Point-of-care testing: state-of-the art and perspectives.

Point-of-care testing (POCT) is becoming an increasingly popular way to perform laboratory tests closer to the patient. This option has several recognized advantages, such as accessibility, portability, speed, convenience, ease of use, ever-growing test panels, lower cumulative healthcare costs when used within appropriate clinical pathways, better patient empowerment and engagement, and reduction of certain pre-analytical errors, especially those related to specimen transportation. On the other hand, POCT also poses some limitations and risks, namely the risk of lower accuracy and reliability compared to traditional laboratory tests, quality control and connectivity issues, high dependence on operators (with varying levels of expertise or training), challenges related to patient data management, higher costs per individual test, regulatory and compliance issues such as the need for appropriate validation prior to clinical use (especially for rapid diagnostic tests; RDTs), as well as additional preanalytical sources of error that may remain undetected in this type of testing, which is usually based on whole blood samples (i.e., presence of interfering substances, clotting, hemolysis, etc.). There is no doubt that POCT is a breakthrough innovation in laboratory medicine, but the discussion on its appropriate use requires further debate and initiatives. This collective opinion paper, composed of abstracts of the lectures presented at the two-day expert meeting "Point-Of-Care-Testing: State of the Art and Perspective" (Venice, April 4-5, 2024), aims to provide a thoughtful overview of the state-of-the-art in POCT, its current applications, advantages and potential limitations, as well as some interesting reflections on the future perspectives of this particular field of laboratory medicine.

Immobility-associated thromboprotection is conserved across mammalian species from bear to human.

Venous thromboembolism (VTE) comprising deep venous thrombosis and pulmonary embolism is a major cause of morbidity and mortality. Short-term immobility-related conditions are a major risk factor for the development of VTE. Paradoxically, long-term immobilized free-ranging hibernating brown bears and paralyzed spinal cord injury (SCI) patients are protected from VTE. We aimed to identify mechanisms of immobility-associated VTE protection in a cross-species approach. Mass spectrometry-based proteomics revealed an antithrombotic signature in platelets of hibernating brown bears with heat shock protein 47 (HSP47) as the most substantially reduced protein. HSP47 down-regulation or ablation attenuated immune cell activation and neutrophil extracellular trap formation, contributing to thromboprotection in bears, SCI patients, and mice. This cross-species conserved platelet signature may give rise to antithrombotic therapeutics and prognostic markers beyond immobility-associated VTE.

Comparison of fecal calprotectin and pancreatic elastase assays based on proficiency testing results.

BACKGROUND: Fecal calprotectin and fecal pancreatic elastase assays are not standardized because of a lack of suitable reference material. Laboratories may have difficulty in switching assays because different manufacturers do not compare well with each other despite having similar reference intervals. Data from proficiency testing performed in Germany (Fecal Diagnostics 01 Survey, INSTAND eV) were investigated to understand how results differed across eight calprotectin and five pancreatic elastase manufacturers. METHODS: Data were collected from participating laboratories in external quality assessment schemes from 2015 to 2020 for calprotectin and 2017 to 2020 for pancreatic elastase. The manufacturer group mean values and standard deviations were calculated. Reference points were created for each external quality assessment scheme by calculating the average of all manufacturer group means. Deming regression analyses were used to observe the differences across manufacturers. RESULTS: The slopes of the Deming regression spanned 0.37-1.91 for calprotectin and 0.84-1.33 for pancreatic elastase. The calprotectin assays had a high degree of variability in quantitative results by manufacturer. However, pancreatic elastase assays appear to be harmonized across the different manufacturer when considering the qualitative interpretation. CONCLUSIONS: Both calprotectin and pancreatic elastase assays could be improved by standardization efforts. Given the clinical utility and our data demonstrating high inter-manufacturer variability, calprotectin should be prioritized over pancreatic elastase in standardization efforts.

Performance testing of four automated coagulation analyzers in a university hospital setting with focus on global coagulation assays.

