Evaluation of the use of a heparin dose-response test in dogs to determine the optimal heparin dose during intravascular procedures and assessment of the in vitro heparin response in healthy dogs.

BACKGROUND: No guidelines for administering and monitoring anticoagulants intraprocedurally are currently available in dogs, despite the prevalence of procedures necessitating systemic anticoagulation with heparin. OBJECTIVES: To evaluate an activated clotting time (ACT)-based heparin dose-response (HDR) test to predict the individual required heparin dose in dogs during intravascular procedures, and to investigate both the in vitro heparin - ACT and in vitro heparin - factor anti-Xa activity (anti-Xa) relationships in dogs. METHODS: Blood was collected from eight healthy beagles undergoing a cardiac procedure and utilised to establish baseline ACT and for in vitro evaluation. Subsequently, 100 IU/kg heparin was administered intravenously (IV) and ACT was remeasured (HDR test). The required heparin dose for an ACT target response ≥300 s was calculated for each individual and ACT was remeasured after administration of this dose. For in vitro testing, a serial heparin blood dilution (0-0.5-1-2-4 international unit (IU)/mL) was prepared and ACT and anti-Xa were determined using whole blood and frozen plasma, respectively. RESULTS: The HDR test overestimated the required heparin dose in 3/7 dogs. In vitro, ACT and anti-Xa increased significantly with increasing blood heparin concentration. Heparin - ACT was nonlinear in 4/8 dogs at heparin concentrations >2 IU/mL, whereas heparin - anti-Xa remained linear throughout the tested range. CONCLUSIONS: The HDR test poorly estimated the required heparin dose in dogs. This is most likely attributed to a nonlinear heparin - ACT relationship, as observed in vitro. Anti-Xa is a promising alternative for ACT; however, unavailability as a point-of-care test and lack of in vivo target values restrict its current use.

Identification of high thrombotic risk triple-positive antiphospholipid syndrome patients is dependent on anti-cardiolipin and anti-ß2glycoprotein I antibody detection assays.

Essentials Triple-positivity is associated with a high risk for a first thrombotic event and recurrence. Identification of triple-positives is dependent on the solid phase assay used. In triple-positivity, IgM only adds value in thrombotic risk stratification together with IgG. Thrombotic risk in triple-positive patients with IgM only, depends on the platform. ABSTRACT: Background The antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity with the persistent presence of antiphospholipid antibodies (aPL). Triple-positivity (i.e. positivity for lupus anticoagulant [LAC], anti-cardiolipin [aCL] and anti-ß2glycoprotein I [aß2GPI] antibodies) is associated with a high thrombotic risk. Objectives We investigated the variability in triple-positivity detection by measuring the same samples with four commercially available solid phase assays. In addition, the added clinical value of aPL in LAC-positive patients was investigated, as well as the association of IgM triple-positivity and thrombosis. Patients/Methods We included 851 patients from seven European medical centers. Anti-CL and aß2GPI IgG/IgM antibodies were determined by four platforms: BioPlex® 2200, ImmunoCap® EliA, ACL AcuStar® and QUANTA Lite ELISA® . Results Triple-positivity detection by solid phase assays varied, ranging from 89 up to 118 in thrombotic APS patients (n = 258), of which 86 were detected independent of the platform. Lupus anticoagulant positivity resulted in an odds ratio (OR) for thrombosis of 3.4; triple-positivity (irrespective of the isotype) increased the OR from 4.3 up to 5.2, dependent on the platform. Triple-positivity solely for the IgM isotype did not increase the OR for thrombosis compared with LAC positivity. The highest OR for thrombosis was reached for positivity for IgG and IgM aß2GPI and aCL (8.6 up to 28.9). Conclusions Triple-positivity proved to be highly associated with thrombosis, but identification is assay dependent. Within triple-positivity, IgM antibodies only have an added clinical value in patients positive for IgG antibodies.

Pre-analytical stability of coagulation parameters in plasma stored at room temperature.

