Effect of aging on A1C levels in individuals without diabetes: evidence from the Framingham Offspring Study and the National Health and Nutrition Examination Survey 2001-2004

The potential impact of using glycated haemoglobin as the preferred diagnostic tool for detecting Type 2 diabetes mellitus

AIMS

There are calls to simplify the diagnosis of Type 2 diabetes mellitus (T2DM) to reduce the burden of undiagnosed disease. Glycated haemoglobin (HbA(1c)) is therefore being considered as a preferred diagnostic tool to replace the need for an oral glucose tolerance test (OGTT), considered by many as cumbersome and inconvenient. The aim of this study was to examine the potential impact of the preferred use of HbA(1c) as a diagnostic tool on the prevalence and phenotype of T2DM.

METHODS

Analysis of the Leicester Ethnic Atherosclerosis and Diabetes Risk (LEADER) cohort for previously undiagnosed individuals between 40 and 75 years of age who had OGTT, repeated if within the diabetes range, and HbA(1c) results. We compared the prevalence and phenotype of subjects with T2DM based on either HbA(1c)> or =6.5% or OGTT using 1999 World Health Organization criteria.

RESULTS

From the total population of 8696, we detected 291 (3.3%) with T2DM from using an OGTT, and 502 (5.8%) had HbA(1c)> or =6.5%. Of those diagnosed with T2DM by OGTT, 93 (1.2%) had HbA(1c) <6.5% and therefore would not have been classified as having T2DM using proposed criteria. Using HbA(1c) criteria resulted in 304 (3.5%) additional cases of T2DM, approximately doubling the prevalence. Of these 304 additional people, 172 (56.7%) had impaired glucose tolerance/impaired fasting glycaemia according to 1999 World Health Organization criteria. Using HbA(1c) criteria there was an increase of 2.2- and 1.4-fold in south Asians and white Europeans detected, respectively.

CONCLUSIONS

Within this multi-ethnic cohort, we found that introducing HbA(1c)> or =6.5% as the preferred diagnostic test to diagnose T2DM significantly increased numbers detected with T2DM; however, some people were no longer detected as having T2DM.

Markedly low hemoglobin A1c in a patient with an unusual presentation of beta-thalassemia minor

OBJECTIVE

To describe very low hemoglobin A1c levels in a patient with type 2 diabetes mellitus and an unusual presentation of beta-thalassemia minor.

METHODS

We present the clinical and laboratory findings of the study patient.

RESULTS

A 64-year-old African American man with type 2 diabetes mellitus was referred to the endocrinology clinic with a hemoglobin A1c level of 1.6% despite elevated blood glucose concentrations. A red blood cell survival study with chromium-51 revealed that he had a reduced erythrocyte life span less than 25% of normal. He also had a markedly elevated reticulocyte count ranging from 236 to 534 x 10(3)/microL (reference range, 25-75 x 10(3)/microL). The laboratory findings, which are not characteristic of beta-thalassemia minor, could be the cause of the markedly low hemoglobin A1c in this patient.

CONCLUSIONS

Although rare, when associated with marked erythrocyte turnover, beta-thalassemia minor can lead to a severe reduction in HbA1c levels. In this scenario, glycemic control is best assessed by measuring fructosamine.

Prevalence of diabetes and high risk for diabetes using A1C criteria in the U.S. population in 1988-2006

OBJECTIVE We examined prevalences of previously diagnosed diabetes and undiagnosed diabetes and high risk for diabetes using recently suggested A1C criteria in the U.S. during 2003-2006. We compared these prevalences to those in earlier surveys and those using glucose criteria. RESEARCH DESIGN AND METHODS In 2003-2006, the National Health and Nutrition Examination Survey included a probability sample of 14,611 individuals aged > or =12 years. Participants were classified on glycemic status by interview for diagnosed diabetes and by A1C, fasting, and 2-h glucose challenge values measured in subsamples. RESULTS Using A1C criteria, the crude prevalence of total diabetes in adults aged > or =20 years was 9.6% (20.4 million), of which 19.0% was undiagnosed (7.8% diagnosed, 1.8% undiagnosed using A1C > or =6.5%). Another 3.5% of adults (7.4 million) were at high risk for diabetes (A1C 6.0 to <6.5%). Prevalences were disproportionately high in the elderly. Age-/sex-standardized prevalence was more than two times higher in non-Hispanic blacks and Mexican Americans versus non-Hispanic whites for diagnosed, undiagnosed, and total diabetes (P < 0.003); standardized prevalence at high risk for diabetes was more than two times higher in non-Hispanic blacks versus non-Hispanic whites and Mexican Americans (P < 0.00001). Since 1988-1994, diagnosed diabetes generally increased, while the percent of diabetes that was undiagnosed and the percent at high risk of diabetes generally decreased. Using A1C criteria, prevalences of undiagnosed diabetes and high risk of diabetes were one-third that and one-tenth that, respectively, using glucose criteria. CONCLUSIONS Although A1C detects much lower prevalences than glucose criteria, hyperglycemic conditions remain high in the U.S., and elderly and minority groups are disproportionately affected.

