Glycated haemoglobin analysis

New erythrocyte parameters derived from the Coulter principle relate with red blood cell properties-A pilot study in diabetes mellitus

In routine hematological instruments, blood cells are counted and sized by monitoring the impedance signals induced during their passage through a Coulter orifice. However, only signals associated with centered paths in the aperture are considered for analysis, while the rejected measurements, caused by near-wall trajectories, can provide additional information on red blood cells (RBC), as recent publications suggest. To assess usefulness of two new parameters in describing alterations in RBC properties, we performed a pilot study to compare blood samples from patients with diabetes mellitus (DM), frequent pathological condition associated with impairment in RBC deformability, versus controls. A total of 345 blood samples were analyzed: 225 in the DM group and 120 in the control group. A diagram of [Formula: see text] and [Formula: see text], the two new parameters derived from the analysis of impedancemetry pulses, was used to compare distribution of RBC subpopulations between groups. To discriminate RBC from DM and control individuals, based on our multiparametric analysis, we built a score from variables derived from [Formula: see text] matrix which showed good performances: area under the receiving operating characteristic curve 0.948 (0.920-0.970), p<0.0001; best discriminating value: negative predictive value 94.7%, positive predictive value was 78.4%. These results seem promising to approach RBC alterations in routine laboratory practice. The related potential clinically relevant outcomes remain to be investigated.

Interference of hemoglobin variants in HbA1c quantification

Fasting blood glucose and glycated hemoglobin (HbA_1c) are routine biomarkers to screen and monitor diabetes mellitus. HbA_1c results from glycation at the N-terminus of the β globin chain of tetrameric human hemoglobin. Fasting blood glucose level varies with the nature and amount of food intake, physical exercise, etc., and, accordingly, is a short-term measure of glucose control. In contrast, HbA_1c provides an average measure of glucose control for the long-term (8-12 weeks). Unfortunately, genetic variants of hemoglobin may interfere with HbA_1c quantification using ion exchange chromatography, capillary electrophoresis, immunoassay and boronate affinity chromatography. Mass spectrometry, however, measures total glycation of hemoglobin across both α and β globin chains and correlates well with the ion exchange based method. Additionally, mass spectrometry based quantification is not impacted by the presence of genetic variants of hemoglobin and thus might be a better analytical choice for diabetes mellitus.

Dysregulated Erythroid Mg2+ Efflux in Type 2 Diabetes

Hyperglycemia is associated with decreased Mg²⁺ content in red blood cells (RBC), but mechanisms remain unclear. We characterized the regulation of Mg²⁺ efflux by glucose in ex vivo human RBC. We observed that hemoglobin A_1C (HbA_1C) values correlated with Na⁺-dependent Mg²⁺ efflux (Na⁺/Mg²⁺ exchange) and inversely correlated with cellular Mg content. Treatment of cells with 50 mM D-glucose, but not with sorbitol, lowered total cellular Mg (2.2 ± 0.1 to 2.0 ± 0.1 mM, p < 0.01) and enhanced Na⁺/Mg²⁺ exchange activity [0.60 ± 0.09 to 1.12 ± 0.09 mmol/10¹³ cell × h (flux units, FU), p < 0.05]. In contrast, incubation with selective Src family kinase inhibitors PP2 or SU6656 reduced glucose-stimulated exchange activation (p < 0.01). Na⁺/Mg²⁺ exchange activity was also higher in RBC from individuals with type 2 diabetes (T2D, 1.19 ± 0.13 FU) than from non-diabetic individuals (0.58 ± 0.05 FU, p < 0.01). Increased Na⁺/Mg²⁺ exchange activity in RBC from T2D subjects was associated with lower intracellular Mg content. Similarly increased exchange activity was evident in RBC from the diabetic db/db mouse model as compared to its non-diabetic control (p < 0.03). Extracellular exposure of intact RBC from T2D subjects to recombinant peptidyl-N-glycosidase F (PNGase F) reduced Na⁺/Mg²⁺ exchange activity from 0.98 ± 0.14 to 0.59 ± 0.13 FU (p < 0.05) and increased baseline intracellular Mg content (1.8 ± 0.1 mM) to normal values (2.1 ± 0.1 mM, p < 0.05). These data suggest that the reduced RBC Mg content of T2D RBC reflects enhanced RBC Na⁺/Mg²⁺ exchange subject to regulation by Src family kinases and by the N-glycosylation state of one or more membrane proteins. The data extend our understanding of dysregulated RBC Mg²⁺ homeostasis in T2D.

Diabetes and Ramadan: Utility of flash-glucose monitoring derived markers of glycaemic control and comparison with glycosylated haemoglobin

AIMS

Flash glucose monitoring (FGM)-derived markers of glucose control and variability and laboratory measured HbA1c among patients with diabetes on insulin in context of Ramadan fasting (RF) were examined and compared.

METHODS

FGM data on insulin-treated patients (n = 20, age 42.3 ± 11.4 years; 18 male, 2 female; 13 with type 1 and 7 with type 2 diabetes) who fasted during Ramadan were used to calculate Q-score as an indicator of glycaemia before, during and after RF. Post-hoc analysis in a group of patients (n = 12) who had HbA1c available and appropriate for these periods was performed. Other relevant data were extracted from patient records.