INTRODUCTION: Several automated coagulation analyzers are available for laboratory use. In a university hospital central laboratory, we compared four different instruments. The results for global coagulation assays are presented here. METHODS: ACL TOP 750 CTS (Instrumentation Laboratory), Atellica COAG 360 (COAG 360), BCS XP (both Siemens Healthineers), and cobas t 711 (Roche Diagnostics) were compared. For inter-instrument comparison, five basic coagulation parameters were analyzed in 476 patient plasma samples. Additional assessments included precision testing using commercial control samples and plasma pools, analysis time for a defined set of samples, sample capacity testing, minimum required sample volumes, and detection quality for hemolytic, icteric, or lipemic (HIL) interferences. RESULTS: Good concordance between different instruments was evident from Bland-Altman plots and comparison of data from each instrument with the overall median (τ≥0.8). Shortest analysis times were found for BCS XP and COAG 360, COAG 360 revealed highest sample capacity. Observed required sample volumes were broadly in line with manufacturer specifications and varied according to instrument configurations. HIL detection differed between instruments and was best with ACL TOP 750 CTS. CONCLUSION: The four analyzers showed similarly high levels of concordance, although some variations were apparent. The most significant differences between the instruments were found in analysis times and sample capacity. Analyzer capabilities must be considered when selecting laboratory equipment and defining algorithms for clinical practice.

A novel approach to laboratory assessment and reporting of platelet von Willebrand factor.

The interaction of platelets with von Willebrand factor is essential for primary hemostasis. Concentration and activity of plasma von Willebrand factor are routine parameters in the assessment of hemostasis disorders. In addition to plasma von Willebrand factor, platelet von Willebrand factor, synthesized in megakaryocytes and stored in α-granules of circulating platelets, is known to contribute to primary hemostasis and the microenvironment of thrombus formation. The laboratory assessment of platelet von Willebrand factor however is cumbersome and not widely established as a routine parameter. We here propose a method for laboratory assessment and reporting of platelet von Willebrand factor potentially useful for laboratory routines in specialized laboratories. Our model allows to describe platelet von Willebrand factor as 1. the concentration of platelet von Willebrand factor in whole blood, 2. the amount of platelet von Willebrand factor in a sample with a defined concentration of 1000 platelets/nl, and 3. the concentration of platelet von Willebrand factor in one platelet. According to our results in healthy individuals, the proportion of platelet von Willebrand factor activity is estimated to be about 10% of total von Willebrand factor in human plasma under physiological circumstances. The concentration of platelet von Willebrand factor is estimated to be 0.4 IU/ml in a sample with a defined concentration of 1000 platelets/nl and to be about 42 IU/ml in one platelet (both expressed as VWF:Ag).

Effects of the Btk-Inhibitors Remibrutinib (LOU064) and Rilzabrutinib (PRN1008) With Varying Btk Selectivity Over Tec on Platelet Aggregation and in vitro Bleeding Time.

Background: Bruton tyrosine kinase inhibitors (BTKi) are used in B-cell malignancies and in development against various autoimmune diseases. Since Btk is also involved in specific pathways of platelet activation, BTKi might be considered to target platelet GPVI/GPIb-mediated atherothrombosis and platelet FcγRIIA-dependent immune disorders. However, BTKi treatment of patients with B-cell malignancies is frequently associated with mild bleeding events caused possibly by off-target inhibition of Tec. Here, we compared the platelet effects of two novel BTKi that exhibit a high (remibrutinib) or low (rilzabrutinib) selectivity for Btk over Tec. Methods and Results: Remibrutinib and rilzabrutinib were pre-incubated with anticoagulated blood. Platelet aggregation and in vitro bleeding time (closure time) were studied by multiple electrode aggregometry (MEA) and platelet-function analyzer-200 (PFA-200), respectively. Both BTKi inhibited atherosclerotic plaque-stimulated GPVI-mediated platelet aggregation, remibrutinib being more potent (IC50 = 0.03 µM) than rilzabrutinib (IC50 = 0.16 µM). Concentrations of remibrutinib (0.1 µM) and rilzabrutinib (0.5 µM), >80% inhibitory for plaque-induced aggregation, also significantly suppressed (>90%) the Btk-dependent pathways of platelet aggregation upon GPVI, von Willebrand factor/GPIb and FcγRIIA activation stimulated by low collagen concentrations, ristocetin and antibody cross-linking, respectively. Both BTKi did not inhibit aggregation stimulated by ADP, TRAP-6 or arachidonic acid. Remibrutinib (0.1 µM) only slightly prolonged closure time and significantly less than rilzabrutinib (0.5 µM). Conclusion: Remibrutinib and rilzabrutinib inhibit Btk-dependent pathways of platelet aggregation upon GPVI, VWF/GPIb, and FcγRIIA activation. Remibrutinib being more potent and showing a better profile of inhibition of Btk-dependent platelet activation vs. hemostatic impairment than rilzabrutinib may be considered for further development as an antiplatelet drug.

