Differences in A1C by race and ethnicity among patients with impaired glucose tolerance in the Diabetes Prevention Program

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.

Partners reducing effects of diabetes (PREDICT): a diabetes prevention physical activity and dietary intervention through African-American churches

Type 2 diabetes is epidemic in the United States with greater incidence rates in African-American communities. Lifestyle interventions during the phase of insulin resistance mitigate cardiovascular risk and prevent diabetes. The primary aim of this study is to test the impact of a Community Health Advisor (CHA)-based diabetes prevention controlled intervention in urban African-American communities. In this controlled trial, church congregants in New Haven, CT, receiving a 1-year CHA-led diabetes prevention intervention were compared with church congregants in Bridgeport, CT, who did not receive an intervention. Outcome measures included physical activity, dietary pattern, anthropometric measure, social support, diabetes knowledge, nutrition and exercise self-efficacy. The results indicate that at the end of the 1-year intervention period, there were no significant differences observed between intervention and control groups. Possible explanations for the lack of change include difficulty in engaging the CHAs, variability in the CHA-led interventions, baseline discrepancies between the two sites which could not be fully controlled and loss to follow-up. The results indicate important obstacles which impeded the successful implementation of this intervention and lessons learned for future interventions.

Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults

BACKGROUND

Fasting glucose is the standard measure used to diagnose diabetes in the United States. Recently, glycated hemoglobin was also recommended for this purpose.

METHODS

We compared the prognostic value of glycated hemoglobin and fasting glucose for identifying adults at risk for diabetes or cardiovascular disease. We measured glycated hemoglobin in whole-blood samples from 11,092 black or white adults who did not have a history of diabetes or cardiovascular disease and who attended the second visit (occurring in the 1990-1992 period) of the Atherosclerosis Risk in Communities (ARIC) study.

RESULTS

The glycated hemoglobin value at baseline was associated with newly diagnosed diabetes and cardiovascular outcomes. For glycated hemoglobin values of less than 5.0%, 5.0 to less than 5.5%, 5.5 to less than 6.0%, 6.0 to less than 6.5%, and 6.5% or greater, the multivariable-adjusted hazard ratios (with 95% confidence intervals) for diagnosed diabetes were 0.52 (0.40 to 0.69), 1.00 (reference), 1.86 (1.67 to 2.08), 4.48 (3.92 to 5.13), and 16.47 (14.22 to 19.08), respectively. For coronary heart disease, the hazard ratios were 0.96 (0.74 to 1.24), 1.00 (reference), 1.23 (1.07 to 1.41), 1.78 (1.48 to 2.15), and 1.95 (1.53 to 2.48), respectively. The hazard ratios for stroke were similar. In contrast, glycated hemoglobin and death from any cause were found to have a J-shaped association curve. All these associations remained significant after adjustment for the baseline fasting glucose level. The association between the fasting glucose levels and the risk of cardiovascular disease or death from any cause was not significant in models with adjustment for all covariates as well as glycated hemoglobin. For coronary heart disease, measures of risk discrimination showed significant improvement when glycated hemoglobin was added to models including fasting glucose.

CONCLUSIONS

In this community-based population of nondiabetic adults, glycated hemoglobin was similarly associated with a risk of diabetes and more strongly associated with risks of cardiovascular disease and death from any cause as compared with fasting glucose. These data add to the evidence supporting the use of glycated hemoglobin as a diagnostic test for diabetes.

Moving to an A1C-based diagnosis of diabetes has a different impact on prevalence in different ethnic groups

OBJECTIVE To compare screen-detected diabetes prevalence and the degree of diagnostic agreement by ethnicity with the current oral glucose tolerance test (OGTT)-based and newly proposed A1C-based diagnostic criteria. RESEARCH DESIGN AND METHODS Six studies (1999-2009) from Denmark, the U.K., Australia, Greenland, Kenya, and India were tested for the probability of an A1C > or =6.5% among diabetic case subjects based on an OGTT. The difference in probability between centers was analyzed by logistic regression adjusting for relevant confounders. RESULTS Diabetes prevalence was lower with the A1C-based diagnostic criteria in four of six studies. The probability of an A1C > or =6.5% among OGTT-diagnosed case subjects ranged widely (17.0-78.0%) by study center. Differences in diagnostic agreement between ethnic subgroups in the U.K. study were of the same magnitude as between-country comparisons. CONCLUSIONS A shift to an A1C-based diagnosis for diabetes will have substantially different consequences for diabetes prevalence across ethnic groups and populations.