RESULTS

Mean glucose (9.6 ± 1.32 v 10.78 ± 1.64 mmol/l; P < 0.0001) and Q-score increased significantly with Ramadan fasting and reduced after Ramadan. Post-hoc subgroup analysis showed a significant rise in eA1c (7.2 ± 0.4%; 55.0 ± 4.4 mmol/mol v 7.7 ± 0.5%; 61.0 ± 5.5 mmol/mol) but not in laboratory HbA1c with Ramadan fasting; eA1c reduced after Ramadan (P = 0.018).

CONCLUSIONS

Ramadan fasting was associated with a deterioration in overall glucose control and time in hyperglycaemia in insulin-treated patients. FGM-derived markers are useful and a preferable alternative to HbA1c in Ramadan studies.

Nordic Seaweed and Diabetes Prevention: Exploratory Studies in KK-Ay Mice

Background: The global epidemic of type 2 diabetes (T2D) is a challenging health problem. Lifestyle changes, including nutrition therapy, areimportant for the prevention and management of T2D. Seaweeds contain several bioactive substances with potential health properties and may be a low-cost alternative functional food in the prevention of T2D. Objective: The aim of this study was to explore the preventive effects of dried Nordic seaweed species on diabetes in an animal model of T2D. Method: Fiftymale KK-Ay mice were randomly assigned to one of four diets: control diet (chow) or diets supplemented with Alaria esculenta (AE), Saccharina latissima (SL), or Palmaria palmata (PP). The effect of the interventions on the progression of T2D was monitored over 10 weeks and evaluated by circulating glucose, glycated hemoglobin (HbA1c), insulin, glucagon, and lipid levels. Results: The SL group had significantly lower bodyweight, lower HbA1c and insulin levels, as well as higher high density lipoprotein (HDL) cholesterol levels after the 10-week intervention than the control group. At the end of the study, the control group had significantly higher HbA1c (p < 0.001) than all of the seaweed groups. Conclusion: All seaweed groups improved HbA1C compared to control and Saccharinalatissima seaweed had concomitantly beneficial effects on glycemic control and lipid levels in KK-Ay diabetic mice.

The Effects of Storage and Additives on Postmortem HbA1c Measurements

HbA1c is used in forensic toxicology to identify undiagnosed diabetes mellitus (DM) and those with poor glycemic control prior to death. HbA1c is typically measured in whole blood collected in tubes containing ethylenediaminetetraacetic acid (EDTA). The effect of other additives, including sodium fluoride (NaF), is unclear. Furthermore, the assessment of short- and long-term stability of HbA1c has produced conflicting results. In this study, we collected paired postmortem blood samples in EDTA and NaF tubes (n = 142) to assess their comparability for HbA1c measurement. Stability was assessed by measuring HbA1c at baseline, 2, 3, and 4 weeks postcollection (stored at 4°C) and at 2, 4, 6, and 12 months postcollection (stored at -20°C). We found no significant difference in HbA1c between the two preservatives at any of the time points indicating NaF is a suitable preservative for HbA1c measurement. We also determined that DM status, postmortem interval, and decomposition had no effect on stability.

Continuous subcutaneous insulin infusion versus multiple daily injections of insulin for pregnant women with diabetes

BACKGROUND

Diabetes results in a rise in blood glucose above normal physiological levels; if untreated this may cause damage to many systems including the cardiovascular and renal systems. Pregnancy increases resistance to insulin action; for those women who have pre-gestational diabetes, this results in an increasing insulin requirement. There are several methods of administering insulin. Conventionally, insulin has been administered subcutaneously, formally referred to as intensive conventional treatment, but now more usually referred to as multiple daily injections (MDI). An alternative method of insulin administration is the continuous subcutaneous insulin infusion pump (CSII).

OBJECTIVES

To compare CSII with MDI of insulin for pregnant women with pre-existing and gestational diabetes.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2016) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised trials comparing CSII with MDI for pregnant women with diabetes.

DATA COLLECTION AND ANALYSIS

Three review authors independently assessed studies and two review authors extracted data. Disagreements were resolved through discussion with the third author. We assessed the quality of the evidence using the GRADE approach.

