Harmonization status of procalcitonin measurements: what do comparison studies and EQA schemes tell us?

Sepsis represents a global health priority because of its high mortality and morbidity. The key to improving prognosis remains an early diagnosis to initiate appropriate antibiotic treatment. Procalcitonin (PCT) is a recognized biomarker for the early indication of bacterial infections and a valuable tool to guide and individualize antibiotic treatment. To meet the increasing demand for PCT testing, numerous PCT immunoassays have been developed and commercialized, but results have been questioned. Many comparison studies have been carried out to evaluate analytical performance and comparability of results provided by the different commercially available immunoassays for PCT, but results are conflicting. External Quality Assessment Schemes (EQAS) for PCT constitute another way to evaluate results comparability. However, when making this comparison, it must be taken into account that the variety of EQA materials consist of different matrices, the commutability of which has not yet been investigated. The present study gathers results from all published comparison studies and results from 137 EQAS surveys to describe the current state-of-the-art harmonization of PCT results. Comparison studies globally highlight a significant variability of measurement results that nonetheless seem to have a moderate impact on medical decision-making. For their part, EQAS for PCT provides highly discrepant estimates of the interlaboratory CV. Due to differences in commutability of the EQA materials, the results from different peer groups could not be compared. To improve the informative value of the EQA data, the existing limitations such as non-harmonized conditions and suboptimal and/or unknown commutability of the EQA materials have to be overcome. The study highlights the need for commutable reference materials that could be used to properly evaluate result comparability and possibly standardize calibration, if necessary. Such an initiative would further improve the safe use of PCT in clinical routine.

Total haemoglobin - a reference measuring system for improvement of standardisation.

Background Total haemoglobin (Hb) concentration in blood belongs to the most requested measurands, and the HiCN method (hemiglobincyanide) is accepted as a reference. Although the reaction principle is clearly characterised, measurement conditions and settings are not consistently defined, some of them influencing the results. An improvement of standardisation is the object. Methods After method optimization, measurement results between different calibration laboratories (CL) were compared with each other and also with results of the National Metrology Institute of Germany (PTB), with target values of certified reference material, within the RELA scheme, and to >1500 results from routine laboratories. Results Overall deviations between three CLs were ≤0.5% (n = 24 samples) in a measurement range of 20 g/L to 300 g/L. A CV of 0.4% was determined in pooled blood (1 year long-term imprecision, 99.0%-101.1% recovery of the mean). For selected measurements (n = 4 samples) the PTB participated without significant differences to three CLs, and no significant differences were observed comparing CLs to certified values of reference materials. The expanded measurement uncertainty (probability 95%) was estimated as 1.1%. Conclusions A reference measuring system, comprising measuring instruments and other devices, including reagents and supply, to generate reference measurement values for total Hb concentration of high accuracy and low measurement uncertainty is presented. Measurement parameters are investigated and defined. The reference measuring system is ready to offer service to EQA providers and to the IVD industry for certifying control materials or calibrators.

Trueness assessment of HbA1c routine assays: are processed EQA materials up to the job?

Background With the worldwide increase of diabetes mellitus prevalence, ensuring that HbA1c assays are accurate is essential. External quality assessment (EQA) programs enable laboratories to verify that analytical methods perform according to the manufacturers' specifications. However, assessing trueness requires commutable materials, a property that is rarely characterized for EQA materials. Methods The difference in bias approach was used to assess commutability of 26 processed quality control materials for 17 of the most frequently used HbA1c assays. Involved assays included immuno-assays, enzymatic assays, affinity, ion-exchange HPLC boronate affinity HPLC and capillary electrophoresis. The measurements were performed at manufacturers or expert laboratories. Assay trueness was additionally assessed against the IFCC reference measurement procedure using fresh clinical specimens that were distributed to 450 medical laboratories. Results Commutability of processed EQA materials was highly heterogeneous and globally insufficient to rigorously assess the trueness of HbA1c assays. Using fresh clinical specimens, mean bias was -0.13 mmol/mol for low HbA1c (34 mmol/mol), between +1.0 and +1.3 mmol/mol for intermediate HbA1c (49 and 58 mmol/mol) and +1.2 mmol/mol for elevated HbA1c (90 mmol/mol). Conclusions This study demonstrates that due to insufficient commutability, most processed EQA materials are unsuitable to assess trueness of HbA1c assays and agreement between the different assays. These materials can only provide information on comparability of individual laboratory results with its peers and on assay precision. Using fresh whole blood samples, this study additionally shows that most HbA1c assays are fairly accurate and meet the total allowable error quality target of 5 mmol/mol.