[Anticoagulation in intensive care medicine]. / Antikoagulation in der Intensivmedizin.

Critically ill patients are at high risk of hemostasis disorders, which can be associated with both an increased risk of bleeding and an increased risk of thromboembolic events. In the case of acute vascular events, specific therapy with drug anticoagulation or platelet aggregation inhibition is essential. In patients with pre-existing conditions, the appropriate continuation of anticoagulation during intensive care treatment is important. Furthermore, in everyday clinical practice, prophylaxis of thromboembolism as well as the question of potential therapeutic options in the treatment of sepsis and infection-triggered disorders of blood coagulation are important. Specific questions arise with the use of extracorporeal devices such as renal replacement and circulatory assist systems. A number of new anticoagulation and anti-platelet drugs have become available in recent years. Laboratory monitoring of anticoagulation is central. In this overview, current aspects of these topics are presented.

Approximation of emicizumab plasma levels in emergency situations. A practical approach.

INTRODUCTION: A dedicated emicizumab assay based on the modified one-stage factor VIII (FVIII) assay (mOSA) is mainly available in haemophilia treatment centres (HTC). A method to estimate emicizumab plasma levels based on a widely available assay would be desirable, especially for emergency situations. AIM: A method for emicizumab plasma level approximation (ELA) using a routine FVIII activity measurement with standard one-stage assay (sOSA) was developed and evaluated. METHOD: Within this pilot study, 59 samples from patients with severe haemophilia A with (n = 8) and without (n = 8) inhibitors under emicizumab treatment were analysed using sOSA following a manual 1:8 sample pre-test dilution with saline. The sOSA was determined in two different laboratories, using two different analyser platforms each. RESULTS: The results demonstrated an excellent correlation of approximated emicizumab plasma levels (ELA) with the emicizumab plasma concentration determined with mOSA (r > .9; p < .05). The ELA showed a sensitivity of 93.3% and a specificity of 89.6% to predict a pre-defined cut-off-value of ≤30 µg/ml for the discrimination between subtherapeutic and therapeutic emicizumab plasma levels. CONCLUSION: Approximation of emicizumab levels by standard one-stage FVIII assay discriminates between subtherapeutic and therapeutic emicizumab levels and might facilitate clinical decision-making in emergency situations, such as bleeding, trauma or urgent surgery in case that dedicated emicizumab assays are not available.

Laboratory testing in hemophilia: Impact of factor and non-factor replacement therapy on coagulation assays.

The advent of extended half-life (EHL) recombinant clotting factors and innovative non-factor replacement therapeutics, such as emicizumab, offers several advantages over existing products for the prophylactic treatment of people living with hemophilia (PwH). These include low annual bleeding rates with less frequent dosing, higher trough plasma concentrations, and a more convenient route of administration. However, increasing use of these therapies poses challenges to clinicians and coagulation laboratories due to the lack of standardized assays for monitoring of hemostatic parameters, and the potential for misinterpretation of test results, which may jeopardize patient safety. Definitive diagnosis of hemophilia and treatment monitoring is reliant on demonstrating factor VIII (FVIII; hemophilia A) or factor IX (FIX; hemophilia B) deficiency using a functional coagulation assay. The most frequently used assays are based on activated partial thromboplastin time, using a one-stage or two-stage process. While one-stage and chromogenic assays have performed well with human-derived FVIII and FIX and full-length recombinant products, EHL recombinant factors are heterogeneous in structure and mode of action and therefore show wide variation in activity levels between different one-stage assays, and between one-stage and chromogenic assays. In the context of the recommended stepwise approach for laboratory diagnosis of hemophilia, we examine the diagnostic challenges associated with the use of EHL factors and novel non-factor therapeutics and consider the optimal diagnostic approach in PwH who are receiving these treatments. Ultimately, accurate diagnostic solutions are a prerequisite for personalized therapy to minimize treatment burden and improve quality of life in PwH.

Rivaroxaban Reduces Arterial Thrombosis by Inhibition of FXa-Driven Platelet Activation via Protease Activated Receptor-1.

