytopenia was noted in all of the former but in only one of the latter. Results of prothrombin times, fibrinogens and fibrin split products eliminated disseminated intravascular coagulation as the cause of the thrombocytopenia in the majority of cases. Finally, an approach to the early detection of the abnormal heparin response is presented and guidelines for its therapeutic management are recommended.     

Improved laboratory confirmation of heparin-induced thrombocytopenia type II. Time course of antibodies and combination of antigen and biologic assays

We studied whether laboratory confirmation of heparin-induced thrombocytopenia (HIT) can be improved after antigen clearance by determining free antibody and combining the results of an antigenic and a biologic assay. Blood samples taken over 40 days in 14 patients with HIT with thromboembolism underwent fluorescence-linked immunofiltration and the carbon 14-serotonin release assays. Of the 14 patients, 11 showed positive results in both assays at day 1 after stopping heparin. The 3 patients with negative results seroconverted in one or both assays during the subsequent 7 days. Combining the positive results of the assays increased the sensitivity from 85% at day 1 to 100% at day 7. Assay results became negative in all patients within 40 days. The platelet count normalized between days 2 and 9 after withdrawal of heparin. It is assumed that the free antibody can be detected after withdrawal of heparin and after clearance of the platelet factor 4-heparin complex in patients with HIT.     

Coronary thrombosis in a patient with May-Hegglin anomaly.

May-Hegglin anomaly (MHA) is a rare hereditary condition that is characterized by cytoplasmic inclusions in leukocytes and giant platelets. Many patients have some degree of thrombocytopenia. Most individuals with MHA are asymptomatic, but 25-43% of patients previously reported have had a hemorrhagic tendency. The authors describe a patient with MHA who had no history of hemorrhage but who developed complete coronary thrombosis after attempted angioplasty despite an apparent platelet count of 24,000 per mm3. Laboratory investigations revealed a normal bleeding time, normal platelet aggregation, and an increase in the size of approximately two-thirds of the platelets. The calculated platelet mass was near normal, which probably explains the thrombosis despite a decrease in platelet numbers. The authors conclude that in some patients with MHA platelets are functionally active both in vivo and in vitro.     

Use of theophylline in the investigation of pseudothrombocytopenia induced by edetic acid (EDTA-2K).

In automated cell counting of edetic acid (EDTA-2K) anticoagulated blood, thrombocytopenia is occasionally seen which bears no relation to any underlying disease. In this study a heparin and soluble theophylline mixture was used to measure accurately platelet numbers in patients with such pseudothrombocytopenia. In four normal volunteers, a theophylline concentration of more than 7 mg/ml produced no significant difference in platelet numbers between theophylline and heparin and EDTA-2K anticoagulated bloods. When blood treated with EDTA-2K was used in seven patients with pseudothrombocytopenia, falsely low platelet counts were observed in three patients immediately after sampling; in blood treated with theophylline, white cell and platelet counts remained unchanged for up to six hours after sampling. Microscopical examination of the EDTA-2K anticoagulated blood showed massive platelet clumping, but no aggregates were seen in theophylline anticoagulated blood. It is concluded that theophylline can be useful in the investigation of pseudothrombocytopenia when an automated cell counter is used.     

Pituitary Metastasis Presenting as Ischemic Pituitary Apoplexy Following Heparin-induced Thrombocytopenia

Pituitary apoplexy (PA) typically results from infarction or hemorrhage in a pituitary adenoma, while PA in nonadenomatous pituitary gland is uncommon. Prothrombotic states have never been recognized as precipitating factors for PA. The authors report a case of an elderly female who received prophylactic fractionated heparin therapy due to sepsis, consequent rhabdomyolysis, and overt disseminated intravascular coagulation. On the seventh day of heparin therapy, she reported sudden vision loss, ptosis, diplopia, and severe headache. Severe thrombocytopenia and positive antibodies to the complex of platelet factor 4 and heparin confirmed heparin-induced thrombocytopenia type 2 (HIT). Magnetic resonance imaging disclosed a homogenous pituitary tumor mass with pronounced sphenoid sinus mucosa thickening and two hypointense zones within the tumor mass on contrast-enhanced images consistent with focal ischemic necrosis. The tumor was confirmed to be squamous cell carcinoma with no signs of necrosis. Ischemic necrosis was found within marginal pituitary tissue. This is the first reported case of ischemic PA associated with pituitary metastasis and the first case in which HIT triggered PA. Our case demonstrates that prothrombotic states such as HIT can precipitate ischemic PA. Pituitary metastasis can present with ischemic PA, but radiological features differ from those described in pituitary adenomas. Segregated low-signal intensity zones within the tumor mass on postcontrast images indicate partial infarction of the tumor, which could be a special feature of ischemic PA in pituitary metastasis and has never been described in pituitary adenomas. These are all novel findings and might enlighten the pathogenesis of PA.     

