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%.

A new statistical method for evaluating long-term analytical performance of laboratories applied to an external quality assessment scheme for flow cytometry.

BACKGROUND: The Belgian External Quality Assessment Scheme for Flow Cytometry evaluates the long-term analytical performance of participating laboratories by calculating a regression line between the target and reported values of each parameter for each laboratory during the past 3 years. This study aims to develop a method to find laboratories with aberrant variability or bias using robust techniques and to obtain robust estimates of the variability. METHODS: A method is proposed to find outliers with respect to the individual regression line, followed by a step to find regression lines with excessive variability and finally a step to find regression lines with high bias. RESULTS: The model was applied to the results obtained by 52 laboratories for CD4%. From the 1340 data points, 35 were determined to be regression outliers. The second step revealed one regression line with excessive variability; the third step detected three regression lines with exceeding bias. CONCLUSIONS: The methodology allows assessment of the long-term performance of laboratories, taking into account samples with different target values. Outliers in the first step indicate accidental mistakes, outliers in the second and third step point to high analytical variability or bias.

Iron-binding antioxidant capacity is impaired in diabetes mellitus.

Increased lipid peroxidation contributes to diabetic complications and redox-active iron is known to play an important role in catalyzing peroxidation reactions. We aimed to investigate if diabetes affects the capacity of plasma to protect against iron-driven lipid peroxidation and to identify underlying factors. Glycemic control, serum iron, proteins involved in iron homeostasis, plasma iron-binding antioxidant capacity in a liposomal model, and non-transferrin-bound iron were measured in 40 type 1 and 67 type 2 diabetic patients compared to 100 nondiabetic healthy control subjects. Iron-binding antioxidant capacity was significantly lower in the plasma of diabetic subjects (83 +/- 6 and 84 +/- 5% in type 1 and type 2 diabetes versus 88 +/- 6% in control subjects, p < 0.0005). The contribution of transferrin, ceruloplasmin, and albumin concentrations to the iron-binding antioxidant capacity was lost in diabetes (explaining only 4.2 and 6.3% of the variance in type 1 and type 2 diabetes versus 13.9% in control subjects). This observation could not be explained by differences in Tf glycation, lipid, or inflammatory status and was not associated with higher non-transferrin-bound iron levels. Iron-binding antioxidant capacity is decreased in diabetes mellitus.

A novel method to quantify in vivo transferrin glycation: applications in diabetes mellitus.

BACKGROUND: In vitro glycation of transferrin leads to increased oxidative stress by impairing iron-binding antioxidant capacity. The aim of this study is to develop a method to evaluate in vivo transferrin glycation in diabetes. METHODS: We adapted the nitroblue tetrazolium assay to measure in micro-well plates the fructosamine content of transferrin isolated from serum by immunocomplexation. RESULTS: Introduction of the immunocomplexation step did not affect the analytical performance of the fructosamine measurement and analytical variability was lower than 7%. The diabetic group (n=107) had significantly higher transferrin glycation (1.39+/-1.12 versus 0.79+/-1.09 micromol fructosamine/g transferrin in the non-diabetic group, n=91, p<0.0005) and this was most pronounced in type 1 diabetes (1.95+/-1.02 versus 1.06+/-1.04 micromol fructosamine/g transferrin in type 2, p<0.0005). Transferrin glycation was associated with parameters of glycaemic control but did not correlate with serum iron or total iron-binding capacity. Total iron-binding capacity was lower in type 1 diabetes (63+/-9 versus 69+/-12 micromol/l in type 2, p<0.05) and was mainly determined by transferrin concentration. CONCLUSIONS: These results indicate that the adapted nitroblue tetrazolium assay combined with immunocomplexation of serum transferrin is suitable to detect differences in in vivo transferrin glycation between non-diabetic, type 1 and type 2 diabetic subjects.

Verification of chemistry reference ranges using a simple method in sub-Saharan Africa.

BACKGROUND: Chemistry safety assessments are interpreted by using chemistry reference ranges (CRRs). Verification of CRRs is time consuming and often requires a statistical background. OBJECTIVES: We report on an easy and cost-saving method to verify CRRs. METHODS: Using a former method introduced by Sigma Diagnostics, three study sites in sub-Saharan Africa, Bondo, Kenya, and Pretoria and Bloemfontein, South Africa, verified the CRRs for hepatic and renal biochemistry assays performed during a clinical trial of HIV antiretroviral pre-exposure prophylaxis. The aspartate aminotransferase/alanine aminotransferase, creatinine and phosphorus results from 10 clinically-healthy participants at the screening visit were used. In the event the CRRs did not pass the verification, new CRRs had to be calculated based on 40 clinically-healthy participants. RESULTS: Within a few weeks, the study sites accomplished verification of the CRRs without additional costs. The aspartate aminotransferase reference ranges for the Bondo, Kenya site and the alanine aminotransferase reference ranges for the Pretoria, South Africa site required adjustment. The phosphorus CRR passed verification and the creatinine CRR required adjustment at every site. The newly-established CRR intervals were narrower than the CRRs used previously at these study sites due to decreases in the upper limits of the reference ranges. As a result, more toxicities were detected. CONCLUSION: To ensure the safety of clinical trial participants, verification of CRRs should be standard practice in clinical trials conducted in settings where the CRR has not been validated for the local population. This verification method is simple, inexpensive, and can be performed by any medical laboratory.