RATIONALE: A reduced rate of myocardial infarction has been reported in patients with atrial fibrillation treated with FXa (factor Xa) inhibitors including rivaroxaban compared with vitamin K antagonists. At the same time, low-dose rivaroxaban has been shown to reduce mortality and atherothrombotic events in patients with coronary artery disease. Yet, the mechanisms underlying this reduction remain unknown. OBJECTIVE: In this study, we hypothesized that rivaroxaban's antithrombotic potential is linked to a hitherto unknown rivaroxaban effect that impacts on platelet reactivity and arterial thrombosis. METHODS AND RESULTS: In this study, we identified FXa as potent, direct agonist of the PAR-1 (protease-activated receptor 1), leading to platelet activation and thrombus formation, which can be inhibited by rivaroxaban. We found that rivaroxaban reduced arterial thrombus stability in a mouse model of arterial thrombosis using intravital microscopy. For in vitro studies, atrial fibrillation patients on permanent rivaroxaban treatment for stroke prevention, respective controls, and patients with new-onset atrial fibrillation before and after first intake of rivaroxaban (time series analysis) were recruited. Platelet aggregation responses, as well as thrombus formation under arterial flow conditions on collagen and atherosclerotic plaque material, were attenuated by rivaroxaban. We show that rivaroxaban's antiplatelet effect is plasma dependent but independent of thrombin and rivaroxaban's anticoagulatory capacity. CONCLUSIONS: Here, we identified FXa as potent platelet agonist that acts through PAR-1. Therefore, rivaroxaban exerts an antiplatelet effect that together with its well-known potent anticoagulatory capacity might lead to reduced frequency of atherothrombotic events and improved outcome in patients.

Oral Bruton tyrosine kinase inhibitors block activation of the platelet Fc receptor CD32a (FcγRIIA): a new option in HIT?

Activation of the platelet Fc-receptor CD32a (FcγRIIA) is an early and crucial step in the pathogenesis of heparin-induced thrombocytopenia type II (HIT) that has not been therapeutically targeted. Downstream FcγRIIA Bruton tyrosine kinase (BTK) is activated; however, its role in Fc receptor-induced platelet activation is unknown. We explored the potential to prevent FcγRIIA-induced platelet activation by BTK inhibitors (BTKi's) approved (ibrutinib, acalabrutinib) or in clinical trials (zanubrutinib [BGB-3111] and tirabrutinib [ONO/GS-4059]) for B-cell malignancies, or in trials for autoimmune diseases (evobrutinib, fenebrutinib [GDC-0853]). We found that all BTKi's blocked platelet activation in blood after FcγRIIA stimulation by antibody-mediated cross-linking (inducing platelet aggregation and secretion) or anti-CD9 antibody (inducing platelet aggregation only). The concentrations that inhibit 50% (IC50) of FcγRIIA cross-linking-induced platelet aggregation were for the irreversible BTKi's ibrutinib 0.08 µM, zanubrutinib 0.11 µM, acalabrutinib 0.38 µM, tirabrutinib 0.42 µM, evobrutinib 1.13 µM, and for the reversible BTKi fenebrutinib 0.011 µM. IC50 values for ibrutinib and acalabrutinib were four- to fivefold lower than the drug plasma concentrations in patients treated for B-cell malignancies. The BTKi's also suppressed adenosine triphosphate secretion, P-selectin expression, and platelet-neutrophil complex formation after FcγRIIA cross-linking. Moreover, platelet aggregation in donor blood stimulated by sera from HIT patients was blocked by BTKi's. A single oral intake of ibrutinib (280 mg) was sufficient for a rapid and sustained suppression of platelet FcγRIIA activation. Platelet aggregation by adenosine 5'-diphosphate, arachidonic acid, or thrombin receptor-activating peptide was not inhibited. Thus, irreversible and reversible BTKi's potently inhibit platelet activation by FcγRIIA in blood. This new rationale deserves testing in patients with HIT.

Replacement Therapy in Patients with Von Willebrand Disease-Indications and Monitoring.

