Influence of vitamin K antagonist treatment on activated partial thromboplastin time

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Laboratory Detection of the Antiphospholipid Syndrome via Calibrated Automated Thrombography

Lupus anticoagulants (LAC) consist of anti phospholipid antibodies, detected via their anti coagulant properties in vitro. Strong LAC relate to thromboembolic events, a hallmark of the anti-phospholipid syndrome. We have analyzed whether detection of this syndrome would benefit from thrombin generation measurements. Therefore, calibrated automated thrombography was done in normal plasma (n=30) and LAC patient plasma (n=48 non-anticoagulated, n=12 on oral anti coagulants), diluted 1: 1 with a normal plasma pool. The anti-beta(2)-glycoprotein I monoclonal antibody 23H9, with known LAC properties, delayed the lag time and reduced the peak height during thrombin generation induction in normal plasma dose-dependently (0-150 mu g/ml). At variance, LAC patient 1: 1 plasma mixtures manifested variable lag time prolongations and/or peak height reductions. Coupling these two most informative thrombin generation parameters in a peak height/lag time ratio,and upon normalization versus the normal plasma pool, this ratio distributed normally and was reduced in the plasma mixtures, for 59/60 known LAC plasmas. The normalized peak height/lag time ratio correlated well with the normalized dilute prothrombin time,diluted Russell's viper venom time and silica clotting time, measured in 1: 1 plasma mixtures (correlation coefficients 0.59-0.72). The anticoagulant effects of activated protein C (0-7.5 nM) or 23H9 (0-150 mu g/ml), spiked in the 1: 1 LAC plasma mixtures were reduced for the majority of patients, compatible with functional competition between patient LAC and activated protein C and LAC and 23H9, respectively. Hence,the normalized thrombin gene ration-derived peak height/lag time ratio identifies LAC in plasma with high sensitivity in a single assay, irrespective of the patient's treatment with oral anticoagulants

Evaluation of an automated algorithm for interpretation of lupus anticoagulant testing

Introduction: Lupus anticoagulant (LAC) testing is a multistep procedure including screening, mixing, and confirmation tests. STA Coag Expert is a software module for STA R Max and STA Compact Max analyzers which includes an on-demand LAC algorithm, based on ISTH guidelines, for automatic interpretation, calculation, and launch of assays in LAC interpretation (Stago coag algorithm). Materials and methods: One hundred ninety four patient samples were analyzed in parallel and interpreted manually and automatically by LAC algorithms. LAC algorithms use identical flowcharts and cutoff values as in daily practice. Differently, it only uses index of circulating anticoagulant (ICA), whereas in routine also normalized ratios were assessed for interpretation of mixing tests. Interpretation of dRVVT and aPTT pathways and final conclusions were compared between both approaches. Results: Compared to routine interpretation, LAC algorithm showed a sensitivity of 94% and a specificity of 100% for LAC detection, when discrepancies due to measured clotting times between both analyzers were excluded. Three false negatives were due to different interpretation of dRVVT mixing test. Discrepancies in interpretation of the aPTT mixing test (n=11) did not result in discrepant final LAC result, all having negative confirmation tests. No false positives were observed. With LAC algorithm, hands-on time reduced from 200 to 80minutes. Conclusion: The LAC algorithm of the STA Coag Expert shows good comparability to the manual interpretation of LAC and may be used to assist laboratories in automatic launching of additional tests and in interpretation of LAC according to ISTH guidelines. This way the STA Coag Expert LAC algorithm may improve interlaboratory and STA comparability of LAC results

Influence of anticardiolipin and anti-β2 glycoprotein I antibody cutoff values on antiphospholipid syndrome classification