The role of mitochondria in the pathophysiology of skeletal muscle insulin resistance

Multiple organs contribute to the development of peripheral insulin resistance, with the major contributors being skeletal muscle, liver, and adipose tissue. Because insulin resistance usually precedes the development of type 2 diabetes mellitus (T2DM) by many years, understanding the pathophysiology of insulin resistance should enable development of therapeutic strategies to prevent disease progression. Some subjects with mitochondrial genomic variants/defects and a subset of lean individuals with hereditary predisposition to T2DM exhibit skeletal muscle mitochondrial dysfunction early in the course of insulin resistance. In contrast, in the majority of subjects with T2DM the plurality of evidence implicates skeletal muscle mitochondrial dysfunction as a consequence of perturbations associated with T2DM, and these mitochondrial deficits then contribute to subsequent disease progression. We review the affirmative and contrarian data regarding skeletal muscle mitochondrial biology in the pathogenesis of insulin resistance and explore potential therapeutic options to intrinsically modulate mitochondria as a strategy to combat insulin resistance. Furthermore, an overview of restricted molecular manipulations of skeletal muscle metabolic and mitochondrial biology offers insight into the mitochondrial role in metabolic substrate partitioning and in promoting innate adaptive and maladaptive responses that collectively regulate peripheral insulin sensitivity. We conclude that skeletal muscle mitochondrial dysfunction is not generally a major initiator of the pathophysiology of insulin resistance, although its dysfunction is integral to this pathophysiology and it remains an intriguing target to reverse/delay the progressive perturbations synonymous with T2DM.

Effect of age and race/ethnicity on HbA1c levels in people without known diabetes mellitus: implications for the diagnosis of diabetes

AIMS

To determine if age and race/ethnicity affect HbA1c levels independent of glycemia.

METHODS

We analyzed 2712 individuals from the NHANES III population 40-74 years old without diabetes history.

RESULTS

HbA1c levels increased by 0.10% per decade in people with NGT and 0.07% in those with IFG and/or IGT, independent of fasting and 2-h glucose on OGTT's. Compared to non-Hispanic whites, HbA1c levels increased by 0.12% (NGT) and 0.10% (IFG/IGT) in Mexican-Americans and 0.21% (NGT) and 0.35% (IFG/IGT) in non-Hispanic blacks, independent of glycemia. At HbA1c levels of >or=6.5%, >or=7.0% and 6.5-6.9%, diabetes diagnosed by current FPG/OGTT criteria occurred in 82%, 94% and 65%, respectively. In non-Hispanic blacks with HbA1c levels of 6.5-6.9%, 68% of those 40-74 years old and 87% of those over 64 years old would not have diabetes by FPG/OGTT criteria. Over 90% of all race/ethnicity groups would have diabetes with HbA1c levels >or=7.0%.

CONCLUSIONS

Because many people, especially older non-Hispanic blacks, with HbA1c levels of 6.5-6.9% would not have diabetes by current FPG/OGTT criteria and clinical retinopathy and nephropathy are very unusual in patients whose HbA1c levels are kept <7.0%; we recommend an HbA1c level of >or=7.0% to diagnose diabetes.

Relationship between A1C and glucose levels in the general Dutch population: the new Hoorn study

OBJECTIVE

To investigate the relationship among A1C, fasting plasma glucose (FPG), and 2-h postload plasma glucose in the Dutch general population and to evaluate the results of using A1C for screening and diagnosis of diabetes.