In patients with von Willebrand disease (VWD), replacement therapy may be indicated in the case of spontaneous bleeding, surgical interventions and injuries/trauma or as a prophylaxis of spontaneous bleeding episodes. The deficient von Willebrand factor (VWF) is replaced with or without factor VIII (FVIII). Dual VWF/FVIII concentrates can be beneficial in the case of low FVIII level, while repeated dosing may lead to very high FVIII levels, with a potential thrombogenic effect in individual VWD patients. An excessive FVIII:C increase can be limited by using a VWF product with a low level of FVIII, achieving a haemostatic adequate FVIII:C increase after 6 to 12 hours. Replacement therapy in patients with VWD shall be individualised considering VWD type, history and risk of bleeding and risk of thrombosis, as well as indication and the individually variable VWF and FVIII increase. Deviations from the dosages and minimum trough levels mentioned in guidelines or recommendations can be considered in justified cases. The objective of this review is to provide recommendations for specific constellations of replacement therapy based on the VWD-specific guidelines available in Europe, the available evidence, own experiences and the consensus of the interdisciplinary German author group.

Laboratory Monitoring in Emicizumab-Treated Persons with Hemophilia A.

Hemophilia A (HA) is an X-linked hereditary bleeding disorder caused by deficiency of coagulation factor (F) VIII activity. One of the greatest complications in the treatment of HA is the development of neutralizing alloantibodies, known as FVIII inhibitors. HA patients who develop FVIII inhibitors have limited treatment options available to them and experience greater disease- and treatment-related burdens than HA patients without FVIII inhibitors. Emicizumab, a recently approved bispecific monoclonal antibody, mimics the function of FVIIIa by bridging FIXa and FX to restore effective hemostasis. Although emicizumab and FVIII show some functional similarities, several key differences influence the results of standard laboratory assays when conducted in the presence of emicizumab, and can result in a misleading interpretation of coagulation assays in emicizumab-treated patients. Here, we discuss current laboratory monitoring methods, including activated partial thromboplastin time, FVIII one-stage clotting assays, FVIII chromogenic assays, and global coagulations assays; address why these conventional methods may be inappropriate for monitoring of HA patients receiving emicizumab; and suggest alternative methods applicable to monitoring HA treatment in an evolving treatment landscape.

Emicizumab in the Treatment of Acquired Haemophilia: A Case Report.

The prognosis of acquired haemophilia A (AHA) is severe and treatment options are limited. Emicizumab is a novel bispecific humanized monoclonal antibody in the treatment of inherited AHA with inhibitors. An 83-year-old AHA patient with congestive heart failure and a high risk for thromboembolic and cardiac events who had initially been treated successfully with steroids and substitution of recombinant B-domain-deleted porcine FVIII developed severe bleeding complications and a secondary increase in inhibitor titres after 4 weeks of treatment. Conventional therapeutic strategies failed, and the patient was subsequently treated with emicizumab on off-label and named patient use premises. After the application of emicizumab, the clinical conditions stabilized and no further substitution of coagulation factors was needed. The patient could be discharged and survived 36 days in a cardiac rehabilitation centre without indications for spontaneous bleeding or thromboembolic events. We suggest that the effects of emicizumab in acquired haemophilia should be evaluated in clinical trials.

Optimizing Platelet GPVI Inhibition versus Haemostatic Impairment by the Btk Inhibitors Ibrutinib, Acalabrutinib, ONO/GS-4059, BGB-3111 and Evobrutinib.

Ibrutinib and acalabrutinib are approved for B cell malignancies and novel Bruton's tyrosine kinase (Btk) inhibitors undergo clinical testing also in B cell-driven autoimmune disorders. Btk in platelets mediates platelet activation via glycoprotein (GP) VI, which is crucial for atherosclerotic plaque-induced platelet thrombus formation. This can be selectively inhibited by Btk inhibitors. Since patients on second-generation Btk inhibitors apparently show less bleeding than patients on ibrutinib, we compared the effects of ibrutinib and four novel irreversible Btk inhibitors on GPVI-dependent platelet aggregation in blood and in vitro bleeding time. Low concentrations of collagen which induced the same low degree of GPVI-mediated platelet aggregation as atherosclerotic plaque material were applied. IC50 values for collagen (0.2-0.5 µg/mL)-induced platelet aggregation after 15-minute pre-incubation were: ibrutinib 0.12 µM, BGB-3111 0.51 µM, acalabrutinib 1.21 µM, ONO/GS-4059 1.20 µM and evobrutinib 5.84 µM. Peak venous plasma concentrations of ibrutinib (0.5 µM), acalabrutinib (2 µM) and ONO/GS-4059 (2 µM) measured after anti-proliferative dosage inhibited collagen-induced platelet aggregation, but did not increase PFA-200 closure time on collagen/epinephrine. Closure times were moderately increased by 2- to 2.5-fold higher concentrations of these inhibitors, but not by BGB-3111 (1 µM) and evobrutinib (10 µM). Prolonging platelet drug exposure to 60 minutes lowered IC50 values of any Btk inhibitor for GPVI-mediated aggregation by several fold, and 5- to 10-fold below anti-proliferative therapeutic drug plasma levels. In conclusion, low blood concentrations of ibrutinib and the novel Btk inhibitors suffice for GPVI selective platelet inhibition relevant for atherothrombosis but do not impair primary haemostasis.