MAIN RESULTS

We included five single-centre trials (undertaken in Italy) with 153 women and 154 pregnancies in this review.There were no clear differences in the primary outcomes reported between CSII and MDI in the included trials: caesarean section (risk ratio (RR) 1.09, 95% confidence interval (CI) 0.66 to 1.77; three trials, 71 women, evidence graded very low), large-for-gestational age (RR 4.15, 95% CI 0.49 to 34.95; three trials, 73 infants; evidence graded very low), and perinatal mortality (RR 2.33, 95% CI 0.38 to 14.32; four trials, 83 infants, evidence graded very low). Other primary outcomes were not reported in these trials (hypertensive disorders of pregnancy, development of type 2 diabetes, composite outcome of serious neonatal outcomes, and neurosensory disability).There was no clear evidence of differences in the maternal secondary outcomes: maternal weight gain during pregnancy, 24 hour mean blood glucose in each trimester, mean maternal HbA1c in each trimester, maternal hypoglycaemia, and maternal hyperglycaemia. The included studies did not report several GRADE outcomes: perineal trauma, return to pre-pregnancy weight, postnatal depression, induction of labour. Many maternal secondary outcomes were also not reported.In two trials, including a total of 61 infants, CSII was associated with an increase in mean birthweight compared with MDI (mean difference (MD) 220.56 g, 95% CI -2.09 g to 443.20 g; P = 0.05). However, the large CI including anything from a small reduction to an increase in mean birthweight and the lack of a difference in macrosomia rate (RR 3.20, CI 0.14 to 72.62; two trials, 61 infants) suggests uncertainty. Large-for-gestational age (see above), andsmall-for-gestational age also suggests uncertainty of effect. No significant differences were found in: gestation at delivery, preterm birth < 37 weeks' gestation, preterm birth < 32 weeks' gestation, neonatal hypoglycaemia (evidence graded very low), respiratory distress syndrome, neonatal hyperbilirubinaemia, and fetal anomaly. There were no data reported on many important infant outcomes, including the GRADE outcomes adiposity and diabetes. There was no follow-up of infants in childhood or adulthood, so longer-term outcomes were not reported.The only outcome reported for use of health service resources wasmaternal days hospitalised, which did not show a difference between groups in the small number of women included (MD 9.40, CI -6.04 to 24.84; one trial, 10 women).The methods used by the trials were poorly reported, for example although blinding of participants and clinicians regarding intervention allocation is impossible, it is possible to blind assessors and this along with other aspects of trial methods was not reported, which means that the trials are at an unclear or high risk of bias. We do not know if the women who participated were representative, and therefore if the results can be generalised. Most GRADE outcomes were not reported. For the GRADE outcomes that were reported, our assessment was that the evidence is very low quality (caesarean section, large-for-gestational age, perinatal mortality, andneonatal hypoglycaemia). This was due to design limitations in the included trials, small sample sizes in the trials contributing data, wide CIs crossing both the line of no effect and the line of appreciable benefit and/or harm, and often few events. We are therefore uncertain whether CSII or MDI improves outcomes for pregnant women with diabetes and their infants, and the results of further studies may differ substantially from those presented in this review.

AUTHORS' CONCLUSIONS

There is no evidence to support the use of one particular form of insulin administration over another for pregnant women with diabetes. There are only a small number of trials appropriate for meta-analysis, a small number of women included and questionable generalisability of the trial population.Pump technology has progressed since these trials were undertaken. Well-designed randomised trials are required to evaluate comparisons such as patch pumps against MDI and more conventional CSII against MDI. These trials should be adequately powered to assess the effect of interventions, and report the core set of outcomes used in Cochrane reviews of diabetes in pregnancy. Trials to assess the effects of pumps on birthweight and macrosomia rates are needed. It would be beneficial for future trials to undertake longer-term follow-up of participants and their infants, assess women's preferences, and conduct an economic evaluation.

Effect of Advanced Glycation End Products on Human Thyroglobulin's Antigenicity as Identified by the Use of Sera from Patients with Hashimoto's Thyroiditis and Gestational Diabetes Mellitus

Advanced glycation end products (AGEs) are formed on proteins after exposure to high concentrations of glucose and modify protein's immunogenicity. Herein, we investigated whether the modification of thyroglobulin (Tg) by AGEs influences its antigenicity and immunogenicity. Human Tg was incubated in vitro with increasing concentrations of D-glucose-6-phosphate in order to produce Tgs with different AGE content (AGE-Tg). Native Tg and AGE-Tgs were used in ELISA to assess the serum antibody reactivity of two patient groups, pregnant women with gestational diabetes (GDM), and patients with Hashimoto's thyroiditis (HT). We produced in vitro AGE-Tg with low and high AGE content, 13 and 49 AGE units/mg Tg, respectively. All HT patients' sera presented the same antibody reactivity profile against native Tg and AGE-Tgs, indicating that the modification of Tg by AGEs did not alter its antigenicity. Similarly, the GDM patients' sera did not discriminate among the two forms of Tg, native or artificially glycated, suggesting that the modification of Tg by AGEs might not alter its immunogenicity. The modification of Tg by AGEs has no obvious effect on neither its antigenicity nor, most likely, its immunogenicity. It seems that other Tg modifications might account for the production of aTgAbs in patients with GDM.

Diagnostic accuracy of glycosylated hemoglobin in chinese patients with gestational diabetes mellitus: a meta-analysis based on 2,812 patients and 5,918 controls

BACKGROUND AND AIMS

The accuracy of glycosylated hemoglobin (HBA1c) detection for the diagnosis of gestational diabetes mellitus (GDM) has been extensively studied in the Chinese population, but the exact role of these detections remains controversial. The present meta-analysis was performed to establish the overall accuracy of HBA1c for the diagnosis of Chinese patients with GDM.

METHODS

After a systematic review of related studies, the sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and other measures about the accuracy of HBA1c in the diagnosis of GDM were pooled using random-effects models. The summary receiver operating characteristic (SROC) curve analysis was used to summarize the overall test performance.