RESEARCH DESIGN AND METHODS

In 2006-2007, 2,753 participants of the New Hoorn Study, aged 40-65 years, who were randomly selected from the population of Hoorn, the Netherlands, underwent an oral glucose tolerance test (OGTT). Glucose status (normal glucose metabolism [NGM], intermediate hyperglycemia, newly diagnosed diabetes, and known diabetes) was defined by the 2006 World Health Organization criteria. Spearman correlations were used to investigate the agreement between markers of hyperglycemia, and a receiver operating characteristic (ROC) curve was calculated to evaluate the use of A1C to identify newly diagnosed diabetes.

RESULTS

In the total population, the correlations between fasting plasma glucose and A1C and between 2-h postload plasma glucose and A1C were 0.46 and 0.33, respectively. In patients with known diabetes, these correlations were 0.71 and 0.79. An A1C level of > or =5.8%, representing 12% of the population, had the highest combination of sensitivity (72%) and specificity (91%) for identifying newly diagnosed diabetes. This cutoff point would identify 72% of the patients with newly diagnosed diabetes and include 30% of the individuals with intermediate hyperglycemia.

CONCLUSIONS

In patients with known diabetes, correlations between glucose and A1C are strong; however, moderate correlations were found in the general population. In addition, based on the diagnostic properties of A1C defined by ROC curve analysis, the advantage of A1C compared with OGTT for the diagnosis of diabetes is limited.

Clinically significant disagreement between mean blood glucose and estimated average glucose in two populations: implications for diabetes management

BACKGROUND

Hemoglobin A1c (HbA1c) is highly correlated with mean blood glucose (MBG) levels and widely used in assessment of diabetes therapy. It has been proposed to report HbA1c in terms of an estimated average glucose (eAG) derived from the population regression of MBG on HbA1c. Pertinent to the clinical utility of eAG would be the degree of agreement between eAG and MBG estimated from multiple sampled glucose measurements over time.

METHODS

We examined agreement between eAG and MBG by Bland-Altman analysis from two different populations of type 1 diabetes patients: 150 children at our clinic in New Orleans and publicly available data from 1440 participants in the Diabetes Control and Complications Trial (DCCT). In New Orleans, MBG was derived from the mean of each patient's self-monitored glucose records over the 3 months before the HbA1c was obtained at the patient's clinic visit. Hemoglobin A1c was traceable to the DCCT. In DCCT participants, MBG was calculated from the patient's seven-sample glucose profile set submitted during each quarterly visit. Estimated average glucose was calculated from each individual's HbA1c using a previously reported regression equation of MBG versus HbA1c, eAG = (HbA1c * 28.7) - 47.7, derived from a continuous glucose monitoring protocol over a 12-week period.

RESULTS

The analysis showed that there is frequent and clinically significant disagreement between MBG and eAG. Estimated average glucose over or under estimated MBG by 28.7 mg/dl or greater (HbA1c difference of 1% or greater) in approximately 33% of patients from both populations. The eAG overestimation of MBG was highest at lower MBG. The difference between eAG and MBG was skewed upward with increasing mean of eAG and MBG in the DCCT.

CONCLUSIONS

Frequent discordance between eAG and MBG in clinical practice will likely be confusing to patients and clinicians. In patients where eAG overestimates MBG, intensive management based on eAG alone will likely lead to greater frequency of hypoglycemic episodes. To overcome these limitations of eAG, a customized assessment of HbA1c with respect to a patient's MBG should be performed using directly monitored patient glucose levels over time.

A Randomized Comparison of the Terms Estimated Average Glucose Versus Hemoglobin A1C

Purpose

The purpose of this study was to evaluate the hypothesis that using estimated average glucose (eAG) while instructing patients yields better knowledge retention than using the term hemoglobin A1C (A1C).

Methods

Patients with diabetes who had poor baseline understanding of A1C (determined by a 4-question survey) were randomized into 1 of 2 groups: A1C or eAG. Depending on randomization, providers discussed patients' current status and personal targets for glycemic control using either the term A1C or estimated average glucose. Patients had a telephone survey 3—4 weeks later, assessing change in knowledge of glycemic control.

Results

The 80 participants who completed follow-up had similar baseline characteristics, including poor understanding of A1C and poor recall of previous A1C values. At the 3—4 week follow-up, average score for each survey question improved significantly in both groups, with mean composite score increasing in the A1C group by 32% and in the eAG group by 33%. There was no suggestion of a difference in degree of improvement between groups.