Higher HbA1c Measurement Quality Standards are Needed for Follow-Up and Diagnosis: Experience and Analyses from Germany.

Measurement of HbA1c is an essential laboratory measure for the follow-up and therapy decision-making in patients with diabetes. HbA1c is one of the measurands in laboratory medicine that have to be successfully checked according to the criteria of the guidelines of the German Medical Association (Rili-BAEK) in external quality assurance using the reference method value concept, when applied in patient care. The allowed deviation of ±18% in external quality assessment (EQA) and ± 10% in internal quality control has been ultimately met by virtually all the different manufacturers and methods. However, such broad limits for permissible deviations are not suitable in view of medical requirements in patient care. The low-level acceptance criteria also depends on the previously used EQA materials used in Germany. In fact, HbA1c measurement results that are imprecisely measured or come from incorrectly calibrated devices are difficult to identify. With implementation of unprocessed fresh EDTA blood, the situation has changed. Until now systems with unit use reagents for point-of-care testing (POCT) of HbA1c are not mandatory to participate in EQA schemes in Germany. This paper outlines why there was a need to narrow the acceptance limits listed within the Rili-BAEK for HbA1c's internal (to ± 3%) and external (to ± 8%) quality controls in EQA schemes for Germany, which will take place after a transition period in the next years. Higher quality in HbA1c measurements will help to avoid misdiagnosis of diabetes as well as potential over- or undertreatment of patients at risk for diabetes.

HbA1c: EQA in Germany, Belgium and the Netherlands using fresh whole blood samples with target values assigned with the IFCC reference system.

BACKGROUND: External quality assessment/proficiency test (EQA/PT) organizers play an important role in monitoring the performance of HbA1c measurements. With increasing quality of the assays, HbA1c is increasingly used for diagnosis of diabetes and the demands on EQA/PT organizers themselves are rising constantly. EQA organizers in Germany (INSTAND), Belgium (WIV/IPV), and the Netherlands (SKML) organized a program with commutable samples and target values assigned with the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference system. The aim of this project was to confirm the logistic feasibility of organizing synchronically in the three countries, an accuracy-based EQA program with fresh whole blood, to investigate the performance of HbA1c assays within and across countries and manufacturers, and to review the EQA acceptance limits. METHODS: Throughout 2015, ten fresh whole blood samples were supplied to the participants. Aggregated results were evaluated according to the IFCC model for quality targets at four levels: overall, per country, per manufacturer, and per country per manufacturer. RESULTS: Robust results in summer and winter demonstrated the feasibility of organizing an EQA with fresh whole blood samples in three countries. The overall performances, as well as the performance for each country were very similar: results fell within the IFCC criteria. Although substantial differences between results from different manufacturers were present, the performances of laboratories using tests of the same manufacturer were strikingly similar in the three countries, suggesting that the quality of HbA1c assays is for the most part manufacturer- related. The improved design of the EQA program also suggested that acceptance limits for performance can be reduced to approximately 8%.

Longitudinal analysis of external quality assessment of immunoassay-based steroid hormone measurement indicates potential for improvement in standardization.