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.

A1C cut points to define various glucose intolerance groups in Asian Indians

OBJECTIVE To determine A1C cut points for glucose intolerance in Asian Indians. RESEARCH DESIGN AND METHODS A total of 2,188 participants without known diabetes were randomly selected from the Chennai Urban Rural Epidemiology Study. All had fasting plasma glucose (FPG) and 2-h postload plasma glucose measurements after a 75-g load and were classified as having impaired fasting glucose (IFG) (American Diabetes Association [ADA] criteria, FPG > or =5.5 and <7 mmol/l, and World Health Organization [WHO] criteria, FPG > or =6.1 and <7 mmol/l), impaired glucose tolerance (IGT) (2-h postload plasma glucose > or =7.8 and <11.1 mmol/l), or diabetes (FPG > or =7 mmol/l and/or 2-h postload plasma glucose > or =11.1 mmol/l). A1C was measured using the Bio-Rad Variant machine. Based on receiver operating characteristic curves, optimum sensitivity and specificity were derived for defining A1C cut points for diabetes, IGT, and IFG. RESULTS Mean +/- SD values of A1C among subjects with normal glucose tolerance, IGT, and diabetes were 5.5 +/- 0.4, 5.9 +/- 0.6, and 8.3 +/- 2.0%, respectively (P(trend) < 0.001) with considerable overlap. To identify diabetes based on 2-h postload plasma glucose, the A1C cut point of 6.1% had an area under the curve (AUC) of 0.941 with 88.0% sensitivity and 87.9% specificity. When diabetes was defined as FPG > or =7.0 mmol/l, the A1C cut point was 6.4% (AUC = 0.966, sensitivity 93.3%, and specificity 92.3%). For IGT, AUC = 0.708; for IFG, AUC = 0.632 (WHO criteria) and 0.708 (ADA criteria), and the A1C cut point was 5.6%. CONCLUSIONS In Asian Indians, A1C cut points of 6.1 and 6.4% defined diabetes by 2-h postload plasma glucose or FPG criteria, respectively. A value of 5.6% optimally identified IGT or IFG but was <70% accurate.

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.

Comparison of A1C and fasting glucose criteria to diagnose diabetes among U.S. adults

OBJECTIVE

To compare A1C and fasting glucose for the diagnosis of diabetes among U.S. adults.

RESEARCH DESIGN AND METHODS

This study included 6,890 adults (> or =20 years of age) from the 1999-2006 National Health and Nutrition Examination Survey without a self-reported history of diabetes who had fasted > or =9 h. A1C > or =6.5% and fasting glucose > or =126 mg/dl were used, separately, to define diabetes.

RESULTS

Overall, 1.8% of U.S. adults had A1C > or =6.5% and fasting glucose > or =126 mg/dl, 0.5% had A1C > or =6.5% and fasting glucose <126 mg/dl, and 1.8% had A1C <6.5% and fasting glucose > or =126 mg/dl. Compared with individuals with A1C <6.5% and fasting glucose > or =126 mg/dl, individuals with A1C > or =6.5% and fasting glucose <126 mg/dl were younger, more likely to be non-Hispanic black, had lower Hb levels, and had higher C-reactive protein.

CONCLUSIONS

A1C > or =6.5% demonstrates reasonable agreement with fasting glucose for diagnosing diabetes among U.S. adults.