Background: Anticardiolipin (aCL) and anti-beta 2 glycoprotein I (a beta 2GPI) immunoglobulin (Ig) G/IgM antibodies are 2 of the 3 laboratory criteria for classification of antiphospholipid syndrome (APS). The threshold for clinically relevant levels of antiphospholipid antibodies (aPL) for the diagnosis of APS remains a matter of debate. The aim of this study was to evaluate the variation in cutoffs as determined in different clinical laboratories based on the results of a questionnaire as well as to determine the optimal method for cutoff establishment based on a clinical approach.Methods: The study included samples from 114 patients with thrombotic APS, 138 patients with non-APS thrombosis, 138 patients with autoimmune disease, and 183 healthy controls. aCL and a beta 2GPI IgG/IgM antibodies were measured at 1 laboratory using 4 commercial assays. Assay-specific cutoff values for aPL were obtained by determining 95th and 99th percentiles of 120 compared to 200 normal controls by different statistical methods.Results: Normal reference value data showed a nonparametric distribution. Higher cutoff values were found when calculated as 99th rather than 95th percentiles. These values also showed a stronger association with thrombosis. The use of 99th percentile cutoffs reduced the chance of false positivity but at the same time reduced sensitivity. The decrease in sensitivity was higher than the gain in specificity when 99th percentiles were calculated by methods wherein no outliers were eliminated.Conclusions: We present cutoff values for aPL determined by different statistical methods. The 99th percentile cutoff value seemed more specific. However, our findings indicate the need for standardized statistical criteria to calculate 99th percentile cutoff reference values.Background: Anticardiolipin (aCL) and anti-beta 2 glycoprotein I (a beta 2GPI) immunoglobulin (Ig) G/IgM antibodies are 2 of the 3 laboratory criteria for classification of antiphospholipid syndrome (APS). The threshold for clinically relevant levels of antiphospholipid antibodies (aPL) for the diagnosis of APS remains a matter of debate. The aim of this study was to evaluate the variation in cutoffs as determined in different clinical laboratories based on the results of a questionnaire as well as to determine the optimal method for cutoff establishment based on a clinical approach.Methods: The study included samples from 114 patients with thrombotic APS, 138 patients with non-APS thrombosis, 138 patients with autoimmune disease, and 183 healthy controls. aCL and a beta 2GPI IgG/IgM antibodies were measured at 1 laboratory using 4 commercial assays. Assay-specific cutoff values for aPL were obtained by determining 95th and 99th percentiles of 120 compared to 200 normal controls by different statistical methods.Results: Normal reference value data showed a nonparametric distribution. Higher cutoff values were found when calculated as 99th rather than 95th percentiles. These values also showed a stronger association with thrombosis. The use of 99th percentile cutoffs reduced the chance of false positivity but at the same time reduced sensitivity. The decrease in sensitivity was higher than the gain in specificity when 99th percentiles were calculated by methods wherein no outliers were eliminated.Conclusions: We present cutoff values for aPL determined by different statistical methods. The 99th percentile cutoff value seemed more specific. However, our findings indicate the need for standardized statistical criteria to calculate 99th percentile cutoff reference values.A

Monitoring of anticoagulation in thrombotic antiphospholipid syndrome

Anticoagulation is central to the management of thrombotic antiphospholipid syndrome (APS). The standard anticoagulant treatment for thrombotic APS is life-long warfarin or an alternative vitamin K antagonist. The role of direct oral anticoagulants for thrombotic APS is not established due to the lack of definitive evidence and has recently been addressed in international guidance. Other anticoagulant options include low molecular weight heparin, unfractionated heparin, and fondaparinux. In APS patients, lupus anticoagulant can affect phospholipid-dependent coagulation monitoring tests, so that they may not reflect true anticoagulation intensity. Accurate assessment of anticoagulation intensity is essential, to optimize anticoagulant dosing and facilitate thrombus resolution; minimize the risk of recurrent thrombosis or bleeding; inform assessment of whether recurrent thrombosis is related to breakthrough thrombosis while on therapeutic anticoagulation, subtherapeutic anticoagulation, non-adherence, or spurious results; and guide the management of bleeding. Knowledge of anticoagulant intensity also informs assessment and comparison of anticoagulation regimens in clinical studies. Considerations regarding anticoagulation dosing and/or monitoring of thrombotic APS patients underpin appropriate management in special situations, notably APS-related severe renal impairment, which can occur in APS or APS/systemic lupus erythematosus-related nephropathy or catastrophic APS; and APS-related thrombocytopenia. Anticoagulant dosing and monitoring in thrombotic APS patients also require consideration in anticoagulant-refractory APS and during pregnancy. In this review, we summarize the tests generally used in monitoring anticoagulant therapy, use of the main anticoagulants considered for thrombotic APS, lupus anticoagulant effects on anticoagulation monitoring tests, and strategies for appropriate anticoagulant monitoring in thrombotic APS

Where and when to inject low molecular weight heparin in hemodiafiltration? : a cross over randomised trial

Background and Objective : Low molecular weight heparins (LMWHs) are small enough to pass large pore dialysis membranes. Removal of LMWH if injected before the start of the session is possible during high-flux dialysis and hemodiafiltration. The aim of this study was to determine the optimal mode (place and time) of tinzaparin administration during postdilution hemodiafiltration. Study Design, Setting, Patients : In 13 chronic hemodiafiltration patients, 3 approaches of injection were compared in a randomised cross over trial: i) before the start of the session at the inlet blood line filled with rinsing solution (IN0), ii) 5 min after the start at the inlet line filled with blood (IN5) and iii) before the start of the session at the outlet blood line (OUT0). Anti-Xa activity, thrombin generation, visual clotting score and reduction ratios of urea and beta2microglobulin were measured. Results : Anti-Xa activity was lower with IN0 compared with IN5 and OUT0, and also more thrombin generation was observed with IN0. No differences were observed in visual clotting scores and no clinically relevant differences were observed in solute reduction ratio. An anti-Xa of 0.3 IU/mL was discriminative for thrombin generation. Anti-Xa levels below 0.3 IU/mL at the end of the session were associated with worse clotting scores and lower reduction ratio of urea and beta2microglobulin. Conclusions : Injection of tinzaparin at the inlet line before the start of postdilution hemodiafiltration is associated with loss of anticoagulant activity and can therefore not be recommended. Additionally, we found that an anti-Xa above 0.3 IU/mL at the end of the session is associated with less clotting and higher dialysis adequacy