As hormonal disorders are linked to several diseases, the accurate quantitation of steroid hormone levels in serum is crucial in order to provide patients with a reliable diagnosis. Mass spectrometry-based methods are regarded as having the highest level of specificity and sensitivity. However, immunoassays are more commonly used in routine diagnostics to measure steroid levels as they are more cost effective and straightforward to conduct. This study analyzes the external quality assessment results for the measurement of testosterone, progesterone and 17ß-estradiol in serum using immunoassays between early 2020 and May 2022. As reference measurement procedures are available for the three steroid hormones, the manufacturer-specific biases were normalized to the reference measurement values. The manufacturer-specific coefficients of variation were predominantly inconspicuous, below 20% for the three hormones when outliers are disregarded, however there were large differences between the various manufacturer collectives. For some collectives, the median bias to the respective reference measurement value was repeatedly greater than ±35%, which is the acceptance limit defined by the German Medical Association. In the case of testosterone and progesterone determination, some collectives tended to consistently over- or underestimate analyte concentrations compared to the reference measurement value, however, for 17ß-estradiol determination, both positive and negative biases were observed. This insufficient level of accuracy suggests that cross-reactivity continues to be a fundamental challenge when antibody detection is used to quantify steroids with a high structural similarity. Distinct improvements in standardization are required to provide accurate analysis and thus, reliable clinical interpretations. The increased accuracy of the AX immunoassay for testosterone measurement, as observed in the INSTAND EQAs between 2020 and 2022, could be the result of a recalibration of the assay and raises hope for further improvement of standardization of immunoassay-based steroid hormone analyses in the coming years.

Quality assessment of glucose measurement with regard to epidemiology and clinical management of diabetes mellitus in Germany.

Background: During the last decade, Germany has seen an increased prevalence and a redistribution from undetected to diagnosed diabetes mellitus. Due to this substantial epidemiological development, the number of people with documented type 2 diabetes was 8.7 million in 2022. An estimated two million undiagnosed subjects are to be added. Beyond that, the life expectancy of diabetic subjects is increasing due to more responsive health systems in terms of care. Possible reasons include improved screening of at-risk individuals, the introduction of HbA1c for diagnosis in 2010, and the higher use of risk scores. Additionally, quality aspects of the laboratory methodology should be taken into consideration. Methods: Epidemiology and clinical management of diabetes in Germany are presented in the light of publications retrieved by a selective search of the PubMed database. Additionally, the data from German external quality assessment (EQA) surveys for the measurands glucose in plasma and HbA1c in whole blood, reviewed from 2010 until 2022, were evaluated. Above this, data concerning the analytical performance of near-patient glucometer devices, according to the ISO norm 15197:2013, were analyzed. Results: Two laboratory aspects are in good accordance with the observation of an increase in the diabetes mellitus prevalence when retrospectively reviewing the period 2010 to 2022: First, the analytical performance according to the ISO norm 15197:2013 of the glucometer devices widely used by patients with diabetes for the glucose self-testing, has improved during this period. Secondly, concerning the EQA program of INSTAND, the number of participating laboratories raised significantly in Germany. The spreads of variations of the specified results for plasma glucose remained unchanged between 2010 and 2022, whereas for HbA1c a significant decrease of the result scattering could be observed. Conclusion: These retrospectively established findings testify to an excellent analytical quality of laboratory diagnostics for glucose and HbA1c throughout Germany which may be involved in a better diagnosis and therapy of previously undetected diabetes mellitus.

Tolerability of sirolimus: a decade of experience at a single cardiac transplant center.

Sirolimus is used in cardiac transplant recipients to prevent rejection, progression of cardiac allograft vasculopathy, and renal dysfunction. However, sirolimus has many potential side effects and its tolerability when used outside of clinical trials is not well established. We describe a decade of experience with sirolimus in cardiac transplant recipients at our institution. We retrospectively reviewed records of all adult cardiac transplant recipients living between September 1999 and February 2010 (n = 329) and identified 67 patients (20%) who received sirolimus. The indications for sirolimus were cardiac allograft vasculopathy (67%), renal dysfunction (25%), rejection (4%), and intolerability of tacrolimus (3%). One-third of patients discontinued sirolimus at a median (25th, 75th percentiles) of 0.9 (0.2, 1.6) yr of duration. Over 70% of subjects experienced an adverse event attributed to sirolimus. Adverse events were associated with higher average sirolimus levels (9.1 ng/mL vs. 7.1 ng/mL, p = 0.004). We conclude that sirolimus is frequently used in cardiac transplant recipients (20%) and commonly causes side effects, often necessitating discontinuation. Higher average sirolimus levels were associated with adverse events, suggesting that tolerability may improve if levels are maintained within the lower end of the current therapeutic range; however, the improvement in tolerability would need to be balanced with the potential for decreased efficacy.