The potential of cinnamon to reduce blood glucose levels in patients with type 2 diabetes and insulin resistance

AIM

Cinnamon has a long history as an antidiabetic spice, but trials involving cinnamon supplementation have produced contrasting results. The aim of this review was to examine the results of randomized controlled clinical trials of cinnamon and evaluate the therapeutic potential amongst patients with diabetes and insulin-resistant patients, particularly the ability to reduce blood glucose levels and inhibit protein glycation.

METHODS

A systematic electronic literature search using the medical subject headings 'cinnamon' and 'blood glucose' was carried out to include randomized, placebo-controlled in vivo clinical trials using Cinnamomum verum or Cinnamomum cassia conducted between January 2003 and July 2008.

RESULTS

Five type 2 diabetic and three non-diabetic studies (total N = 311) were eligible. Two of the diabetic studies illustrated significant fasting blood glucose (FBG) reductions of 18-29% and 10.3% (p < 0.05), supported by one non-diabetic trial reporting an 8.4% FBG reduction (p < 0.01) vs. placebo, and another illustrating significant reductions in glucose response using oral glucose tolerance tests (p < 0.05). Three diabetic studies reported no significant results.

CONCLUSIONS

Whilst definitive conclusions cannot be drawn regarding the use of cinnamon as an antidiabetic therapy, it does possess antihyperglycaemic properties and potential to reduce postprandial blood glucose levels. Further research is required to confirm a possible correlation between baseline FBG and blood glucose reduction and to assess the potential to reduce pathogenic diabetic complications with cinnamon supplementation.

Ethnicity, race, and clinically significant macular edema in the Veterans Affairs Diabetes Trial (VADT)

OBJECTIVE

To determine risk factors in clinically significant macular edema (CSME) and if increased CSME in minorities is due to ethnicity or other factors in the Veterans Affairs Diabetes Trial (VADT).

METHODS

CSME prevalence based on 7-field stereo fundus photographs in 1268 patients with type 2 diabetes was related to ethnicity, demographics and biochemistries by univariate and multivariate analyses.

RESULTS

Hispanics (H) made up 17.5% and African Americans (AA) 17.7% of the cohort. CSME prevalence was 10%. In univariate analysis, CSME was more prevalent in H, 18%, and AA, 15.6% than in non-Hispanic Whites (NHW), 6.3%, p<0.01. Univariate regression of CSME associated with younger age, younger onset of diabetes; longer duration; retinopathy severity; and high HbA1c, BP, urine albumin/creatinine, and amputation, all p<0.01. In multivariate regression, CSME was associated with ethnicity/race (Hispanic White vs. non-Hispanic White, OR, (95% CI), 2.30, (1.35-3.92), p<0.01; African American vs. non-Hispanic White, 2.30, (1.33-4.00), p<0.01), diastolic BP (1.13 per 5 mm Hg, (1.02-1.23), p=0.03), amputation (3.0, (1.11-8.13), p=0.04), and retinopathy severity ( approximately 30, ( approximately 17 to approximately 59), p<0.01).

CONCLUSION

The prevalence of CSME in the VADT is associated with ethnicity as well as diastolic BP, amputation, and retinopathy severity.

Glycemic control in youth with diabetes: the SEARCH for diabetes in Youth Study

OBJECTIVE

To assess correlates of glycemic control in a diverse population of children and youth with diabetes.

STUDY DESIGN

This was a cross-sectional analysis of data from a 6-center US study of diabetes in youth, including 3947 individuals with type 1 diabetes (T1D) and 552 with type 2 diabetes (T2D), using hemoglobin A(1c) (HbA(1c)) levels to assess glycemic control.

RESULTS

HbA(1c) levels reflecting poor glycemic control (HbA(1c) >or= 9.5%) were found in 17% of youth with T1D and in 27% of those with T2D. African-American, American Indian, Hispanic, and Asian/Pacific Islander youth with T1D were significantly more likely to have higher HbA(1c) levels compared with non-Hispanic white youth (with respective rates for poor glycemic control of 36%, 52%, 27%, and 26% vs 12%). Similarly poor control in these 4 racial/ethnic groups was found in youth with T2D. Longer duration of diabetes was significantly associated with poorer glycemic control in youth with T1D and T2D.