Conclusions

Patients previously unfamiliar with the meaning of A1C, using either term (A1C or eAG) resulted in an equal improvement in knowledge. Within this study, eAG was not a more understandable term, or an easier concept for patients to remember. Further research is needed to test whether use of the term A1C should be replaced by eAG.

Influence of variables on hemoglobin A1c values and nonheterogeneity of hemoglobin A1c reference ranges

INTRODUCTION

Hemoglobin A1c (HbA1c) values are influenced by analytical interferences such as HbF and hemoglobin variants and clinical factors such as increased red cell turnover. Although less well-known, demographic factors such as race, age, and sex also influence HbA1c values. The HbA1c reference range should be homogenous in the United States based on the use of National Glycohemoglobin Standardization Program certified methods and the recommendations in the National Academy of Clinical Biochemistry guidelines.

METHODS

Data on age, race, sex, HbA1c, and glucose values were extracted from the National Health and Nutrition Examination study for a 3 year period. A search for reference range data for laboratories in the United States was performed using the Google search engine.

RESULTS

Extracted data agree with published data on the influence of age, sex, and smoking status on HbA1c values. There is substantial heterogeneity in HbA1c reference ranges in laboratories in the United States.

CONCLUSION

Age, sex, and smoking status influence HbA1c values. Despite standardization of HbA1c methods and published recommendations, there is wide heterogeneity in HbA1c reference ranges in the United States.

Biologic variability in plasma glucose, hemoglobin A1c, and advanced glycation end products associated with diabetes complications

Plasma glucose plays a key role in the complications of diabetes mellitus. Hemoglobin A1c (HbA1c) and circulating concentrations of advanced glycation end products (AGEs) are central to diabetes clinical care and pathophysiology. However, there is evidence for variation between individuals in the relationship of plasma glucose to both these measures and to specific complications. The glycation gap (GG) and hemoglobin glycation index represent tools for quantitating the variability in the relationship between plasma glucose and HbA1c useful for identification of underlying mechanisms. Recent evidence demonstrates the heritability of HbA1c, the GG, and AGEs, yet not of glycated serum proteins. There has been tremendous effort devoted to identifying the heritable basis of types 1 and 2 diabetes; however, studies on the heritable contributors to these mediators of glucose effect on complications are only beginning. New evidence for normal biologic variation in the distribution of glucose into the red blood cell (RBC) intracellular compartment and RBC lifespan in people with and without diabetes represent candidates for heritable mechanisms and contributors to the rise in HbA1c with age. Taken as a whole, genetic and mechanistic evidence suggests new potential targets for complications prevention and improvement in complications risk estimation. These observations could help tilt the risk-benefit balance in glycemic control toward a more beneficial outcome.

The clinical use of hemoglobin A1c

Hemoglobin A1c (HbA1c) has been accepted as an index of glycemic control since the mid-1970s and is the best marker for diabetic microvascular complications. Clinically, it is now used to assess glycemic control in people with diabetes. Assays are most reliable when certified by the National Hemoglobin Standardization Program but are subject to confounders and effect modifiers, particularly in the setting of hematologic abnormalities. Other measures of chronic glycemic control-fructosamine and 1,5-anhydroglucitol-are far less widely used. The relationship of HbA1c to average blood glucose was intensively studied recently, and it has been proposed that this conversion can be used to report an "estimated average glucose, eAG" in milligrams/deciliter or millimolar units rather than as per cent glycated hemoglobin. Finally, HbA1c has been proposed as a useful method of screening for and diagnosing diabetes.

HbA1c: how do we measure it and what does it mean?

PURPOSE OF REVIEW

Description of recent developments in the standardization of HbA1c measurement and interpretation of HbA1c results.

RECENT FINDINGS

HbA1c is extensively used in the management of patients with diabetes. The two major schemes to standardize HbA1c produce values that differ substantially. A prospective, multinational study revealed a linear correlation between HbA1c and average blood glucose. Some, but not all, assay methods are able to accurately measure HbA1c in individuals with common hemoglobin variants.

SUMMARY

Progress in standardization of methods for HbA1c measurement has significantly reduced variation among different methods. The improved accuracy could allow HbA1c to be used for screening and diagnosis of diabetes. A consensus document recommends that HbA1c be reported in both NGSP (%) and IFCC (mmol/mol) units. HbA1c results can be translated into estimated average glucose (eAG), which could be reported in addition to HbA1c.