Sensitive and specific assessment of recombinant von Willebrand factor in platelet function analyzer.

BACKGROUND: Recombinant von Willebrand factor (rVWF), which was licensed in the United States in 2015, has the multimeric distribution of freshly secreted VWF with ultralarge (UL) and high molecular weight multimers (HMWM) from endothelial cells and megakaryocytes since it has never been exposed to ADAMTS13 or any other proteolytic enzyme. Measurement of closure time (CT) using the platelet function analyzer-200 (PFA-200) is highly sensitive to the presence of UL VWF multimers in added VWF concentrates. The PFA-200 is fully automated and can be used as a reliable point-of-care method to evaluate primary hemostasis. Although it is sensitive to presence of UL VWF multimers, there could be significant clinical utility when used to monitor rVWF replacement therapy. The ability to monitor and optimize the dosing of rVWF contributes to patient safety, especially in situations where the bleeding and thrombotic risk needs to be carefully balanced (e.g., cardiac assist device). OBJECTIVE: The aim of this in-vitro study was to demonstrate the detectability of rVWF spiked in VWF-deficient blood from patients with severe von Willebrand disease (VWD) with quantitative and functional pathologies using a functional testing device. We hypothesized that (1) whole blood samples from VWD patients spiked with rVWF would show a normalization in PFA-CT and (2) that a dose-response relationship could be demonstrated. METHODS AND RESULTS: We selected 12 patients diagnosed with VWD from our database. A therapeutic dose of rVWF product (1 IU/ml) was spiked in VWD patients´ whole blood samples and PFA-CTs were measured. Furthermore, we investigated PFA-CTs under incremental doses of rVWF (0.1, 0.2, and 0.5 IU/ml). The PFA-CTs were normalized in VWD patients´ whole blood samples spiked with rVWF. Additionally, incremental doses of rVWF resulted in a progressive and dose-dependent PFA-CT correction. CONCLUSION: Our in-vitro data indicate that the PFA-200 is a useful tool to detect rVWF. As the PFA-CT correction is dose dependent, the rVWF might be reliably monitored with a point-of-care analytical method during replacement therapy.

Determination of HbA2 by quantitative bottom-up proteomics and isotope dilution mass spectrometry.

BACKGROUND: Poor comparability between laboratories is often observed in the measurement of HbA2. A measurement procedure of higher metrological order is needed for value assignment to a reference material that shall be used as primary calibrator. METHOD: A reference measurement procedure has been developed based on isotope dilution mass spectrometry (IDMS). The α- and δ- subunits are quantified by signature peptides released by tryptic digestion of a 25 µL-blood sample. Full length U-15N-labeled HbA0 and HbA2 are used as internal standards and added to the sample at concentrations closely matching the levels of the natural forms in blood. By this, an improvement in precision could be achieved with respect to previous mass-spectrometry based methods. RESULTS: Recovery of HbA2 added to a blood sample was within 102.6-105.2%. Repeatability and within-laboratory imprecision was <2.0% for two blood samples containing HbA2 at a low and a high fraction. Total combined measurement uncertainty is estimated as 5.5%. Good agreement (r = 0.998) of results was obtained in a comparison of two laboratories using the described IDMS procedure. There is good correlation between commercial analytical systems and IDMS (r = 0.975-0.989). Some of the platforms provide significantly biased results, however, which potentially could be mitigated by reference to IDMS. CONCLUSION: IDMS holds a promise to be suitable as a reference measurement procedure for standardization of HbA2-measurements in laboratory medicine.