CONCLUSIONS

The high percentage of US youth with HbA(1c) levels above the target value and with poor glycemic control indicates an urgent need for effective treatment strategies to improve metabolic status in youth with diabetes.

Association of A1C and fasting plasma glucose levels with diabetic retinopathy prevalence in the U.S. population: Implications for diabetes diagnostic thresholds

OBJECTIVE

To examine the association of A1C levels and fasting plasma glucose (FPG) with diabetic retinopathy in the U.S. population and to compare the ability of the two glycemic measures to discriminate between people with and without retinopathy.

RESEARCH DESIGN AND METHODS

This study included 1,066 individuals aged >or=40 years from the 2005-2006 National Health and Nutrition Examination Survey. A1C, FPG, and 45 degrees color digital retinal images were assessed. Retinopathy was defined as a level >or=14 on the Early Treatment Diabetic Retinopathy Study severity scale. We used joinpoint regression to identify linear inflections of prevalence of retinopathy in the association between A1C and FPG.

RESULTS

The overall prevalence of retinopathy was 11%, which is appreciably lower than the prevalence in people with diagnosed diabetes (36%). There was a sharp increase in retinopathy prevalence in those with A1C >or=5.5% or FPG >or=5.8 mmol/l. After excluding 144 people using hypoglycemic medication, the change points for the greatest increase in retinopathy prevalence were A1C 5.5% and FPG 7.0 mmol/l. The coefficients of variation were 15.6 for A1C and 28.8 for FPG. Based on the areas under the receiver operating characteristic curves, A1C was a stronger discriminator of retinopathy (0.71 [95% CI 0.66-0.76]) than FPG (0.65 [0.60 - 0.70], P for difference = 0.009).

CONCLUSIONS

The steepest increase in retinopathy prevalence occurs among individuals with A1C >or=5.5% and FPG >or=5.8 mmol/l. A1C discriminates prevalence of retinopathy better than FPG.

Glycaemia-independent ethnic differences in HbA(1c) in subjects with impaired glucose tolerance

AIM

To study the ethnic differences in HbA(1c) between Whites and South Asians with impaired glucose tolerance.

METHODS

We audited 75g oral glucose tolerance tests (OGTT) performed in Clinical Chemistry, New Cross Hospital, Wolverhampton over 1 year. HbA(1c) and glycaemia were compared between Whites and South Asians with impaired glucose intolerance (IGT).

RESULTS

There were 46 South Asians (22 female) and 88 Whites (41 female). South Asian subjects were younger (59.2 +/- 14.31 vs. 67.6 +/- 12.63 yrs; P < 0.001) and weighed less (78.1 +/- 17.2 vs. 87.47 +/- 19.1 kgs; P < 0.001) than White subjects. HbA(1c) levels were higher (6.5 +/- 0.7 vs. 6.1 +/- 0.6%; P < 0.001) in South Asians compared to Whites. Fasting glucose (5.71 +/- 0.5 vs. 5.93 +/- 0.7; P = 0.039) was lower in South Asians but 2hour glucose (10.5 +/- 1.0 vs. 10.40 +/- 0.9; P = 0.404) was similar in both ethnic groups.

CONCLUSION

South Asians have higher HbA(1c) levels than Whites despite lower fasting glucose value on OGTT, indicating ethnic differences in HbA(1c) are due to glycaemia-independent factors.

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.

Circulating biomarkers of glycemia in diabetes management and implications for personalized medicine

Personalized medicine represents a new model in how the medical community approaches disease management. Rather than managing those with a particular diagnosis according to an established guideline, the personalized medicine model seeks to identify unique characteristics within each patient that can serve as a basis for disease characterization and specialized treatment. This article reviews several circulating biomarkers of glycemia that are used in the medical management of diabetes, to include hemoglobin A1c, fructosamine, and 1,5-anhydroglucitol. Within the discussion, specific attention is paid to areas in which biomarker results do not correlate with anticipated results based on actual mean glycemia. Variability between actual and anticipated results of the various biomarker tests represents opportunities to identify previously undefined subcategories of diabetes and groups of patients that fit into these subcategories. Finally, research areas are proposed for these subcategories that would further promote the field of personalized medicine in diabetes.