INTRODUCTION: Haemostasis testing is influenced by many pre-analytical variables, such as storage time and temperature, which can affect the stability of coagulation factors and influence the results of coagulation assays. We investigated the stability of haemostasis tests after storage of aliquoted plasma at RT, including the variability of measurement principle and reagent used for determination. METHODS: Blood samples from 20 healthy volunteers were obtained, processed to PPP and aliquoted. Aliquots were stored at RT for 0 hour, 2 hours, 4 hours, 6 hours, 8 hours, 12 hours, 24 hours and 48 hours. PT, aPTT, fibrinogen, D-Dimers and coagulation factors (FII, FV, FVII, FX, FVIII, FIX, FXI, FXII) were determined by STA-R Max® and ACL-TOP® . VWF:Ag and vWF:RCo were determined by AcuStar® . Clinically relevant changes, compared to the initial measurement, were denoted as a percentage change of > 10% according to the 99% CI. RESULTS: For both analysers, a clinically relevant change of > 10% was observed for FV after 2 hours, FVIII after 4 hours and for aPTT, FII, FVII, FX and FXII after 48 hours of storage at RT. Statistically significant, but no clinically relevant differences were observed after 48-hours storage for PT, fibrinogen and FIX. D-Dimers, FXI, vWF:Ag and vWF:RCo were found stable up to 48 hours at RT. CONCLUSION: Overall, compared to the limits given by the current CLSI guidelines, for most coagulation parameters investigated in this study a longer storage period could be accepted. Time intervals for FVIII and FV dosage were shorter than recommended by the CLSI guidelines. For PT determination, our findings were consistent.

Role of anti-domain 1-ß2 glycoprotein I antibodies in the diagnosis and risk stratification of antiphospholipid syndrome.

UNLABELLED: Essentials Antibodies to domain 1 of ß2 glycoprotein I (aD1) are a subset of antiphospholipid antibodies. We evaluated the added diagnostic value of an automated aD1 assay in antiphospholipid syndrome. AD1 IgG correctly classifies patients at risk for thrombosis. Agreement between aD1 and aß2GPI IgG is high, limiting the added value of aD1 in our setting. Click to hear Professor de Groot's perspective on new mechanistic understanding in antiphospholipid syndrome SUMMARY: Background Laboratory diagnosis of antiphospholipid syndrome (APS) includes lupus anticoagulant (LAC), anticardiolipin (aCL) or anti-ß2 glycoprotein I (aß2 GPI) antibodies. Antibodies targeting domain 1 of ß2 GPI (aD1) constitute a pathogenic subset of autoantibodies. Objectives In this cohort study, we determined the clinical performance characteristics, additional diagnostic value and the contribution to APS risk stratification of an automated aD1 assay. Patients/Methods LAC, aCL, aß2 GPI and aD1 IgG were measured in 101 APS patients, 123 patients with autoimmune disorders, 82 diseased controls and 120 healthy controls. aD1 antibodies were detected by QUANTA Flash(®) Beta2GPI-Domain 1 chemiluminescence immunoassay. Results With a cut-off value of 20.0 CU, the aD1 IgG assay identifies APS patients in a clinically affected patient cohort with a sensitivity of 53.5% and specificity of 98.8%. It implied a high odds ratio (OR) for clinical events (OR, 17.0; 95% confidence interval [CI], 7.1-40.5). aD1 IgG did not add diagnostic value to the formal aPL panel because aß2 GPI IgG was nearly as specific but more sensitive for APS (sensitivity 56.4%) with a higher OR for clinical events (36.2; 95% CI, 11.1-117.9). High aD1 titers identify triple-positive patients and patients with thrombosis in a ß2 GPI-dependent LAC-positive population. Agreement between aD1 IgG and aß2 GPI IgG was high (positive and negative agreement 91.7% and 98.4%, respectively). Conclusion Detection of aD1 IgG correctly classifies patients at risk of thrombosis. However, the contribution of aD1 IgG to APS diagnosis and risk stratification depends upon the solid phase assays used for aCL and aß2 GPI detection.

Mixing studies in lupus anticoagulant testing are required at least in some type of samples.