RESULTS

Forty-one studies included 2812 Chinese patients with GDM and 5918 controls were included in our meta-analysis. The summary estimates for HBA1c in the diagnosis of GDM in the studies included were as follows: sensitivity 0.762 (95% confidence interval [CI]: 0.746-0.777), specificity 0.917 (95% CI: 0.910-0.924), PLR 8.21 (95% CI: 3.77-17.89), NLR 0.20 (95% CI: 0.09-0.44), and DOR 41.40 (95% CI: 11.47-149.38). Our data showed that the SROC curve is positioned near the desirable upper left corner of the SROC curve, while the area under curve (AUC) was 0.93 with a Q* value of 0.865.

CONCLUSIONS

Measurement of HBA1c is likely to be a useful diagnostic tool for confirming GDM. The results of HBA1c should be interpreted in parallel with clinical findings and the results of conventional tests.

The frequency of detection of unexpected diabetes mellitus during haemoglobinopathy investigations

Aims

To establish the frequency of detection of previously undiagnosed diabetes mellitus as a result of detection of an increased glycated fraction of haemoglobin during high performance liquid chromatography (HPLC) for haemoglobinopathy diagnosis.

Methods

A prospective study was carried out over a 3-month period. During that period a total of 2094 patient samples were received for haemoglobinopathy investigation and were included in the study.

Results

Fifty samples were found to have an apparent increase in the glycated haemoglobin fraction and of these 38 were found to be from patients with known diabetes. Previously undiagnosed diabetes was discovered in 11 patients and it is likely that the twelfth patient also had diabetes.

Conclusions

The detection of evidence of undiagnosed diabetes during HPLC haemoglobinopathy investigations is not rare, there being four cases per month in this study. This incidental observation should be reported to clinical staff.

Hemoglobin variant HbE found in two South Asian diabetic patients

Glycohemoglobin, also known as hemoglobin (Hb) A(1c), is a marker of long-term glycemic control in patients with diabetes. We present two South-Asian diabetic patients whose HbA(1c) peaks were not measurable using high performance liquid chromatography (HPLC). Further investigations showed that these patients were homozygous for a hemoglobin variant, HbE (beta26 Glu-->Lys). Because of the increasing numbers of immigrants in Japan, area-specific hemoglobinopathies are now encountered more frequently than before. Thus, if discrepant results are found on an HbA(1c) assay or if the HbA(1c) value cannot be measured, such patients should be screened for hemoglobinopathies and alternative measurements for monitoring diabetes should be considered.

Performance evaluation of ion exchange and affinity chromatography for HbA1c estimation in diabetic patients with HbD: a study of 129 samples

OBJECTIVES

To compare ion exchange and boronate affinity chromatography for HbA(1c) estimation in patients with type I and II diabetes having hemoglobin D.

DESIGN AND METHODS

Systems based on ion exchange and boronate affinity chromatography were evaluated and compared for their performance for HbA(1c) estimation in patients with homozygous and heterozygous D disease.

RESULTS

Boronate affinity chromatography shows least interference by HbD in heterozygous as well as homozygous diabetic patients for HbA(1c) estimation.

CONCLUSIONS

The use of boronate affinity chromatography was found to be helpful in evaluating glycemic control in diabetic subjects with HbD.

Inaccurate hemoglobin A(1C) levels in patients with type 1 diabetes and hereditary persistence of hemoglobin F

We report 2 African-American boys with type 1 diabetes and hereditary persistence of hemoglobin F. The diagnosis came to light after both patients exhibited inconsistent hemoglobin A(1C) (HbA(1C)) levels with respect to serum glucose measurements. This demonstrates the importance of frequent glucose monitoring and interpreting the HbA(1C) level in light of serum glucose measurements.

Can plasma glucose and HbA1c predict fetal growth in mothers with different glucose tolerance levels?

To assess whether HbA1c and plasma glucose predicts abnormal fetal growth, 758 pregnant women attending 5 Diabetic Centers were screened for gestational diabetes mellitus (GDM). On glucose challenge (GCT) at 24-27 weeks of gestation (g.w.), negative cases formed the normal control group (N1). Positive cases took an oral glucose tolerance test (OGTT): those found negative were classed as false positives screening test (N2); if they had an OGTT result at least as high as their normal glucose levels, they were classed as having one abnormal glucose value (OAV) at OGTT; two values as GDM. HbA1c was assayed on the day of GCT. We considered fetal macrosomia, large for gestational age (LGA), ponderal index and mean growth percentile. Mean age, pre-pregnancy BMI, fasting plasma glucose (FPG) and HbA1c were progressively higher from N1 to GDM patients. The newborn of N2 mothers were heavier than those with N1 or GDM. The mean growth percentile was significantly higher in N2 than in N1. More LGA babies were born to OAV than to N1 or N2 women. Macrosomia and ponderal index did not differ significantly in the four groups. At logistic regression only plasma glucose at GCT could predict LGA babies and a ponderal index above 2.85. At risk analysis, GDM and OAV significantly predicted LGA babies, and GDM a ponderal index >2.85. In conclusion, FPG at GCT could predict fetal overgrowth and plasma glucose >85mg/dl doubles the risk of LGA infants. HbA1c at 24-27g.w. does not predict fetal overgrowth. Mild alterations in glucose tolerance correlate with fetal overgrowth and needs monitoring and treatment.