Do race and ethnicity impact hemoglobin A1c independent of glycemia?

Hemoglobin A1c (HbA1c) is widely used as an index of mean glycemia, a measure of risk for the development of diabetes complications, and a measure of the quality of diabetes care. Emerging literature suggests that, although HbA1c levels change little over time within persons without diabetes, they vary considerably among individuals, suggesting that factors other than glycemia may impact HbA1c. Racial and ethnic differences in HbA1c have been described that do not appear to be explained by differences in glycemia. It is imperative that the nonglycemic factors that affect HbA1c be more clearly defined. Even more important, it must be determined whether differences among individuals or groups correlate with susceptibility to complications or merely reflect variation in hemoglobin glycation.

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.

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.

Racial and ethnic differences in mean plasma glucose, hemoglobin A1c, and 1,5-anhydroglucitol in over 2000 patients with type 2 diabetes

CONTENT

Recent studies have reported hemoglobin A(1c) (A1c) differences across racial/ethnic groups. Our diverse population allows for further investigation of potential differences in measurements of glycemia.

OBJECTIVES

Our objectives were to describe and explore baseline racial/ethnic differences in self-monitored plasma glucose profiles, A1c, and 1,5-anhydroglucitol (1,5-AG) in patients with type 2 diabetes enrolled in the Assessing DURAbility of Basal vs. Lispro Mix 75/25 Insulin Efficacy trial.

DESIGN, SETTING, PATIENTS

The trial enrolled 2094 patients with type 2 diabetes, ages 30-80 yr, from 11 countries.

MAIN OUTCOME MEASURES

Estimated mean plasma glucose (MPG), A1c, and 1,5-AG were compared among racial/ethnic groups before and after adjusting for factors affecting glycemia: age, sex, duration of diabetes, body mass index, and MPG.

RESULTS

Baseline estimated MPG +/- sd was 220.0 +/- 82.0 mg/dl, mean A1c was 9.0 +/- 1.3%, and 1,5-AG was 5.0 +/- 4.1microg/ml. Estimated MPG did not differ between Caucasian and non-Caucasian groups. A1c was higher in Hispanics (9.4 +/- 1.4%; P < 0.001), Asians (9.2 +/- 1.4%; P < 0.01), and patients of other racial/ethnic groups (9.7 +/- 1.5%; P < 0.001) compared with Caucasians (8.9 +/- 1.2%). Paradoxically, 1,5-AG was higher for Asian (5.7 +/- 4.6 microg/ml) and African patients (6.2 +/- 5.4 microg/ml) vs. Caucasians (4.9 +/- 3.9 microg/ml) (P < 0.01). After adjusting for factors affecting glycemia, A1c was higher (all P <or= 0.002) in Hispanics, Asians, Africans, and patients of other racial/ethnic groups, and 1,5-AG was higher in Asian and African patients (P < 0.001) vs. Caucasians.

CONCLUSIONS

There were differences in A1c and 1,5-AG, but not MPG, among racial/ethnic groups. Comparisons of glycemia across racial/ethnic groups using these parameters may be problematic due to inherent biological variability and methodological issues.

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.

Review of hemoglobin A(1c) in the management of diabetes

Hemoglobin HbA(1c) (A(1c)) has been used clinically since the 1980s as a test of glycemic control in individuals with diabetes. The Diabetes Control and Complications Trial (DCCT) demonstrated that tight glycemic control, quantified by lower blood glucose and A(1c) levels, reduced the risk of the development of complications from diabetes. Subsequently, standardization of A(1c) measurement was introduced in different countries to ensure accuracy in A(1c) results. Recently, the International Federation of Clinical Chemists (IFCC) introduced a more precise measurement of A(1c) , which has gained international acceptance. However, if the IFCC A(1c) result is expressed as a percentage, it is lower than the current DCCT-aligned A(1c) result, which may lead to confusion and deterioration in diabetic control. Alternative methods of reporting have been proposed, including A(1c) -derived average glucose (ADAG), which derives an average glucose from the A(1c) result. Herein, we review A(1c) , the components involved in A(1c) formation, and the interindividual and assay variations that can lead to differences in A(1c) results, despite comparable glycemic control. We discuss the proposed introduction of ADAG as a surrogate for A(1c) reporting, review imprecisions that may result, and suggest alternative clinical approaches.