Successful treatment of refractory thrombocytopenia with mycophenolate mofetil in a patient with systemic lupus erythematosus

While mild thrombocytopenia in systemic lupus erythematosus (SLE) is frequently seen in the context of active disease, severe thrombocytopenia causing significant bleeding is not that common. Corticosteroids are considered the first line therapy for severe thrombocytopenia in SLE. Second-line therapeutic agents or splenectomy have been reported to be effective for patients who fail to respond to steroids or those who require moderate doses of steroids to maintain the platelet counts. Recent randomized controlled studies have shown that mycophenolate mofetil (MMF) is an efficacious and safe therapeutic agent in patients with proliferative forms of lupus nephritis. However, little information has been available regarding the role of MMF in the treatment of immune thrombocytopenia complicated with SLE. Hereby I describe a patient with SLE in whom thrombocytopenia was refractory to corticosteroids, intermittent intravenous cyclophosphamide, azathioprine, cyclosporine, intravenous gamma globulin, danazol, and splenectomy, and whose platelet counts eventually normalized during therapy with MMF. In this patient, thrombocytopenia is initially thought to be associated with active SLE involving major organ. However, after immunosuppressive agents were given, the refractory nature of thrombocytopenia seems to be an isolated phenomenon, independently of SLE activity.     

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.     

Trombocytopenia: one of the markers of disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is a complication of a variety of severe underlying diseases and a contributing factor in multi-organ failure and death. DIC is diagnosed on the basis of clinical findings (organ failure, bleeding) and laboratory abnormalities. The laboratory data include (repeated) measurements of platelet count and global clotting tests, to which more specific and sensitive tests for activated coagulation are added. The focus of this paper is on thrombocytopenia (platelet count < 100 x 103/microl) as a marker in DIC. First, in patients with suspected DIC it is imperative to consider alternative causes of thrombocytopenia,such as related to heparin use (heparin induced thrombocytopenia II) or thrombocytopenic purpura. Second, the observation of thrombocytopenia in relation to DIC should be interpreted as a marker of advanced or overt DIC and not as an early indicator.According to recommended guidelines measurements of platelet counts should always be coupled to a panel of coagulation markers and not be used as single marker of DIC (or other syndromes). In general, thrombocytopenia should not trigger platelet transfusions except in patients with severe bleeding complications.     

Heparin-induced thrombocytopenia: laboratory investigation and confirmation of diagnosis.

We report here on the usefulness of the 14C-serotonin release assay for the laboratory confirmation of the clinical diagnosis of heparin-induced thrombocytopenia syndrome (HITS). Over the past 3 yrs, some 140 individual serum samples have been tested in our laboratory for heparin-associated anti-platelet activity ('heparin antibodies'). These included sera from 54 selected (4 positive, 50 negative) controls and a group of 86 patients where the test was requested on clinical grounds. Of 20 patients derived from within our institution, 7 out of 8 patients (88%) with good clinical probability of HITS were confirmed to have heparin platelet antibodies by the serotonin release assay. In contrast, only 2 out of 9 patients (22%) with a low clinical probability of HITS were shown to be positive by this procedure, as were 2 out of 3 patients (66%) deemed to have an 'intermediate' clinical probability of HITS. In addition, screening of 50 serum samples forming a 'negative-control non-HITS' group (either patients on heparin therapy without thrombocytopenia, patients with non-heparin associated thrombocytopenia [eg. ITP*, other drug related], or normal laboratory volunteers), consistently failed to display heparin associated anti-platelet activity by the 14C-serotonin release assay. In addition to the good specificity and sensitivity described above, the 14C-serotonin release assay was found to be nearly twice as sensitive when compared to the platelet aggregation procedure, and it is therefore a useful diagnostic test for the confirmation of clinically suspected HITS.     

Heparin-induced thrombocytopenia with multiple organized thrombi accompanied by unusual cholesterin deposition: Autopsy case after long-term follow up

Heparin-induced thrombocytopenia (HIT) is characterized by a reduction in the platelet count and systemic thromboembolism during heparin therapy. Herein is reported a case of HIT with characteristic thrombus formation. A 68-year-old man who had been treated for hypertension for 27 years suffered a brain infarction and was treated with heparin. After this treatment, other new infarctions occurred in multiple organs. Because serum antibodies against heparin/PF4 complex were detected, he was diagnosed as having HIT, and warfarin and argatroban were administered instead of heparin. He died, however, 119 days after the first onset. At autopsy infarction due to organized thrombi with cholesterin deposition in multiple organs were found, similar to usual atherosclerotic emboli, but different to them with regard to clinical course and distribution of thrombi. This case in which organization and frequent cholesterin deposition were found in thromboembolized lesions of multiple organs after relatively long-term follow up, is unusual. The findings suggest that HIT accompanied by marked hypercholesterolemia of long duration contributes to a characteristic form of thromboembolism that needs careful management.     