Continuous subcutaneous insulin infusion versus multiple daily injections of insulin for pregnant women with diabetes

BACKGROUND

Diabetes causes a rise in blood glucose above normal physiological levels causing damage to many systems including the cardiovascular and renal systems. Pregnancy causes a physiological reduction in insulin action; for those women who have pre-gestational diabetes, this results in an increasing insulin requirement. There are several methods of administering insulin. Conventionally, insulin has been administered subcutaneously, formally referred to as intensive conventional treatment, but now more usually referred to as multiple daily injections (MDI). An alternative insulin administration method is the continuous subcutaneous insulin infusion pump (CSII).

OBJECTIVES

To compare continuous subcutaneous insulin infusion with MDI of insulin for pregnant women with diabetes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (November 2006).

SELECTION CRITERIA

Randomised controlled trials comparing CSII with MDI for pregnant women with diabetes.

DATA COLLECTION AND ANALYSIS

Three authors independently assessed studies and extracted data.

MAIN RESULTS

Two studies (60 women with 61 pregnancies) were included. There was a significant increase in mean birthweight associated with CSII as opposed to MDI (weighted mean difference 220.56, 95% confidence interval (CI) -2.09 to 443.20; two trials, 61 participants). However, taking into consideration the lack of significant difference in rate of macrosomia (birthweight greater than 4000 g) (relative risk (RR) 3.20, 95% CI 0.14 to 72.62; two trials, 61 participants), this is not viewed by the authors as clinically significant. No significant differences were found in any other outcomes measured, which may reflect the small number of trials suitable for meta-analysis and the small number of participants in the included studies. No significant differences were found in perinatal mortality (RR 2.00, 95% CI 0.20 to 19.91), fetal anomaly (RR 1.07, 95% CI 0.07 to 15.54), maternal hypoglycaemia (RR 3.00, 95% CI 0.35 to 25.87) or maternal hyperglycaemia (RR 7.00, 95% CI 0.39 to 125.44).

AUTHORS' CONCLUSIONS

There is a dearth of robust evidence to support the use of one particular form of insulin administration over another for pregnant women with diabetes. The data are limited because of the small number of trials appropriate for meta-analysis, small study sample size and questionable generalisability of the trial population. Conclusions cannot be made from the data available and therefore a robust randomised trial is needed. The trial should be adequately powered to assess the efficacy of continuous subcutaneous insulin infusion versus multiple daily injections in terms of appropriate outcomes for women with diabetes.

Characterization of hemoglobin Würzburg (alpha2beta2 4(A1)Thr-->Asn), a new electrophoretically silent variant, by mass spectrometry and molecular modeling studies

The first hemoglobin (Hb) variant carrying a mutation at beta4 was identified as beta4(A1)Thr-->Asn or Hb Würzburg and constituted 38% of the total hemoglobin. It showed a slightly elevated oxygen affinity and a slightly decreased cooperativity index (n50 = 2.3 versus n50 = 2.8). The analysis of the electrostatic potential showed an increased negative charge at the site of the mutation with a displacement of beta6(A3)Glu by 1.3A. The replacement of threonine by asparagine seems to stabilize the R conformation. This may explain partially both the high affinity and the reduction in cooperativity.

Importance of measuring products of non-enzymatic glycation of proteins

Non-enzymatic glycation products are a complex and heterogeneous group of compounds which accumulate in plasma and tissues in diabetes and renal failure. There is emerging evidence that these compounds may play a role in the pathogenesis of chronic complications associated with diabetes and renal failure. So measurement of the products of non-enzymatic glycation has a twofold meaning: on one hand, measurement of early glycation products can estimate the extent of exposure to glucose and the subject's previous metabolic control; on the other hand, measurement of intermediate and late products of the glycation reaction is a precious instrument in verifying the relationship between glycation products and tissue modifications. This review summarizes current knowledge about the diagnostic utility of measuring non-enzymatic glycation products.

An efficient preparation of polyanionic affinity agent and its evaluation for the measurement of glycated hemoglobin

An efficient method was developed for the preparation of polyanionic affinity agent (3), a key component in the measurement of glycated hemoglobin (GHb). Glycated hemoglobin is an important clinical marker for diagnosis of patients with diabetes and useful to monitor the management of disease. The affinity agent (3) was prepared based on coupling reaction between poly(acrylic acid) (1) and 3-aminophenylboronic acid (2) in water. The critical features of this polymeric affinity agent (3), such as size, boronic acid incorporation ratio and concentration, on the measurement of glycated hemoglobin were evaluated. It was found that the agent (3) prepared using poly(acrylic acid) (1) with 225 kDa molecular weight gave optimal GHb measurement. The performance test results demonstrated that the boronic acid incorporation ratio and concentration of affinity agent (3) play a critical role in the assay and determines the precision of glycated hemoglobin measurement.