Ethnic variation in the correlation between random serum glucose concentration and glycated haemoglobin

AIMS

To determine if the relationship between serum glucose concentration and glycated haemoglobin is different between African-Americans and whites.

METHODS

Retrospective cross-sectional study comparing the association between glycated haemoglobin and serum glucose levels, based upon ethnicity. Two databases were evaluated: (i) 4215 African-American and 6359 white outpatients who had simultaneous glycated haemoglobin, random serum glucose and creatinine concentration measurements between 2000 and 2007 at the North Carolina Baptist Hospital and (ii) 1021 white and 312 African-American Diabetes Heart Study (DHS) participants.

RESULTS

In North Carolina Baptist Hospital clinic attendees, a given glycated haemoglobin was associated with higher serum glucose concentrations in African-Americans compared with whites. In a multivariate model with glycated haemoglobin as the outcome variable, racial differences remained significant after adjustment for serum glucose, age, gender and kidney function. For individuals with a serum glucose between 5.6 and 8.3 mmol/l, the glucose : glycated haemoglobin ratio was 1.03 +/- 0.16 mmol/l/% in white individuals and 0.99 +/- 0.17 mmol/l/% in African-Americans (P < 0.0001). For a glycated haemoglobin value of 7.0%, there was a 0.98-mmol/l difference in predicted serum glucose concentration in 50-year-old African-American men, relative to white. Results were replicated in the DHS, where in a best-fit linear model, after adjustment for glucose, African-American race was a significant predictor of glycated haemoglobin (P < 0.0001).

CONCLUSIONS

African-Americans have higher glycated haemoglobin values at given serum glucose concentrations relative to whites. This finding may contribute to the observed difference in glycated haemoglobin values reported between these race groups.

Hemoglobin A1c: past, present and future

Hemoglobin A1c (HbA1c) has been used for decades to monitor the control of glycemia in diabetes. Although HbA1cis currently undergoing a reassessment, and major developments have been underway in recent years, HbA1c is not recommended at present for diabetes screening or diagnosis. The objective of this review is to summarize the recent developments and to review a potential diagnostic role for HbA1c. Implementation of changes in HbA1c results and units of measurements have been suggested for the purpose of test standardization. These include lower reference ranges (by about 1.5-2 points) and measurement units expressed in percentage (%), as mg/dL (mmol/L) or mmol/mol (or a combination of these units). In diabetes screening and diagnosis, the current diagnostic guidelines use measurement of plasma glucose either fasting or after glucose load. These diagnostic methods have shortcomings warranting a potential diagnostic role for HbA1c. While recent developments in HbA1c methodologies are acknowledged, it is not yet known which changes will be implemented, and how soon. Given the recent literature supporting HbA1c diagnostic abilities, and given the shortcomings of the current guidelines, it is possible that a diagnostic role for HbA1c may be considered in future practice guidelines, globally. Very recently, the first of such recommendations has been proposed by an expert panel, as announced by the US Endocrine Society.

Approach to the patient with prediabetes

Prediabetes consists of impaired fasting glucose and/or impaired glucose tolerance and is a significant risk factor for the development of type 2 diabetes, microvascular, and macrovascular disease. The values used to define prediabetes are arbitrary, because prediabetes represents an intermediary category along the continuum from normal glucose levels and tolerance to overt hyperglycemia. The progression from prediabetes to type 2 diabetes occurs over many years, strong evidence to support intervention to delay the progression from prediabetes to diabetes. Large, randomized prospective studies with lifestyle intervention and/or various modes of pharmacotherapy have demonstrated successful delay of diabetes. Several issues in the management of prediabetes remain controversial, such as the role of pharmacotherapy and when to escalate treatment. This article will review some of the issues surrounding the identification and treatment of prediabetes, with an interpretation of the available data to help guide management.