Proteomic fingerprinting enables quantitative biodiversity assessments of species and ontogenetic stages in Calanus congeners (Copepoda, Crustacea) from the Arctic Ocean.

Species identification is pivotal in biodiversity assessments and proteomic fingerprinting by MALDI-TOF mass spectrometry has already been shown to reliably identify calanoid copepods to species level. However, MALDI-TOF data may contain more information beyond mere species identification. In this study, we investigated different ontogenetic stages (copepodids C1-C6 females) of three co-occurring Calanus species from the Arctic Fram Strait, which cannot be identified to species level based on morphological characters alone. Differentiation of the three species based on mass spectrometry data was without any error. In addition, a clear stage-specific signal was detected in all species, supported by clustering approaches as well as machine learning using Random Forest. More complex mass spectra in later ontogenetic stages as well as relative intensities of certain mass peaks were found as the main drivers of stage distinction in these species. Through a dilution series, we were able to show that this did not result from the higher amount of biomass that was used in tissue processing of the larger stages. Finally, the data were tested in a simulation for application in a real biodiversity assessment by using Random Forest for stage classification of specimens absent from the training data. This resulted in a successful stage-identification rate of almost 90%, making proteomic fingerprinting a promising tool to investigate polewards shifts of Atlantic Calanus species and, in general, to assess stage compositions in biodiversity assessments of Calanoida, which can be notoriously difficult using conventional identification methods.

Results of the first German external quality assessment scheme for the detection of monkeypox virus DNA.

BACKGROUND: In May 2022, the monkeypox virus (MPXV) spread into non-endemic countries and the global community was quick to test the lessons learned from the SARS-CoV-2 pandemic. Due to its symptomatic resemblance to other diseases, like the non-pox virus varicella zoster (chickenpox), polymerase chain reaction methods play an important role in correctly diagnosing the rash-causing pathogen. INSTAND quickly established a new external quality assessment (EQA) scheme for MPXV and orthopoxvirus (OPXV) DNA detection to assess the current performance quality of the laboratory tests. METHODS: We analyzed quantitative and qualitative data of the first German EQA for MPXV and OPXV DNA detection. The survey included one negative and three MPXV-positive samples with different MPX viral loads. The threshold cycle (Ct) or other measures defining the quantification cycle (Cq) were analyzed in an assay-specific manner. A Passing Bablok fit was used to investigate the performance at laboratory level. RESULTS: 141 qualitative datasets were reported by 131 laboratories for MPXV detection and 68 qualitative datasets by 65 laboratories for OPXV detection. More than 96% of the results were correctly identified as negative and more than 97% correctly identified as positive. An analysis of the reported Ct/Cq values showed a large spread of these values of up to 12 Ct/Cq. Nevertheless, there is a good correlation of results for the different MPXV concentrations at laboratory level. Only a few quantitative results in copies/mL were reported (MPXV: N = 5; OPXV: N = 2), but the results correlated well with the concentration differences between the EQA samples, which were to a power of ten each. CONCLUSION: The EQA results show that laboratories performed well in detecting both MPXV and OPXV. However, Ct/Cq values should be interpreted with caution when conclusions are drawn about the viral load as long as metrological traceability is not granted.

Results of German external quality assessment schemes for SARS-CoV-2 antigen detection.

The COVID-19 pandemic illustrated the important role of diagnostic tests, including lateral flow tests (LFTs), in identifying patients and their contacts to slow the spread of infections. INSTAND performed external quality assessments (EQA) for SARS-CoV-2 antigen detection with lyophilized and chemically inactivated cell culture supernatant of SARS-CoV-2 infected Vero cells. A pre-study demonstrated the suitability of the material. Participants reported qualitative and/or quantitative antigen results using either LFTs or automated immunoassays for five EQA samples per survey. 711 data sets were reported for LFT detection in three surveys in 2021. This evaluation focused on the analytical sensitivity of different LFTs and automated immunoassays. The inter-laboratory results showed at least 94% correct results for non-variant of concern (VOC) SARS-CoV-2 antigen detection for viral loads of ≥ 4.75 × 106 copies/mL and SARS-CoV-2 negative samples. Up to 85% had success for a non-VOC viral load of ~ 1.60 × 106 copies/mL. A viral load of ~ 1.42 × 107 copies/mL of the Delta VOC was reported positive in > 96% of results. A high specificity was found with almost 100% negative SARS-CoV-2 antigen results for HCoV 229E and HCoV NL63 positive samples. Quantitative results correlated with increasing SARS-CoV-2 viral load but showed a broad scatter. This study shows promising SARS-CoV-2 antigen test performance of the participating laboratories, but further investigations with the now predominant Omicron VOC are needed.