Diabetes control and complications: the role of glycated haemoglobin, 25 years on

The long-term complications of diabetes have major consequences for individual subjects and growing healthcare delivery and cost implications for society. Evidence for the benefits of good glycaemic control, as monitored by glycated haemoglobin measurements, has been developed in the 25 years since they were introduced to the point where HbA(1c) assays play central roles in patient management, clinical guidance and audit, and clinical trial design. In this review this evidence is examined and three classes of uncertainty identified that diminish confidence in the effectiveness of these roles for HbA(1c). 1 Analytical variability between different methods for HbA(1c) has restricted the application of clinical targets and this problem has recently been addressed by reference method standardization. There are two approaches to this which result in different HbA(1c) values and this discrepancy needs to be resolved. 2 Biological variability in HbA(1c) values between individuals also restricts its predictive role when applied to populations. The correlations between HbA(1c) measurements and various components of glycaemia (overall, fasting, postprandial) are still uncertain and differences in protein glycation and de-glycation are greater between subjects than often thought. The influence of variability in erythrocyte life span is an area where research is needed, especially in diabetic subjects. 3 Clinical variability is the most important and complex area of uncertainty. A predictive link between HbA(1c) and clinical outcomes is not as clear-cut as often stated. The correlation with the development of microvascular disease is well established in Type 1 diabetes, but in Type 2 subjects (90% of those with diabetes) the evidence that HbA(1c) monitoring is of value in predicting or preventing macrovascular disease is not strong, although it is the major cause of morbidity and early death in this group. It is recommended that, as a matter of urgency, these issues be examined, particularly within the context of self-care in diabetes.

Measurement of glycated hemoglobin percentages for use in the diagnosis and monitoring of diabetes mellitus in nonhuman primates

OBJECTIVE

To identify a technique for measurement of glycated hemoglobin percentage in blood samples obtained from various species of nonhuman primates (NHPs), to determine whether these percentages varied with respect to glycemic control, and to assess whether this physiologic variable provided a suitable test for diagnosing diabetes mellitus in NHPs.

SAMPLE POPULATION

166 blood samples collected from 121 NHPs comprising 22 species from the Haplorhine and Strepsirhine suborders and including nondiabetic, treated-diabetic, and diabetic animals in 23 zoologic institutions throughout the United States.

PROCEDURE

Hemoglobin A1c percentage was measured in 154 samples by use of high-performance liquid chromatography. Total glycated hemoglobin percentage was measured in 159 samples by use of a boronate-affinity chromatographic assay. Glucose concentration was measured in 157 samples with an autochemical analyzer by use of a hexose kinase method.

RESULTS

The boronate-affinity chromatographic technique for measurement of total glycated hemoglobin percentage was the most suitable method. Nondiabetic Haplorhines had percentages higher than those in nondiabetic Strepsirhines. In Haplorhines, diabetic animals had percentages higher than those in treated-diabetic animals, which had percentages higher than those in nondiabetic animals. In Strepsirhines, this pattern was less pronounced.

CONCLUSIONS AND CLINICAL RELEVANCE

Measurement of total glycated hemoglobin percentage provides useful information for diagnosing diabetes mellitus in Haplorhines and, possibly, in Strepsirhines. Until reference ranges are established for each species, it is recommended that results for samples from NHPs without clinical signs of diabetes mellitus be compared with results of samples collected concomitantly from NHPs with clinical signs of this condition.

Evaluation of HbA1C results in an external quality assessment scheme in South Africa

BACKGROUND

Measuring HbA1c blood levels allows us to assess average glycaemia in individuals during the preceding 6-8 weeks. There is a clear association between increasing risk of complications with higher HbA1c values and a significant risk reduction of the complications with lower HbA1c values.

METHODS

The performance of South African laboratories in an External Quality Assurance scheme for HbA1c is reported.

CONCLUSIONS

A number of laboratories and methods do not meet the required analytical standards. South African laboratories should adopt measures similar to other regional and national initiatives to significantly improve laboratory performance and bring about harmonization of HbA1c assays.

Silent haemoglobin variants and determination of HbA(1c) with the HPLC Bio-Rad Variant II

AIMS

To evaluate the determination of HbA(1c) with an automated high performance liquid chromatography (HPLC) method in patients with clinically silent haemoglobin variants.

METHODS

HbA(1c) values were determined with the ion exchange HPL Bio-Rad Variant II using the high resolution beta thalassaemia programme in patients with silent haemoglobin variants, namely: Hb Graz, Hb Sherwood Forest, Hb O Padova, and Hb D.

RESULTS

All of these haemoglobin variants caused additional peaks in the chromatograms. No clinically useful HbA(1c) results were produced for patients with Hb Graz and Hb Sherwood Forest, the results for the patient with Hb D were too low, but the results for patients with Hb O Padova were acceptable.

CONCLUSIONS

The development of this automated HPLC method modification with high resolution mode aids the identification of interference caused by the described clinically silent haemoglobin variants in HbA(1c) determination.

Reference measurement systems in clinical chemistry

BACKGROUND

In clinical chemistry, traceability of measurements is of high priority.

METHODS

In this literature review, current recommendations on the process of establishing traceability (or standardization) are critically discussed.

RESULTS

Traceability is to be established to the highest international standards by a comprehensive reference measurement system. Elementary to this system are a metrological basis, a measurement unit system, i.e., the Système International d'Unités (SI), its embodiment by a material standard and a calibration hierarchy for transfer of accuracy/trueness to the manufacturer's product calibrators and routine methods. However, for analytes lacking an unequivocally recognized entity, the International Unit (IU) and International Standard (IS) concept have been developed. On this basis, the review distinguishes between traceability of SI- and IU-analytes.