Mitigating case mix factors by choice of glycemic control performance measure threshold

OBJECTIVE

Performance measures are tools for assessing quality of care but may be influenced by patient factors. We investigated how currently endorsed performance measures for glycemic control in diabetes may be influenced by case mix composition. We assessed differences in A1C performance measure threshold attainment by case mix factors for A1C >9% and examined how lowering the threshold to A1C >8% or >7% changed these differences.

RESEARCH DESIGN AND METHODS

Using data from the 1999-2002 National Health and Nutrition Examination Survey for 843 adults self-reporting diabetes, we computed the mean difference in A1C threshold attainment of >9, >8, and >7% by various case mix factors. The mean difference is the average percentage point difference in threshold attainment for population groups compared with that for the overall population.

RESULTS

Diabetes medication was the only factor for which the difference in threshold attainment increased at lower thresholds, with mean differences of 5.7 percentage points at A1C >9% (reference), 10.1 percentage points at A1C >8% (P < 0.05), and 14.1 percentage points at A1C >7% (P < 0.001).

CONCLUSIONS

As 87% of U.S. adults have A1C <9%, a performance measure threshold of >9% will not drive major improvements in glycemic control. Lower thresholds do not exacerbate differences in threshold attainment for most factors. Reporting by diabetes medication use may compensate for heterogeneous case mix when a performance measure threshold of A1C >8% or lower is used.

The proposed terminology 'A(1c)-derived average glucose' is inherently imprecise and should not be adopted

The proposed use of a more precise standard for glycated (A(1c)) and non-glycated haemoglobin would lead to an A(1c) value, when expressed as a percentage, that is lower than that currently in use. One approach advocated to address the potential confusion that would ensue is to replace 'HbA(1c)' with a new term, 'A(1c)-derived average glucose.' We review evidence from several sources suggesting that A(1c) is, in fact, inherently imprecise as a measure of average glucose, so that the proposed terminology should not be adopted.

Frequency of HbA1c discordance in estimating blood glucose control

PURPOSE OF REVIEW

HbA1c is a trusted standard for monitoring glycemic control and predicting complications. However, there are emerging issues complicating the interpretation of HbA1c that the clinician caring for patients with diabetes needs to consider.

RECENT FINDINGS

There is increasing evidence of the potential for mismatches between HbA1c and other measures of glycemia which require some caution in HbA1c interpretation. We have attempted to characterize the nature of these discordances by developing the concept of the 'glycation gap' in which differences in protein glycation occurring in the intracellular space (HbA1c) versus in the extracellular space (measured as fructosamine) are compared. We have evidence that HbA1c results discordant from other measures of glycemic control may be secondary to previously unappreciated physiological variables, including erythrocyte lifespan, in hematologically normal individuals. We relate these findings to a number of HbA1c interpretation issues important for diabetes care: factors affecting hemoglobin glycation, relationship of HbA1c to glycemia, standardization of the HbA1c assay, and HbA1c relation to complications.

SUMMARY

There are an increasing number of clinical circumstances in which there are nuances to HbA1c interpretation such that standard norms for assessment of glycemic control or complication risk may need to be modified.

A new look at screening and diagnosing diabetes mellitus

OBJECTIVE

Diabetes is underdiagnosed. About one third of people with diabetes do not know they have it, and the average lag between onset and diagnosis is 7 yr. This report reconsiders the criteria for diagnosing diabetes and recommends screening criteria to make case finding easier for clinicians and patients.

PARTICIPANTS

R.M.B. invited experts in the area of diagnosis, monitoring, and management of diabetes to form a panel to review the literature and develop consensus regarding the screening and diagnosis of diabetes with particular reference to the use of hemoglobin A1c (HbA1c). Participants met in open session and by E-mail thereafter. Metrika, Inc. sponsored the meeting.

