Diagnosis Of Heparin-induced Thrombocytopenia Type Research Articles

Multicentric validation of a rapid assay for heparin-induced thrombocytopenia with different specimen types

The diagnosis of heparin-induced thrombocytopenia type 2 (HIT) requires a combination of clinical and laboratory data. Rapid exclusion of HIT is supported by sensitive immunoassays. Citrated plasma or whole blood are more often available in the laboratory, and may thus, have practical advantages as compared to serum. In this study, various specimens from patients with suspected HIT were compared using a rapid lateral flow immunoassay (LFI-HIT). Serum, citrated whole blood and plasma were obtained from patients in whom HIT was suspected (n = 211) and were tested with LFI-HIT and several other assays. The comparison of plasma vs. serum in 210 samples showed agreement of 93.6% and between whole blood and serum in 183 samples was 96.7%. All serum-positive cases were correctly detected in plasma. Comparison of samples, which were positive in one of the immunoassays with the functional test heparin-induced platelet aggregation assay revealed a negative predictive value of 98.4% for serum, 97.8% for plasma and 96.2% for citrated whole blood. Performance in whole blood was slightly inferior. These data demonstrate that plasma and serum can be used in LFI-HIT with equivalent performance and that negative test results in LFI-HIT exclude HIT with high probability. The use of whole blood is not recommended by the authors.

Heparinom indukovana trombocitopenija tip II usled primene niskomolekularnog heparina kod dece

Heparin-induced thrombocytopenia (HIT) type II is a very rare complication of heparin use which is associated with high risk of developing life-threatening thrombosis. Clinical criteria for diagnosis of heparin-induced thrombocytopenia type II are: platelet ten days after the application of low-molecular-weight heparin for more than 50% of the initial number, the appearance of silent thrombosis, erythematous changes in the skin, normalization of platelet count within ten days after the exclusion of heparin, unproven other causes of thrombocytopenia, a positive finding of specific antibodies to the complex of heparin-TF4 based on agglutination test. The aim of this paper is to present a case of 12 years old girl with thrombocytopenia occurrence of type 2 after administration of anticoagulant therapy, low-molecular heparin (Fraxiparin ®) in the cubital vein thrombosis. In order to prevent occurrence of recurrent thrombosis and thromboembolic complications of anticoagulant therapy was administered nonheparin anticoagulants, direct thrombin inhibitor - danaparoid sodium. Due to the development of chemophagocytes syndrome, and to suppress the reaction between antibodies and heparin-TF4 complex, also were ordained an intravenous immunoglobulins. The measures applied leads to normalization of clinical status and laboratory parameters. In the case of heparin-induced thrombocytopenia type II, the use of heparin should be stopped and it is necessary to apply an alternative anticoagulant therapy to normalize platelet counts. Use of danaparoid has significant anticoagulant effect and leads to clinical improvements of heparin-induced thrombocytopenia type II.

Massive Right Atrial Thrombus Due to Heparin-Induced Thrombocytopenia Type II

2 weeks after elective coronary artery bypass grafting, a 61-year-old male patient was admitted to the intensive care unit with severe acute dyspnea. The initial postoperative clinical course had been uneventful, however, at postoperative day 6, the patient had suffered a right hemispheric transient ischemic attack. Thus, high-dose heparin therapy was started and activated partial thromboplastin time carefully monitored within therapeutic levels. Since paroxysmal atrial fibrillation was present, a thromboembolic event was initially suspected. Transesophageal echocardiography revealed small residues of a thrombus within the left atrial appendage (Figure 1). Interestingly, a highly mobile massive right atrial (RA) thrombus was detected (Figure 2) which was in agreement with the CT scan demonstrating multiple pulmonary embolisms of the right pulmonary artery. Laboratory analysis revealed novel thrombocytopenia (27 platelets/nl) as compared to a normal preoperative platelet count (198 platelets/nl). These findings were consistent with the diagnosis of heparin-induced thrombocytopenia type II (HIT II). Therefore, heparin was immediately discontinued and replaced by the direct thrombin inhibitor lepirudin. The suspected HIT II was confirmed by positive heparin-induced platelet aggregation (HIPA test). Within 36 h after the cessation of heparin, the platelet count recovered (91 platelets/nl) without any further thromboembolic events. Subsequent transthoracic echocardiography demonstrated increasing mobility of the massive RA thrombus partially prolapsing into the right ventricle (Figure 3) with threatening fatal occlusion of the right ventricular outflow tract. The patient was immediately transferred to cardiosurgery for successful removal of the massive round-shaped RA thrombus. In summary, HIT II caused thromboem1 Department of Medicine II, Cardiology, Asklepios Klinik St. Georg, Hamburg, Germany.

Laboratory diagnosis of heparin-induced thrombocytopenia type II after clearance of platelet factor 4/heparin complex

Laboratory confirmation of heparin-induced thrombocytopenia (HIT) is limited by assay sensitivity. We investigated whether laboratory confirmation can be improved after antigen clearance by determining free antibody and combining the results of antigenic and biologic assays. Blood samples were collected over 5 to 6 weeks in 14 HIT patients. As an antigenic assay, the fluorescence-linked immunofiltration assay (FLIFA) was performed, and as a biologic assay, the carbon 14–labeled serotonin release assay was performed. At day 1 when heparin was stopped, 11 of 14 patients showed positive results in both assays; thus each assay had a sensitivity of 80%. 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 to 100% at day 7, regardless of whether the antigenic or the biologic assay was performed first. Both assays became negative in all patients within 5 to 6 weeks. The sensitivity of antigen and biologic assays in HIT patients increased to 100% after the time course of the heparin-induced antibody. We assume that in some HIT patients the free antibody can be detected after withdrawal of heparin and after clearance of the platelet-factor 4/heparin complex. (J Lab Clin Med 2001;137:408-13)