CONCLUSIONS

SI-traceability, exemplified by cortisol, is straightforward. However, special attention is needed for "free analytes" and "analyte families". For traceability of IU-analytes, exemplified by hCG, the standardization process passes different phases in function of the history of the analyte (discovery, ISs, measurement by bioassays/immunoassays, complete structure elucidation). However, perspectives to the development of an SI-based reference measurement system are realistic. Last but not least, for successful global implementation of the standardization process, consensus of all major players in the field will be required.

Effect of HbE and HbH on HbA1C level by ionic exchange HPLC comparing to immunoturbidimetry

BACKGROUND

The hemoglobin (Hb)A1C level is widely used to monitor diabetes mellitus patients. The N-terminal amino acid valine of its beta chain is glycated. The assay of HbA1C is based on differences in the charge, chemical and structural properties of the protein.

METHODS

There are fully automated instruments available in clinical chemistry laboratory to assay HbA1C level. The effect of hemoglobinopathies was studied between an ionic exchange high-pressure liquid chromatography (HPLC) (Bio-Rad Laboratories, USA) and immunoturbidimetry (BM/Hitachi 912 with Roche HBA1CII, Germany-Japan) assay. The influence of high level HbF relative to the HbA1C level by ionic exchange HPLC is known. The effect of HbE and HbH to the HbA1C level by ionic exchange HPLC comparing to immunoturbimetry was examined. The evaluation was performed on 34 normal controls (A2A), 17 beta thalassemia traits (A2 upward arrow A), 36 HbE heterozygotes (EA), 37 HbE homozygotes (EE), 36 beta thalassemia/HbE (EF/EFA), 11 EABart's diseases (EABart's), 34 Hb H diseases (A2/CSAH) and 13 cord blood samples (FA).

CONCLUSIONS

Hemoglobinopathies can impact on the assay of HbA1C level such as HbE and HbH to ionic exchange HPLC. Although not studied as yet, this effect may influence the other methods such as affinity chromatography.

Hemoglobin variants and determination of glycated hemoglobin (HbA1c)

Measurement of glycated hemoglobin in diabetic patients is an established procedure for evaluating long-term control of diabetes. The Diabetes Control and Complications Trial (DCCT), as well as the United Kingdom Prospective Diabetes Study (UKPDS), confirmed the direct relationship between the degree of glycemic control as estimated by glycohemoglobin (GHb) determinations and the development and progression of long-term complications in diabetic patients. Samples with known interferences of HbA(1c) determination as hemoglobinopathies are specifically excluded from certification testing and there are no guidelines or requirements for comparability of samples containing hemoglobin (Hb) variants. This paper reviews the interference of Hb variants on determination methods of glycated hemoglobin as they result in false HbA(1c) results.

Long-Term Evaluation of Electrospray Ionization Mass Spectrometric Analysis of Glycated Hemoglobin

Background: Electrospray ionization mass spectrometry (ESIMS) has been successfully applied to the identification of hemoglobin (Hb) variants and the presence of glucose adducts (mass difference of 162 Da) on the separate Hb α and β chains. To establish the potential of ESIMS as a routine and/or a reference method for the quantification of glycohemoglobin (HbA1c), we carried out a detailed evaluation over a 4-month period in a routine laboratory environment.

Methods: We optimized a procedure using ESIMS suitable for the routine quantitative analysis of HbA1c. We determined reliability and reproducibility over 4 months and assessed the potential for automated sample injection. We then compared values of 1022 blood samples from diabetic patients with a routine HPLC-based ion-exchange procedure (HA-8140; Menarini).

Results: Results of HbA1c measurement by ESIMS were available within 3 min. The analytical imprecision (CV) was 1.6–5.0% for both manual and automated injections. Data collection over the m/z 980-1400 range confirmed lower glycation of the α chain relative to the β chain (0.66:1). Only one glycation was observed per globin chain. The overall glycohemoglobin (i.e., the average of α- and β-chain glycations) measured by ESIMS (x) on 1022 blood samples was lower than by HPLC (y): y = 1.0432x + 0.4815. However, the β-chain glycation measured by ESIMS was up to 20% higher than the value measured by ion-exchange HPLC and showed a close conformity, particularly at 5–10% HbA1c, with the ion-exchange Diabetes Control and Complications Trial (DCCT)-corrected and the United Kingdom National External Quality Assessment Scheme DCCT mean return values.

Conclusions: ESIMS provides a precise measurement of HbA1c and, in particular, glycation of the β chain. The method is robust and could be proposed as a procedure to substantiate HbA1c measurement and/or calibration.

Measurement of glycated haemoglobin in whole blood by a novel fluorescence quenching assay

We describe a method for the specific measurement of glycated Hb (GHb) by fluorescence quenching. Whole blood is added to lysing solution, then the lysate is mixed with eosin-boronic acid solution and reacted for at least 5 min at room temperature. The quenching of the fluorescence of the eosin-boronic acid solution is proportional to the concentration of GHb present. Total Hb concentration was measured by absorbance and the GHb expressed as a percentage of the total Hb. Comparison with a commercial high-performance liquid chromatography (HPLC) system for HbA1c showed: %GHb=1.30 (SD 0.04) %HbA1c + 1.36 (SD 0.30), S(y/x) 0.803, n=95, r=0.965 (SD=standard deviation). Intra-assay coefficients of variation were <2.5% (for GHb concentrations in the range 6-20%) and inter-assay coefficients of variation were <4.1% (10 assays on six samples with GHb concentrations in the range 6-20%). Linearity of response was demonstrated by dilution. The effect of adding exogenous glucose, bilirubin and triglycerides was tested on samples with low, medium and high GHb concentrations. No significant interference was found. Variation of haematocrit over the range 0.4-0.6 also had no significant effect on percentage GHb. Preliminary results with samples containing variant Hb (HbAS and HbAC) indicated good agreement with HPLC for these samples also.