Sirolimus use and incidence of venous thromboembolism in cardiac transplant recipients.

Sirolimus is an immunosuppressive agent increasingly used in cardiac transplant recipients in the setting of allograft vasculopathy or worsening renal function. Recently, sirolimus has been associated with increased risk of venous thromboembolism (VTE) in lung transplant recipients. To investigate whether this association is also present in cardiac transplant recipients, we retrospectively reviewed the charts of 67 cardiac transplant recipients whose immunosuppressive regimen included sirolimus and 134 matched cardiac transplant recipients whose regimen did not include sirolimus. Rates of VTE were compared. Multivariable Cox proportional hazards models tested the association of sirolimus use with VTE. A higher incidence of VTE was seen in patients treated with vs. without sirolimus (8/67 [12%] vs. 9/134 [7%], log-rank statistic: 4.66, p=0.03). Lower body mass index (BMI) and total cholesterol levels were also associated with VTE (p<0.05). The association of sirolimus with VTE persisted when adjusting for BMI (hazard ratio [95% confidence interval]: 2.96 [1.13, 7.75], p=0.03) but not when adjusting for total cholesterol (p=0.08). These data suggest that sirolimus is associated with an increased risk of VTE in cardiac transplant recipients, a risk possibly mediated through comorbid conditions. Larger, more conclusive studies are needed. Until such studies are completed, a heightened level of awareness for VTE in cardiac transplant recipients treated with sirolimus appears warranted.

[Analytical Quality of Glucose Measurements in Germany]. / Messqualität bei der Glukosemessung im Rahmen der Diabetesdiagnose und -therapie in Deutschland.

The measurement quality of systems used for determination of glucose concentrations has to be sufficiently high to obtain measurement results that are reliable in a clinical context regarding the intended use (e. g., diabetes diagnosis and monitoring). The "Richtlinie der Bundesärztekammer zur Qualitätssicherung laboratoriumsmedizinischer Untersuchungen" (guideline of the German Medical Association on quality assurance in medical laboratory examinations) includes specifications on the internal and external quality assurance that are legally binding for glucose measurements in healthcare. In the opinion of the authors, however, there is room for improvement, and examples are provided. Systems for self-monitoring of blood glucose by patients do not fall under any legally binding requirements for quality assurance. With systems for continuous glucose monitoring, there are currently no technological means to regularly check measurement quality. Additionally, repeated manufacturer-independent evaluations, which could lead to improved measurement quality, are not available.

Procedure for determination of immunosuppressive drugs in whole blood with liquid chromatography-isotope dilution mass spectrometry.