Transferrin modifications and lipid peroxidation: implications in diabetes mellitus.

Free iron is capable of stimulating the production of free radicals which cause oxidative damage such as lipid peroxidation. One of the most important mechanisms of antioxidant defense is thus the sequestration of iron in a redox-inactive form by transferrin. In diabetes mellitus, increased oxidative stress and lipid peroxidation contribute to chronic complications but it is not known if this is related to abnormalities in transferrin function. In this study we investigated the role of transferrin concentration and glycation. The antioxidant capacity of apotransferrin to inhibit lipid peroxidation by iron-binding decreased in a concentration-dependent manner from 89% at > or = 2 mg/ml to 42% at 0.5 mg/ml. Pre-incubation of apotransferrin with glucose for 14 days resulted in a concentration-dependent increase of glycation: 1, 5 and 13 micromol fructosamine/g transferrin at 0, 5.6 and 33.3 mmol/l glucose respectively, p < 0.001. This was accompanied by a decrease in the iron-binding antioxidant capacity of apotransferrin. In contrast, transferrin glycation by up to 33.3 mmol/l glucose did not affect chemiluminescence-quenching antioxidant capacity, which is iron-independent. Colorimetric evaluation of total iron binding capacity in the presence of an excess of iron (iron/transferrin molar ratio = 2.4) also decreased from 0.726 to 0.696 and 0.585mg/g transferrin after 0, 5.6 and 33.3 mmol/l glucose, respectively, p < 0.01. In conclusion, these results suggest that lower transferrin concentration and its glycation can, by enhancing the pro-oxidant effects of iron, contribute to the increased lipid peroxidation observed in diabetes.

Comparison of different approaches to evaluate External Quality Assessment Data.

In EQA programs, Z-scores are used to evaluate laboratory performance. They should indicate poorly performing laboratories, regardless of the presence of outliers. For this, two different types of approaches exist. The first type are "outlier-based" approaches, which first exclude outlying values, calculate the average and standard deviation on the remaining data and obtain Z-scores for all values (e.g., Grubbs and Dixon). The second type includes the "robust" approaches (e.g., Tukey and Qn or the algorithm recommended by ISO). The different approaches were assessed by randomly generated samples from the Normal and Student t distributions. Part of the sample data were contaminated with outliers. The number of false and true outliers was recorded and subsequently, Positive and Negative Predictive Values were derived. Also, the sampling mean and variability were calculated for location and scale estimators. The various approaches performed similarly for sample sizes above 10 and when outliers were at good distance from the centre. For smaller sample sizes and closer outliers, however, the approaches performed quite differently. Tukey's method was characterised by a high true and a high false outlier rate, while the ISO and Qn approaches demonstrated weak performance. Grubbs test yielded overall the best results.

Current practices in antinuclear antibody testing: results from the Belgian External Quality Assessment Scheme.

BACKGROUND: This study aimed to assess the state-of-the-art of antinuclear antibody (ANA) testing as practiced in the Belgian and Luxembourg laboratories, using the results obtained in the Belgian National External Quality Assessment Scheme from 2000 to 2005. METHODS: During this period, nine samples with different specificities were sent for analysis. Participants were surveyed for methodology used and were asked to report staining pattern and titer of ANAs. In 2002, an attempt was made to improve the comparability of quantitative ANA results by the provision of a commercial reference material and to relate observed differences to methodology. RESULTS: With one exception, all participants employed a microscope-based indirect immunofluorescence assay with human epithelial cell line 2 cells. Most laboratories were accurate in describing the pattern. The percentage of unacceptable answers was greater for samples with borderline levels of antibody and for samples showing a cytoplasmic pattern. An improvement in the detection of anticentromere antibodies was observed. For all samples, a wide range of titers was reported. The provision of the secondary reference preparation led to improved inter-laboratory concordance. Comparison of methodology variables revealed a correlation between unstandardized titers and the power of the lamp of the microscope and the use of a dark room. CONCLUSIONS: The EQAS results presented in this work provide valuable insights into the state of the art of ANA testing as practiced in the Belgian and Luxembourg Laboratories and illustrate the important value of a national EQAS for ANA testing as a tool to improve performance and interlaboratory comparability of laboratory results.