EVIDENCE

A literature search was performed using standard search engines.

CONSENSUS PROCESS

The panel heard each member's discussion of the issues, reviewing evidence prior to drafting conclusions. Principal conclusions were agreed on, and then specific cut points were discussed in an iterative consensus process.

CONCLUSIONS

The main factors in support of using HbA1c as a screening and diagnostic test include: 1) HbA1c does not require patients to be fasting; 2) HbA1c reflects longer-term glycemia than does plasma glucose; 3) HbA1c laboratory methods are now well standardized and reliable; and 4) errors caused by nonglycemic factors affecting HbA1c such as hemoglobinopathies are infrequent and can be minimized by confirming the diagnosis of diabetes with a plasma glucose (PG)-specific test. Specific recommendations include: 1) screening standards should be established that prompt further testing and closer follow-up, including fasting PG of 100 mg/dl or greater, random PG of 130 mg/dl or greater, or HbA1c greater than 6.0%; 2) HbA1c of 6.5-6.9% or greater, confirmed by a PG-specific test (fasting plasma glucose or oral glucose tolerance test), should establish the diagnosis of diabetes; and 3) HbA1c of 7% or greater, confirmed by another HbA1c- or a PG-specific test (fasting plasma glucose or oral glucose tolerance test) should establish the diagnosis of diabetes. The recommendations are offered for consideration of the clinical community and interested associations and societies.

Proteomic profiling of nonenzymatically glycated proteins in human plasma and erythrocyte membranes

Nonenzymatic glycation of peptides and proteins by d-glucose has important implications in the pathogenesis of diabetes mellitus, particularly in the development of diabetic complications. In this work, we report the first proteomics-based characterization of nonenzymatically glycated proteins in human plasma and erythrocyte membranes from individuals with normal glucose tolerance, impaired glucose tolerance, and type 2 diabetes mellitus. Phenylboronate affinity chromatography was used to enrich glycated proteins and glycated tryptic peptides from both human plasma and erythrocyte membranes. The enriched peptides were subsequently analyzed by liquid chromatography coupled with electron transfer dissociation-tandem mass spectrometry, resulting in the confident identification of 76 and 31 proteins from human plasma and erythrocyte membranes, respectively. Although most of the glycated proteins could be identified in samples from individuals with normal glucose tolerance, slightly higher numbers of glycated proteins and more glycation sites were identified in samples from individuals with impaired glucose tolerance and type 2 diabetes mellitus.

Disparities in A1C levels between Hispanic and non-Hispanic white adults with diabetes: a meta-analysis

OBJECTIVE

Hispanics have higher rates of diabetes and diabetes-related complications than do non-Hispanic whites. A meta-analysis was conducted to estimate the difference between the mean values of A1C for these two groups.

RESEARCH DESIGN AND METHODS

We executed a PubMed search of articles published from 1993 through July 2007. Data sources included PubMed, Web of Science, Cumulative Index to Nursing and Allied Health, the Cochrane Library, Combined Health Information Database, and Education Resources Information Center. Data on sample size, age, sex, A1C, geographical location, and study design were extracted. Cross-sectional data and baseline data from clinical trials and cohort studies for Hispanics and non-Hispanic whites with diabetes were included. Studies were excluded if they included individuals <18 years of age or patients with pre-diabetes or gestational diabetes.

RESULTS

A total of 495 studies were reviewed, of which 73 contained data on A1C for Hispanics and non-Hispanic whites, and 11 met the inclusion criteria. Meta-analysis revealed a statistically significant mean difference (P < 0.0001) of -0.46 (95% CI -0.63 to -0.33), correlating to an approximately 0.5% higher A1C for Hispanics. Grouping studies by design (cross-sectional or cohort), method of data collection for A1C (chart review or blood sampling), and care type (managed or nonmanaged) yielded similar results.

CONCLUSIONS

In this meta-analysis, A1C was approximately 0.5% higher in Hispanic patients with diabetes than in non-Hispanic patients. Understanding the reasons for this disparity should be a focus for future research.