BACKGROUND: According to the ISTH guidelines for lupus anticoagulant (LAC) testing, the second step in the three-step procedure (screening, mixing, and confirmation) is the mixing test, which improves the discrimination between the presence of an inhibitor and coagulation factor deficiencies such as those occurring in patients receiving vitamin K antagonists (VKAs). OBJECTIVES: From a retrospective analysis of dilute Russell viper venom (dRVVT) results, we evaluated the impact of the mixing test result on the interpretation of LAC positivity. METHODS: We interpreted the dRVVT clotting times with and without taking into account the results of the mixing test in a patient population with prolonged screening test (n = 267) with special attention to the patients receiving VKAs. RESULTS AND CONCLUSIONS: The number of samples classified as 'LAC positive' differed substantially depending on the method of interpretation; 170 and 235 of 267 samples were classified as LAC positive with the three- and two-step procedure, respectively. Discrepancy between the two-step (without mixing step) and the three-step procedure was due to not including a mixing test and was more pronounced in the VKA patient population. Screen/confirm ratios carried out on a 1:1 mix of patient and normal pooled plasma (NPP) gave a lower incidence of 59 of 267. We advise continuing to perform mixing test to avoid false-positives. In patients with discrepant results between the two- and three-step dRVVT interpretation, mainly observed in VKA-treated patients, we advise retesting of the patients preferable beyond the period of anticoagulant therapy and additional testing for anti-beta2GPI and/or anti-cardiolipin antibodies.

Lupus anticoagulant-hypoprothrombinemia syndrome: report of two cases and review of the literature.

Lupus anticoagulant-hypoprothrombinemia syndrome (LA-HPS) is a rare acquired disorder caused by prothrombin antibodies. The disease is most common in the pediatric age group (<16 years), and more prevalent in women. There are well-established clinical diseases associated with LA-HPS, most notably systemic lupus erythematosus (SLE) and viral infections. The clinical manifestation of LA-HPS varies greatly in severity and it may cause severe life-threatening bleeding diathesis. LA-HPS is to be suspected when a patient presents with bleeding and a prolonged activated partial thromboplastin and prothrombin time, in combination with a lupus anticoagulant. The diagnosis is confirmed in the laboratory by identification of reduced prothrombin levels. There are no standardized recommendations for treatment of the hemorrhage associated with the syndrome; corticosteroids are used as first-line treatment. This review summarizes what is currently known about the pathogenesis, clinical features, diagnosis, treatment and prognosis of LA-HPS, and presents two case reports.

Antiphospholipid antibody testing and standardization.

The laboratory criteria that define patients with antiphospholipid syndrome (APS) include lupus anticoagulant (LAC), anticardiolipin antibodies and anti-ß2 glycoprotein I antibodies (aß2GPI). All assays show methodological shortcomings and the combination of the three tests, each with different sensitivity and specificity, and hence, differences in clinical utility make the laboratory diagnosis of APS challenging. Consensus guidelines and proposals for antiphospholipid antibodies (aPL) testing have been published in the last 20 years and have led to a substantial improvement. Despite efforts so far, standardization is not reached yet, but progress has been made. On-going efforts to reduce the interlaboratory/interassay variations remain important; even an absolute standardization cannot be feasibly achieved. Taking into account the methodological shortcomings of the means we have available, more detailed guidelines may help in adequate performance of aPL testing. This review will focus on the efforts and achievements in standardization and on the weaknesses and strengths of the current available laboratory methods.

Acquired hemophilia: a case report and review of the literature.

Acquired hemophilia A (AHA) is a rare bleeding disorder caused by autoantibodies against clotting factor VIII (FVIII). FVIII autoantibody is characterized as polyclonal immunoglobulin G directed against the FVIII procoagulant activity. This disease occurs most commonly in the elderly population and with preponderance of men in nonpregnancy-related AHA. There are well-established clinical associations with AHA such as malignancy, other autoimmune diseases and pregnancy. However, up to 50% of reported cases remain idiopathic. The clinical manifestation of AHA includes mostly spontaneous hemorrhages into skin, muscles and soft tissues, or mucous membranes. AHA should be suspected when a patient with no previous history of bleeding presents with bleeding and an unexplained prolonged activated partial thromboplastin time. The diagnosis is confirmed in the laboratory by the subsequent identification of reduced FVIII levels and FVIII inhibitor titration. There is a high mortality, making prompt diagnosis and treatment vitally important. The principles of treatment consist in controlling the bleeding and eradicating the inhibitor. Because of the overall high relapse rate (15-33%), it is also recommended to follow up these patients. The review summarizes what is currently known about the epidemiology, pathogenesis, clinical features, diagnosis, treatment and prognosis of AHA and starts with a case report.

Validation of a new panel of automated chemiluminescence assays for von Willebrand factor antigen and activity in the screening for von Willebrand disease.