Iron-induced oxidative stress in haemodialysis patients: a pilot study on the impact of diabetes.

BACKGROUND: Administration of intravenous iron preparations in haemodialysis patients may lead to the appearance of non-transferrin bound iron which can catalyse oxidative damage. We investigated this hypothesis by monitoring the oxidative stress of haemodialysis patients and the impact of iron and diabetes mellitus herein. MATERIALS AND METHODS: Baseline values of serum iron and related proteins, transferrin glycation, non-transferrin bound iron, antioxidant capacity and lipid peroxidation (malondialdehyde) of 11 haemodialysis patients (six non-diabetic and five type 2 diabetes) were compared to those of non-haemodialysis control subjects (non-diabetic and type 2 diabetes). Changes in these parameters were monitored during haemodialysis before and after iron administration. RESULTS: Baseline values of malondialdehyde correlated with ferritin concentration (r = 0.664, P = 0.036) and were elevated to the same extent in non-diabetic and diabetic haemodialysis patients (median of 1.09 compared to 0.60 mumol/l in control persons, P < 0.02). After iron infusion, transferrin saturation increased more markedly in non-diabetic subjects from 28% to 185% vs. from 33% to 101% in diabetic patients (P = 0.008). This increase was accompanied by the appearance of non-transferrin bound iron (5.91 +/- 1.33 micromol/l), a loss in plasma iron-binding antioxidant capacity and a further increase in malondialdehyde which was more pronounced in diabetic patients (from 0.93 +/- 0.30 micromol/l to 2.21 +/- 0.69 micromol/l vs. from 1.21 +/- 0.42 micromol/l to 1.86 +/- 0.56 micromol/l in the non-diabetic subjects, P = 0.046). CONCLUSIONS: In haemodialysis patients, higher lipid peroxidation is determined by higher body iron stores. The increase induced by iron infusion is accompanied by a loss in iron-binding antioxidant capacity and is more pronounced in diabetes mellitus.

Impact of diabetes mellitus on the relationships between iron-, inflammatory- and oxidative stress status.

BACKGROUND: Diabetes is an inflammatory condition associated with iron abnormalities and increased oxidative damage. We aimed to investigate how diabetes affects the interrelationships between these pathogenic mechanisms. METHODS: Glycaemic control, serum iron, proteins involved in iron homeostasis, global antioxidant capacity and levels of antioxidants and peroxidation products were measured in 39 type 1 and 67 type 2 diabetic patients and 100 control subjects. RESULTS: Although serum iron was lower in diabetes, serum ferritin was elevated in type 2 diabetes (p = 0.02). This increase was not related to inflammation (C-reactive protein) but inversely correlated with soluble transferrin receptors (r = - 0.38, p = 0.002). Haptoglobin was higher in both type 1 and type 2 diabetes (p < 0.001) and haemopexin was higher in type 2 diabetes (p < 0.001). The relation between C-reactive protein and haemopexin was lost in type 2 diabetes (r = 0.15, p = 0.27 vs r = 0.63, p < 0.001 in type 1 diabetes and r = 0.36, p = 0.001 in controls). Haemopexin levels were independently determined by triacylglycerol (R(2) = 0.43) and the diabetic state (R(2) = 0.13). Regarding oxidative stress status, lower antioxidant concentrations were found for retinol and uric acid in type 1 diabetes, alpha-tocopherol and ascorbate in type 2 diabetes and protein thiols in both types. These decreases were partially explained by metabolic-, inflammatory- and iron alterations. An additional independent effect of the diabetic state on the oxidative stress status could be identified (R(2) = 0.5-0.14). CONCLUSIONS: Circulating proteins, body iron stores, inflammation, oxidative stress and their interrelationships are abnormal in patients with diabetes and differ between type 1 and type 2 diabetes.

Cell-mediated LDL oxidation: the impact of transition metals and transferrin.

Activated monocytes release oxygen radicals by respiratory burst and oxidative damage can be accelerated by transition metals. We investigated the cell-mediated and metal-catalysed in vitro oxidation of low-density lipoproteins (LDL), as well as the impact of the metal-binding protein transferrin (Tf). LDL oxidation was measured by monitoring the increase in fluorescence (350/440 nm excitation/emission). Maximal respiratory burst by U937 cells was achieved after 96 h differentiation with retinoic acid and dihydroxyvitamin D3 followed by stimulation with opsonised zymosan. Addition of activated cells resulted in the LDL oxidation, even in the absence of transition metals. Moreover, activated cells greatly enhanced metal-catalysed oxidative modifications, especially in the presence of copper. By binding metals, Tf was able to strongly impair this process. In conclusion, by generating oxygen radicals, activated U937 cells were able to oxidise LDL. The oxidising process was most pronounced in the presence of copper and could be blocked by Tf.