Evaluation of a fully automated high-performance liquid chromatography assay for hemoglobin A1c

INTRODUCTION

Measurement of hemoglobin A1c (HbA1c) is used as an objective measure of long-term blood glucose control in diabetic patients. Recent improvements in automation combined with new recommendations for precision and accuracy have caused us to reevaluate our methods for measuring HbA1c.

OBJECTIVE

We evaluated a newly automated high-performance liquid chromatography (HPLC) instrument for measurement of HbA1c (Tosoh A1c 2.2 Plus Glycohemoglobin Analyzer, Tosoh Medics, Foster City, Calif) and compared the results obtained by HPLC to those obtained with an immunoassay (Hitachi 911, Boehringer Mannheim Corporation, Indianapolis, Ind).

RESULTS

The Tosoh analyzer was found to be linear in a range of 5.3% to 17% and had a throughput of 20 samples per hour. HbA1c results for 102 patient samples by the 2 techniques showed good correlation, with a slope of 0.87 and an intercept at 1.27% +/- 0.15%. Both the total and within-run coefficients of variation were consistently lower for the HPLC method compared with the immunoassay method. The HPLC method produces a chromatogram that shows the different hemoglobin fractions, allowing identification of abnormal hemoglobin variants. In heterozygous individuals, HbA1c measurements are made with no interference from the hemoglobin variant. In the case of homozygous or doubly heterozygous hemoglobin variants, the Tosoh HPLC identifies the hemoglobin variants as such and correctly does not report a HbA1c value in the presence of a markedly decreased amount of hemoglobin A.

CONCLUSIONS

The Tosoh HPLC provides adequate throughput and improved precision, and the method is traceable to the Diabetes Control and Complications Trial.

Direct evaluation of glycated and glyco-oxidized globins by matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been applied to achieve a qualitative and quantitative evaluation of glycated globins on a wide number of healthy and diabetic subjects. The method allowed us to establish that both alpha- and beta-globins are glycated and that, in addition to simply glycated products, other species are detected. Investigations by different sample treatments and by analysis of the glycated beta-globin fraction obtained by preparative chromatography indicated that these species correspond to glyco-oxidized globins. Consequently MALDI-MS can be validly employed to evaluate not only the glycation level, but also the degree of oxidative stress. The percentages of glycated and glycooxidized species were calculated from the related MALDI spectra by the measurement of the related peak areas, without any other treatment of data. A linear relationship between HbA1c values and the total percentage of glycated and glyco-oxidized globins has been found, and its slope (< 1) has been rationalized by the uncorrected evaluation of glycated globins content in the standard samples employed for HbA1c measurements.

Non-separation assay for glycohemoglobin

The determination of glycohemoglobin [HbA1c, HbA1, or total glycohemoglobin (GHb)] has become an established procedure in the management of diabetes mellitus. Here, we describe the development of a simple, fluorescence, non-separation assay for the percentage of GHb (%GHb). The fluorescence of an eosin-boronic acid derivative when it was mixed with hemolysates of unwashed erythrocytes was quenched in proportion to the percentage of glycohemoglobin. Measurement of the fluorescence intensity gave an estimate of GHb in the sample, and measurement of light absorbance gave an estimate of total hemoglobin. A combination of the two measurements gave the assay response. Comparison with HPLC (Menarini-Arkray HA-8140 fully automated analyzer) for the percentage of HbA1 (%HbA1) gave %GHb(NETRIA) = 1.1(SD ±0.03)%HbA1 +0.6(SD ±0.3), Sy‖x = 0.821, r = 0.972, n = 80; comparison for HbA1c gave %GHb(NETRIA) = 1.3(SD ±0.04)%HbA1c + 1.8(SD ±0.3), Sy‖x = 0.813, r = 0.973, n = 80. Precision, estimated as the percentage of the CV of the %GHb assay results, was &lt;2% (intraassay, range 5–22% GHb) and &lt;4.2% (interassay, range 4–16% GHb). Dilution of a high-percentage GHb sample lysate showed that the assay was linear, and addition of glucose (60 mmol/L), bilirubin (250 μmol/L), and triglycerides (14 mmol/L) to low, medium, and high %GHb samples showed no clinical interference in assay results.

Monitoring diabetic control in developing countries: a review of glycated haemoglobin and fructosamine assays

Measurement of glycated proteins, especially haemoglobins, is now a routine procedure for monitoring previous glycaemic control in diabetic patients in the developed world. Until recently, however, the assays were sophisticated and costly and, therefore, were only rarely used in developing countries. With easier and cheaper tests now available, the measurement of glycaemic control could be also introduced into regional hospitals in developing countries. This paper reviews feasible methods for clinical laboratories with limited resources. Recent experiences from African countries are included.