This month in J Lab Clin Med: Issue highlights for June 2001

This month in J Lab Clin Med: Issue highlights for June 2001

Uncomplicated heparinization for cardiopulmonary bypass in a patient with antiheparin antibodies

THE SYNDROME of heparin-induced thrombocytopenia (HIT) is now recognized to consist of two distinct clinical entities.1-3 HIT type I is characterized by a mild thrombocytopenia (.100 3 109/L) usually occurring within 48 hours of initiating heparin, which is not associated with thrombotic or bleeding complications and which resolves spontaneously even with continued heparin administration. HIT type II is associated with a more profound thrombocytopenia (,100 3 109/L or ,50% of preheparin count) beginning 5 to 8 days after initiating heparin and follows a more malignant course. Patients with a diagnosis of HIT type II are at high risk for proximal vein or arterial thrombosis, pulmonary embolism, amputation, and death. HIT type I is believed to represent a direct aggregating effect of heparin resulting in increased clearance of platelets from the circulation. HIT type II is a result of antibody production to the complex formed by heparin and platelet factor 4 (PF 4). The pathogenic antibody is of the IgG class and can bind with Fc receptor sites on platelets and endothelial cells, resulting in activation and production of a prothrombotic state. Reaching a diagnosis of HIT type II has been assisted by the development of several laboratory assays for antiheparin antibodies. Although the assay techniques vary considerably, they can all be described generally as either physiologic or immunologic. The physiologic assays involve the detection of platelet activation when heparin is added to the patient’s serum. The 14C-serotonin release assay (SRA) is the archetypic physiologic assay and is considered the gold standard by many authors for the laboratory diagnosis of HIT type II. The cost, technical expertise, and requirement for radioactive materials, however, have limited the access to this test to large reference laboratories. The immunologic assays involve direct detection of antibodies in the patient’s serum to the heparin-PF 4 complex, most often by an enzyme-linked immunosorbent assay (ELISA). The commercial availability of an ELISA kit now provides wider access to serologic testing for HIT type II. Traditionally, a diagnosis of HIT type II was thought to be an absolute contraindication to heparin exposure. More recently, the safe conduct of cardiopulmonary bypass (CPB) with anticoagulation with single-dose heparin was reported for heart transplant patients with a diagnosis of HIT type II when antiheparin antibodies were no longer detectable by SRA.4 Although alternative anticoagulation techniques are available for CPB, the abandonment of well-established heparin protocols carries considerable risk and should be undertaken only when this approach clearly provides the safest course. A case is presented that shows the uncertainties in diagnosing HIT type II and the factors that must be considered before CPB.

Determination of heparin-induced IgG antibody in heparin-induced thrombocytopenia type II.

Heparin-induced thrombocytopenia is a relatively uncommon but severe side-effect of heparin therapy. Heparin-induced IgG antibody has been elucidated to be the main isotype and the most pathogenic antibody in the pathophysiology. As affected patients are at high risk of developing thrombotic events, confirmation of the clinical diagnosis and avoidance of heparin re-exposure are important and desirable. In the present study, heparin-induced IgG was measured by the binding of neoantigens, which were prepared by incubating FITC-heparin with platelet factor 4 present in normal serum. The cross-reactivities of heparin-induced IgG with low-molecular-weight heparin and danaparoid were analysed by competitive binding. A total of 81 clinically suspected heparin-induced thrombocytopenia type II patients were analysed. Thirty-seven of 38 heparin-induced thrombocytopenia type II patients, in whom thromboembolism was confirmed by objective methods, had elevated relative fluorescence intensity ratios (patient normal control) and 36 had positive heparin-induced platelet activation results. The prevalence of heparin-induced IgG in heparin-induced thrombocytopenia type II patients was 97.4%. Positive heparin-induced IgG results were: 0/319 healthy volunteers, 0/38 other thrombo-cytopenia and 2/56 heparin/low-molecular-weight heparin-receiving patients without thrombocytopenia, 2/41 hyperbilirubinaemic patients and 2/50 hyperlipidaemic patients. A small amount of cross-reaction assays showed similar results as obtained in heparin-induced platelet activation. Our results suggest that a very high frequency of heparin-induced IgG in heparin-induced thrombocytopenia type II patients can be detected using a novel antigen assay. The rapid determination of pathogenic heparin-induced IgG may be a useful tool for the rapid diagnosis of heparin-induced thrombocytopenia type II that could facilitate further management of the patients.

Heparin induced thrombocytopenia

Thrombocytopenia is a known adverse reaction occurring in some of the patients receiving heparin. Two types of heparin-induced thrombocytopenia (HIT) have been described. HIT type I is mild thrombocytopenia probably caused by a direct proaggregating effect of heparin and occurs during the first few days of heparin treatment. No specific treatment is necessary. HIT type II is a severe thrombocytopenia mediated by an immunologic mechanism where antibodies against heparin/platelet factor 4 (PF4) complexes play a major role. Thrombocytopenia usually commences 4-14 days after the onset of heparin administration. The incidence of HIT type II is below 3% and even lower when low-molecular weight heparin is used. The possible occurrence of life-threatening thrombembolic events may complicate the course of HIT type II. Diagnosis of HIT type II by clinical features alone is often difficult. A few laboratory tests are pertinent for diagnosing HIT type II including the 14C-serotonin assay, the heparin-induced platelet activation test and the heparin/PF4 ELISA. Immediate cessation of heparin administration is essential in the treatment of patients with HIT type II, if need be even without waiting for the result of the antibody search test. Several alternatives of anticoagulation for patients with HIT type II have been investigated in the past. Danaparoid-sodium as well as recombinant hirudin have shown promising results when used for this purpose.