INTRODUCTION: The diagnosis of von Willebrand disease (VWD) largely depends on the results of von Willebrand factor (VWF) antigen and activity. Recently, a new automated VWF:RCo assay on Acustar was developed. This assay panel for VWD also contains a new antigen (VWF:Ag) test. In this study, both chemiluminescence tests (HemosIL VWF:Ag and VWF:RCo) were evaluated. MATERIALS AND METHODS: Imprecision, limit of detection (LOD), and linearity were evaluated. Method comparison (with VWF:Ag latex assay and VWF:RCo by aggregometry) was performed and diagnostic performance of the new test panel was examined. RESULTS: The imprecision was 7%, and the LOD was 0.2 IU/dL for both assays. Dilution series showed a large linearity for both HemosIL VWF:Ag (0-300 IU/dL) and VWF:RCo (0-200 IU/dL) and method comparison studies revealed good agreement with the currently used VWD panel. The new panel showed adequate diagnostic performance: diagnostic sensitivity was 100% and diagnostic specificity 82% compared with the VWF:Ag latex assay and VWF:RCo by aggregometry. In addition, the new HemosIL Acustar VWF:Ag and HemosIL Acustar VWF:RCo are more sensitive for VWD than the currently used assays. CONCLUSIONS: This new VWD test panel has adequate laboratory characteristics and allows fully automated and simultaneous analysis of the VWF:Ag and VWF:RCo.

Standardization of antiphospholipid antibody assays. Where do we stand?

The laboratory criteria (lupus anticoagulants (LA), and/or anti-cardiolipin (aCL) antibodies and/or anti-ß2-glycoprotein I antibodies (aß2GPI)) that define patients with antiphospholipid syndrome (APS) were set in the Sapporo and Sydney criteria published in 1999 and 2006, respectively, and led to a substantial improvement in the recognition of APS. In addition, guidelines for LA detection were published by the Scientific Standardisation Subcommittee (SSC) of the International Society of Thrombosis and Haemostasis (ISTH) in 2009. However, a number of questions on this respect remain unresolved. Recommendations for the aCL and aß2GPI assays intended to ameliorate the performance of these solid-phase assays. Despite efforts over the years, standardization has not been reached. This review will focus on methodological issues of the three antiphospholipid antibody (aPL) subtypes that are the subject of debate. The use of an international standard for aPL detection might help solve many of the problems caused by a lack of standardization of these assays.

Evaluation of three commercial ELISA kits for anticardiolipin and anti-beta2-glycoprotein I antibodies in the laboratory diagnosis of the antiphospholipid syndrome.

INTRODUCTION: The laboratory criteria of the antiphospholipid syndrome (APS) include lupus anticoagulant (LAC), anticardiolipin antibodies (aCL) and anti-ß2glycoprotein I antibodies (aß2GPI) IgG or IgM. METHODS: We evaluated three commercial ELISAs for aCL and aß2GPI IgG and IgM: Asserachrom® ('Stago'), Bio-Rad ('BR') and the Bindazyme™ (the Binding Site, 'BS'). RESULTS: Results of all assays and of LAC were correlated with the clinical background (n=228). Sensitivity for Stago/BS/BR aCL IgG was 14%/15%/18%, for aCL IgM 1%/5%/4%, for aß2GPI IgG 9%/10%/17% and for aß2GPI IgM 4%/4%/3%. The specificity for Stago/BS/BR for all assays ranged from 86% to 98%. The positive predictive value (PPV) for Stago/BS/BR aCL IgG was 46%/52%/40%, for aCL IgM 8%/36%/19%, for aß2GPI IgG 70%/67%/45% and for aß2GPI IgM 23%/23%/20%. Combining LAC with aCL and aß2GPI antibodies increased the sensitivity (Stago/BS/BR IgG: 26%/27%/31%, IgM: 22%/21%/26%) and PPV (Stago/BS/BR IgG: 41%/46%/36%, IgM: 34%/40%/36%). Comparing the diagnostic power of the tests, only Stago/BS aß2GPI IgG had a Chi-square P-value lower than 0.05. The combination of LAC and IgG ELISAs of BS resulted in the lowest P-value (0.098) compared to the other combinations. CONCLUSION: All evaluated ELISAs are a practical tool in the laboratory diagnosis of APS. The diagnostic performance shows slight differences between the ELISAs from the different manufacturers.