BACKGROUND: Cyclosporin A, sirolimus, tacrolimus, and everolimus are immunosuppressive drugs used for therapy after organ transplantation. There are several analytical procedures for monitoring the drug level in blood, e.g. immunological methods and high-performance liquid chromatography combined with mass spectrometry (MS). From external quality assessment schemes, it became evident that the analytical results show high dispersion and further standardization is required. METHODS: Liquid/liquid extraction of the drugs from whole blood samples was performed using ammonium acetate buffer, pH 9.5, and tert-butylmethyl ether/ethyl acetate (1:1 v/v). Separation of the immunosuppressive drugs was achieved by HPLC using a phenyl-hexyl-RP column with a ternary gradient elution profile, consisting of water, methanol, and acetonitrile containing 0.1% v/v formic acid and 0.1 mmol/L Cs+. Quantification of immunosuppressive drugs was performed by isotope-dilution mass spectrometry using [2H12]-Cyclosporin A [13C, 2H3]-Rapamycin, [13C, 2H2]-Tacrolimus, and [13C2, 2H4]-42-O-(2-Hydroxyethyl)rapamycin as internal standards. RESULTS: The recovery of the new procedure was determined by analysis of spiked blood samples. The recovery in spiked EDTA whole blood samples was 100.8 - 102.5% for cyclosporin A, 101.6 - 103.0% for sirolimus, 100.0 - 101.2% for tacrolimus, and 99.5 - 102.4% for everolimus. The imprecision of the new measurement procedure, expressed as the coefficient of variation (CV), was 1.17 - 2.60% for cyclosporin A in the concentration range between 8.1 and 979 microg/L, 0.92 - 1.72% for sirolimus in the concentration range between 2.1 and 33.2 microg/L, 0.44 - 1.06% for tacrolimus in the concentration range between 2.0 and 30.8 microg/L and 0.82 - 4.34% for everolimus in the concentration range between 2.1 and 31.4 microg/L. CONCLUSIONS: An isotope dilution LC-MS/MS procedure for determination of four immunosuppressive drugs was developed to provide a basis for further development toward a reference measurement procedure.

Liquid chromatography-isotope dilution-mass spectrometry as a new basis for the reference measurement procedure for hemoglobin A1c determination.

BACKGROUND: Standardization of hemoglobin (Hb)A(1c) measurements is a process of considerable interest for quality assurance in diabetes management. To contribute to continuous quality improvement and fulfillment of the requirements for reference measurement procedures according to the standards of the International Organization for Standardization, we developed a calibration system of highest metrological order using isotope dilution-mass spectrometry with a reference material. METHOD: Samples were prepared by enzymatic cleavage based on the IFCC reference measurement procedure for LC-MS analysis. After digestion the samples were spiked with [D7]-labeled glycated and nonglycated hexapeptides as internal standards for quantification. LC-MS analysis was performed by using a C12 reversed-phase column and a gradient of acetonitrile/H(2)O containing 0.1% formic acid. RESULTS: Calibration systems for HbA(1c) determination based on liquid chromatography-isotope dilution-mass spectrometry (LC-ID-MS) and on the IFCC reference measurement procedure were compared. A linear regression analysis demonstrated a correlation of r(2) = 1.00 between the 2 different calibration systems. Mean deviation was 5.5% for the calibration and 3.3% for hemolysate samples, with a mean expanded uncertainty of 4.9%. CONCLUSIONS: This LC-ID-MS procedure allows the current IFCC reference measurement procedure for HbA(1c) to be raised to a higher order of accuracy.

Bridge to heart transplantation with left ventricular assist device versus inotropic agents in status 1 patients.

OBJECTIVE: Left ventricular assist devices (LVADs) are commonly used for critically ill patients awaiting heart transplantation, although their effect on long-term outcomes, relative to inotropic support alone, is still debated. METHOD: Data from Status 1 patients who underwent heart transplantation at our institution between 1990 and 2005 were reviewed (n = 180). They were divided into two groups: those who underwent LVAD implantation as a bridge to transplant (n = 31) and those treated with inotropic agents without the support of LVAD (n = 149). They were compared in terms of demographics and clinical outcome. RESULTS: Both groups were similar in terms of patient and donor demographics. Relative to the inotrope group, the LVAD group did have a longer ischemic time (p = 0.032), a greater incidence of pretransplant transfusion (p < 0.00001), and a greater maximum level of pretransplant panel reactive antibodies (p < 0.001). Creatinine at listing significantly improved in LVAD patients awaiting transplantation (p < 0.0001). Comparisons of 5-year survival in addition to freedom from posttransplant infection, malignancy, revascularization, and acute rejection did not show significant difference between the two groups. The LVAD group did benefit from increased freedom from chronic rejection compared to the inotrope group (p = 0.049). Stepwise Cox Regression did not identify any independent factors affecting patient survival during the first 5 years after transplant. CONCLUSIONS: Status 1 patients successfully bridged to heart transplantation with LVADs had similar long-term clinical outcomes compared to those treated with inotropic agents.

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.