Meijer, Piet

AbstractThis guidance document has been prepared on behalf of the International Council for Standardisation in Hematology. The aim of the document is to provide guidance and recommendations on the measurement of factor VIII (FVIII) and factor IX (FIX) inhibitors. After an introduction on the clinical background and relevance of factor VIII and factor IX inhibitor testing, the following aspects of laboratory testing are included: screening for inhibitors, assay principle, sample requirements, testing requirements and interpretation, quality assurance, interferences and recent developments. This guidance document focusses on recommendations for a standardised procedure for the laboratory measurement of FVIII and FIX type I inhibitors. The recommendations are based on published data in peer‐reviewed literature and expert opinion.

AbstractBackgroundLaboratory diagnosis of von Willebrand Disease (VWD) is complex. Reliance on laboratory testing can be problematic as different VWD screening panels, assays and methodologies can produce analytic variability in test results.ObjectivesTo compare the degree of imprecision among the VWD assays and within the platelet binding activity (PBA) assays, to determine the consensus among the VWD assays for correct classification of sample results, and to determine consensus among laboratories’ von Willebrand factor (VWF) multimer interpretations and final interpretations of the VWD panels.Patients/MethodsProficiency testing results from the North American Specialized Coagulation Laboratory Association (NASCOLA) submitted by laboratories from 2010 to 2019 for all normal, type (T) 1 VWD and T2 VWD samples were analysed.Results and ConclusionsImprecision was lowest for VWF antigen and highest for collagen binding activity (CBA) with median coefficient of variation (CV) of 12% (interquartile range (IQR) 7%) and 23% (IQR 21%) respectively. Within the VWF PBA assays, the gain‐of‐function mutant GP1b binding (VWF: GP1bM) methods had the least imprecision (CV 9%, IQR 10%). All assays, including the various PBA methods had excellent consensus. The majority of laboratories agreed that normal (median consensus‐82%, IQR 16%) and T1 VWD (median consensus‐100%, IQR 9%) samples had normal multimer distribution. Consensus among laboratories for final interpretations was excellent for normal samples (median 81%, IQR 8%), good for T1 VWD samples (median 59%, IQR 9%), and fair for T2 VWD samples (median 44%, IQR 21%). Consensus on final interpretation decreased as sample complexity increased.

AbstractIntroductionPlatelet function disorders (PFD) are an important group of bleeding disorders that require validated and practical laboratory strategies for diagnosis.MethodsThis review summarizes the authors’ experiences, current literature, and an international survey to evaluate the practices of diagnostic laboratories that offer tests for PFD.ResultsBlood counts, blood film review, and aggregation tests are the most commonly performed investigations for PFD and help determine whether there is thrombocytopenia and/or defective platelet function due to a variety of causes. The performance characteristics of tests for PFD, and the level of evidence that these tests detect bleeding problems, are important issues to determine where tests are useful for diagnostic or correlative purposes, or research only uses. Platelet aggregation assays, and quantitative analysis of platelet dense granule numbers, are tests with good performance characteristics that detect abnormalities associated with increased bleeding in a significant proportion of individuals referred for PFD investigations. Lumiaggregometry estimates of platelet adenosine triphosphate release show greater variability which limits the diagnostic usefulness. Diagnostic laboratories report that fiscal and other constraints, including a lack of high‐quality evidence, limit their ability to offer an expanded test menu for PFD.ConclusionPFD are clinically important bleeding disorders that remain challenging for diagnostic laboratories to investigate. While some PFD tests are well validated for diagnostic purposes, gaps in scientific evidence and resource limitations influence diagnostic laboratory decisions on which PFD tests to offer.

Rivaroxaban and dabigatran are among the newest anticoagulants, and measuring their concentration in patients is a new challenge for clinical laboratories. We analyzed data from the ECAT proficiency program to determine how well the assays are performing in clinical laboratories internationally. Most laboratories received a passing grade (Z score <3) for the results of their dabigatran and rivaroxaban testing. Failing Z scores were not associated with any particular method. With dabigatran, some homemade calibrators gave higher results than the commercially available calibrators. There were no significant differences among the instruments or the 5 reagents in use, but results showed inter‐laboratory variability that could have clinical significance. The 3 reagents with the lowest number of users had poor inter‐laboratory precision. Ten different anti‐Xa reagents were in use for rivaroxaban testing. One reagent gave lower results than other reagents at 100 ng/mL but not at 300 ng/mL. There were no significant differences among the different rivaroxaban calibrators or instruments. In conclusion, inter‐laboratory precision could be improved for both dabigatran and rivaroxaban assays. Homemade dabigatran calibrators differed from commercially available calibrators, and there was a statistically significant difference between some of the rivaroxaban reagents. About 10% of results received failing Z scores or passed but fell in a range that require the laboratory to investigate for bias or other inaccuracy in their method. Am. J. Hematol. 91:E464–E467, 2016. © 2016 Wiley Periodicals, Inc.

SummaryIntroductionThe performance of factor XI activity (FXI) by laboratories in the North American Specialized Coagulation Laboratory Association proficiency testing program was analyzed.MethodsOver 10 years (2003–2013), 80 samples were distributed; 33–55 laboratories participated per exercise providing 3833 total responses. Analysis was performed on numeric results and qualitative classification of results.ResultsThe sample FXI levels ranged from 3.8 to 154.0 IU/dL. The overall interlaboratory average coefficient of variation (CV%) was 17.5%; the CV was higher for a sample with low (3.8 IU/dL) FXI. Results were correctly classified as abnormal (100%) for a sample with 3.8 IU/dL FXI and normal/borderline normal (97.7%) for 45 samples with 80 to < 140 IU/dL FXI. The classification was heterogeneous for samples with FXI of 50 to < 80 IU/dL. Six specimens were repeat‐tested from 2007 to 2013. The mean FXI was not significantly different in laboratories using the same method on both exercises, suggesting good intralaboratory precision over time. Univariate analysis of data from 2011 to 2012 did not find a consistent significant difference among the activators, analyzers, calibrators, and FXI‐deficient plasmas.ConclusionLaboratories generally performed well in assessment of FXI based on interlaboratory precision when FXI >30 IU/dL and on classification of samples with very low or normal FXI.