Isoimmune neonatal thrombocytopenia: a case report and review

Isoimmune neonatal thrombocytopenia is an unusual problem with significant morbidity and mortality. Though it is often self-limited, it is potentially fatal due to hemorrhage. Specific therapy with compatible platelets is indicated. In previously unrecognized cases, platelet antigen and antibody studies delay therapy unacceptably. Therefore, maternal platelets are used, which also aid in establishing a therapeutic diagnosis. A case of isoimmune neonatal thrombocytopenia is reported, and the etiology, clinical and laboratory implications, and methods of management are discussed.     

Inherited platelet disorders : Management of the bleeding risk

Inherited platelet disorders are rare bleeding syndromes due to either platelet function abnormalities or thrombocytopenia which may be associated with functional defects. The haemorrhagic symptoms observed in these patients are mostly muco-cutaneous and of highly variable severity. Although 30 to 50% of the platelet disorders are still of unknown origin, the precise diagnosis of these pathologies by specialized laboratories together with haemorrhagic scores enables an assessment of the risk of bleeding in each patient. Depending on the diagnostic elements collected, an appropriate medical procedure can be proposed for each situation: scheduled or emergency surgical interventions and pregnancy follow-up. The pathologies most at risk correspond to Glanzmann's thrombasthenia, Bernard-Soulier syndrome, severe thrombocytopenia (< 40,000 platelets/μL) and signalling protein abnormalities affecting the activation of GPIIb-IIIa, a membrane glycoprotein essential for platelet aggregation. For these particular patients, in whom the risk of bleeding can be increased by a factor of 40, management protocols during surgical procedures are generally based on the use of conventional platelet concentrates, for both prophylaxis and the control of active bleeding. The perinatal period in women with platelet disorders and their new-born also require special attention. Indeed, beyond unpredictable delivery haemorrhages, bleeding requiring a blood transfusion is observed after delivery in more than 50% of women with Glanzmann's thrombastenia or Bernard-Soulier syndrome.     

Lepirudin

Lepirudin is a recombinant hirudin derived from transfected yeast cells. The hirudins are direct thrombin inhibitors which render the thrombin molecule incapable of promoting fibrin formation and catalysing other haemostatic reactions. In initial studies, parenteral lepirudin has shown promising efficacy as an antithrombotic agent. Lepirudin increased or maintained platelet counts at normal baseline values while maintaining adequate anticoagulation in patients with heparin-induced thrombocytopenia (HIT), and has not been associated with the development of immune-mediated thrombocytopenia. Preliminary studies in patients with deep vein thrombosis (DVT) suggest that lepirudin may be more effective than unfractionated heparin (UFH) at preventing pulmonary perfusion defects. In patients with unstable angina pectoris, preliminary data also showed lepirudin to be significantly more effective than UFH according to the combined incidence of cardiovascular mortality, new acute myocardial infarction (AMI) or refractory angina. However, additional studies involving larger patient numbers are necessary before firm conclusions can be made regarding the relative efficacy of lepirudin in these indications. Similarly, promising but limited data on the use of lepirudin during haemodialysis or heart surgery and in patients with disseminated intravascular coagulation (DIC) require further confirmation. Bleeding complications and the possible induction of allergic or anaphylactic reactions are the most serious adverse events associated with lepirudin therapy. Major bleeding complication rates appear to be similar with lepirudin and UFH monotherapy; however, lepirudin may be associated with an increased incidence of minor bleeding including bruising. Initial encouraging results showing an improvement in coronary artery patency with high-dose lepirudin versus UFH as an adjunct to thrombolytic therapy in patients with AMI were subsequently overshadowed by reports of a high incidence of major bleeding events including cerebral haemorrhage among lepirudin recipients. Moreover, at lower doses which did not produce an unacceptably high incidence of haemorrhagic complications, lepirudin appeared to have only a small efficacy advantage over UFH. CONCLUSIONS: Lepirudin has shown promising activity as an antithrombotic agent and may be a suitable substitute anticoagulant for heparin in patients with HIT. The narrow therapeutic window of lepirudin makes it difficult to assess the role of this agent when used as an adjunct to thrombolytic therapy in patients with AMI. However, initial data suggest that lepirudin may be a potentially useful agent in the management of patients with unstable angina, DVT or DIC and in preventing thrombus formation in extracorporeal circuits. Further studies should more fully elucidate the efficacy of lepirudin in these indications.