Effects of Atorvastatin on LDL sub-fractions and peroxidation in type 1 diabetic patients: a randomised double-blind placebo-controlled study.

BACKGROUND: Patients with diabetes have an increased risk of both developing and dying from cardiovascular disease, and, currently, more aggressive lipid-lowering targets are being recommended for these patients. Statins are widely and successfully used to correct dyslipidemia and prevent acute coronary episodes, but their effects on lipoprotein composition and peroxidation have not been fully investigated. We aimed to address this issue in type 1 diabetes mellitus. METHODS: T1DM patients with atherogenic index (total/HDL-cholesterol > 4) were randomised double-blindly to group A (n = 12) that received Atorvastatin 40 mg/day and group P (n = 12) that received placebo. They were monitored for blood biochemistry, LDL sub-fractions and lipid peroxidation at inclusion, after 6 and after 12 weeks. RESULTS: In group A, the 40% decrease in serum total and LDL cholesterol and 20% decrease in triglycerides was accompanied by a decrease in serum alpha-tocopherol from 46.4 +/- 16.3 (mean +/- SD) at inclusion to 32.2 +/- 11.8 and 32.6 +/- 14.0 micromol/L after 6 and 12 weeks respectively (p < 0.001 compared to group P by repeated-measures ANOVA). Relative to LDL + VLDL cholesterol, alpha-tocopherol increased by 40% (p < 0.001). Copper-induced LDL + VLDL peroxidation increased from 4891 +/- 1325 at inclusion to 6821 +/- 2291 and 7040 +/- 1712 nmol TBARS/mg LDL + VLDL cholesterol produced in 3 h (p = 0.004). LDL sub-fractions shifted towards the less dense regions (p = 0.03). CONCLUSIONS: These results suggest that Atorvastatin lowers the antioxidant capacity of LDL and VLDL in T1DM. The mechanisms underlying these changes merit further investigation and should be taken into account when planning long-term primary prevention of CHD in diabetes.

Effects of in vitro glycation on Fe3+ binding and Fe3+ isoforms of transferrin.

BACKGROUND: In diabetes, protein function is altered by glycation, but the impact on the Fe3+ binding and antioxidant functions of transferrin (Tf) is largely unknown. The aim of the present study was to investigate the effects of glycation on the distribution of Fe3+ on the two Fe3+ -binding sites of Tf. METHODS: In vitro glycation of Tf was accomplished by preincubation with glucose for 14 days. Tf was loaded with Fe3+ compounds to achieve theoretical Tf Fe3+ saturations of 32%, 64%, and 96% (monitored by spectrophotometry). Fe3+ -Tf isoforms were separated by isoelectric focusing. RESULTS: Fe3+ binding was highest when Tf was incubated with Fe:nitrilotriacetic acid and reached a steady state overnight. Increasing the Fe3+ load led to a shift of isoform profile toward the diferric form (Fe2-Tf): in freshly prepared Tf, Fe2-Tf represented 6%, 30%, and 66% of all isoforms at 32%, 64%, and 96% theoretical Fe3+ saturation, respectively. Fe3+ was equally distributed to the monoferric Tf forms with Fe3+ bound to the amino (Fe1N-Tf) and carboxy termini (Fe1C-Tf). Glycation decreased binding of Fe3+ to Tf (monitored at 450 nm). At low theoretical Fe3+ saturation (32%), glycation increased the mean (SD) proportion of Fe2-Tf: 18 (3)% in the presence of 33.3 mmol/L glucose vs 12 (4)% with 0 mmol/L glucose (P = 0.01). In contrast, at 96% theoretical Fe3+ saturation, Fe2-Tf decreased linearly with increasing glycation (r = 0.97; P = 0.008). Preincubation, independent of glycation, favored the Fe1N-Tf isoform at 64% theoretical Fe3+ saturation [27 (0.7)% vs 23 (1.1)% of the Fe1C-Tf isoform; P = 0.009]. CONCLUSIONS: Glycation impairs Fe3+ binding and affects Fe3+ -Tf isoform distribution depending on concentration. The diagnostic implications of these results need further elucidation in clinical studies.

Long-term renal function after HELLP syndrome.

This study was set up to determine the long-term (5 or more years) renal function after HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome during pregnancy and to answer the question whether long-term renal follow-up is necessary. Women with HELLP syndrome were compared with healthy control subjects who delivered their first child during the same period. There was no difference between groups for body mass index, serum and urinary creatinine levels, creatinine clearance, total urinary protein/creatinine ratio, and urinary microalbumin/creatinine ratio. Women who previously had HELLP syndrome had significantly higher diastolic and systolic blood pressures. Women with HELLP syndrome do not need continued renal follow-up, but have higher systolic and diastolic blood pressures, even 5 years after HELLP syndrome.