Measuring Rivaroxaban in a clinical laboratory setting, using common coagulation assays, Xa inhibition and thrombin generation.

BACKGROUND: Rivaroxaban, a direct Xa inhibitor, is one of the new oral antithrombotic agents for which laboratory monitoring is thought to be unnecessary in most cases due to predictable pharmacokinetics. Circumstances are conceivable, however, in which reliable laboratory testing of Rivaroxaban is desirable. The aim of the present in vitro study was to investigate and compare the analytical and practical use of Rivaroxaban monitoring with routine screening assays, thrombin generation and anti-Xa activity, in a clinical laboratory setting. METHODS: Rivaroxaban was added to nine normal donor plasmas and to a normal pooled plasma in concentrations up to 1000 µg/L. Prothrombin time (PT), activated partial thromboplastin time (APTT), endogenous thrombin potential (ETP) and anti-Xa activity were measured in all donor samples. Responsiveness to Rivaroxaban and imprecision of Rivaroxaban recovery were assessed. RESULTS: Low intra-, but high inter-individual imprecision was found for PT displaying a linear dose-response relationship. Imprecision was much lower when directly measuring anti-Xa activity. Responsiveness of ETP lag-time was high, but of total thrombin generation was low, illustrating that the main effect of Rivaroxaban Xa inhibition lies in delaying thrombin formation rather than in preventing it. CONCLUSIONS: Despite a high inter-individual imprecision of the PT, this relatively fast and cost-friendly assay is sensitive to Rivaroxaban and integrates its effects on the global coagulant state of patients. Anti-Xa activity assays can be run to assess the actual Rivaroxaban concentration and in the future ETP could serve as a fine-tuned hemostatic balance indicator for patients using Rivaroxaban.

Pre-acquisition system assessment of the Sysmex(®) Coagulation System CS-2100i and comparison with end-user verification; a model for the regional introduction of new analysers and methods.

BACKGROUND: Pre-acquisition system assessment of clinical laboratory analysers and/or methods are generally repeated independently in each individual organisation planning their introduction. In the course of replacing our 10-year-old Sysmex(®) CA-1500 for Sysmex(®) CS-2100i coagulometers, we designed and tested a model based on CLSI protocols in which one laboratory performs an extensive validation, allowing others to rely on concise verification. METHODS: Validation of the Sysmex(®) CS-2100i was performed largely according to CLSI Guideline H57-A and included EP-5, 7, 9 and 10 in the evaluation of 10 assays encompassing all measurement principles available. EP-15 was used for end-user verification. Practicability and results of validation and verification were compared. RESULTS: Analytical performance of the CS-2100i was as claimed by the manufacturer and complied with our own criteria. System verification results were compatible with those of the validation. Verification was time- and cost-effective. CONCLUSIONS: We have approved the Sysmex(®) CS-2100i analyser for introduction in our laboratory. For colleague laboratories in our region introducing this analyser, a system verification is proposed to be sufficient when referring to our data. It is our intention to use the validation vs. end-user verification model for future method introduction, and when harmonising between our different laboratory locations.

Hemostasis during low molecular weight heparin anticoagulation for continuous venovenous hemofiltration: a randomized cross-over trial comparing two hemofiltration rates.

INTRODUCTION: Renal insufficiency increases the half-life of low molecular weight heparins (LMWHs). Whether continuous venovenous hemofiltration (CVVH) removes LMWHs is unsettled. We studied hemostasis during nadroparin anticoagulation for CVVH, and explored the implication of the endogenous thrombin potential (ETP). METHODS: This cross-over study, performed in a 20-bed teaching hospital ICU, randomized non-surgical patients with acute kidney injury requiring nadroparin for CVVH to compare hemostasis between two doses of CVVH: filtrate flow was initiated at 4 L/h and converted to 2 L/h after 60 min in group 1, and vice versa in group 2. Patients received nadroparin 2850 IU i.v., followed by 380 IU/h continuously in the extracorporeal circuit. After baseline sampling, ultrafiltrate, arterial (art) and postfilter (PF) blood was taken for hemostatic markers after 1 h, and 15 min, 6 h, 12 h and 24 h after converting filtrate flow. We compared randomized groups, and 'early circuit clotting' to 'normal circuit life' groups. RESULTS: Fourteen patients were randomized, seven to each group. Despite randomization, group 1 had higher SOFA scores (median 14 (IQR 11-15) versus 9 (IQR 5-9), p = 0.004). Anti-Xa art activity peaked upon nadroparin bolus and declined thereafter (p = 0.05). Anti-Xa PF did not change in time. Anti-Xa activity was not detected in ultrafiltrate. Medians of all anti-Xa samples were lower in group 1 (anti-Xa art 0.19 (0.12-0.37) vs. 0.31 (0.23-0.52), p = 0.02; anti-Xa PF 0.34 (0.25-0.44) vs. 0.51 (0.41-0.76), p = 0.005). After a steep decline, arterial ETPAUC tended to increase (p = 0.06), opposite to anti-Xa, while postfilter ETPAUC increased (p = 0.001). Median circuit life was 24.5 h (IQR 12-37 h). Patients with 'short circuit life' had longer baseline prothrombin time (PTT), activated thromboplastin time (aPTT), lower ETP, higher thrombin-antithrombin complexes (TAT) and higher SOFA scores; during CVVH, anti-Xa, and platelets were lower; PTT, aPTT, TAT and D-dimers were longer/higher and ETP was slower and depressed. CONCLUSIONS: We found no accumulation and no removal of LMWH activity during CVVH. However, we found that early circuit clotting was associated with more severe organ failure, prior systemic thrombin generation with consumptive coagulopathy, heparin resistance and elevated extracorporeal thrombin generation. ETP integrates these complex effects on the capacity to form thrombin. TRIAL REGISTRATION: Clinicaltrials.gov ID NCT00965328.