Ethnic disparity in hemoglobin A1c levels among normoglycemic offspring of parents with type 2 diabetes mellitus

Evidence-based screening, clinical care and health education recommendations for Alaska Native peoples with prediabetes living in southcentral Alaska: findings from the Alaska EARTH follow-up study

Pre-diabetes (pre-DM) is a strong predictor of diabetes (DM) over time. This study investigated how much of the recent increase in pre-DM identified among Alaska Native (AN) peoples living in urban southcentral Alaska may be due to changes in diagnostic methods. We used clinical and demographic data collected at baseline between 2004 and 2006 and at follow-up collected between 2015 and 2017 from the urban southcentral Alaska Education and Research Towards Health (EARTH) cohort. We used descriptive statistics and logistic regression to explore differences in demographic and clinical variables among the identified pre-DM groups. Of 388 participants in the follow-up study, 243 had A1c levels indicating pre-DM with only 20 demonstrating pre-DM also by fasting blood glucose (FBG). Current smoking was the sole predictor for pre-DM by A1c alone while abdominal obesity and elevated FBG-predicted pre-DM by A1c+FBG. No participants had an elevated FBG without an A1c elevation. A substantial portion of the rise in pre-DM found among urban southcentral AN peoples in the EARTH follow-up study was due to the addition of A1c testing. Pre-DM by A1c alone should be used to motivate behavioural changes that address modifiable risk factors, including smoking cessation, physical activity and weight management.

Racial differences in measures of glycemia in the Vitamin D and Type 2 Diabetes (D2d) Study: a secondary analysis of a randomized trial

INTRODUCTION

Understanding how race may influence the association between A1c and glycemia can improve diabetes screening. We sought to determine whether, for a given A1c level, glucose levels during an oral glucose tolerance test (OGTT) differed by race.

RESEARCH DESIGN AND METHODS

From data collected at 22 US clinical sites, we conducted a cross-sectional study of concurrently measured A1c and OGTT and observational longitudinal follow-up of the subset with high-risk pre-diabetes. Numerical integration methods were used to calculate area under the glycemic curve (AUCglu) during OGTT and least squares regression model to estimate A1c for a given AUCglu by race, controlling for potential confounders.

RESULTS

1016 black, 2658 white, and 193 Asian persons at risk of diabetes were included in cross-sectional analysis. Of these, 2154 with high-risk pre-diabetes were followed for 2.5 years. For a given A1c level, AUCglu was lower in black versus white participants. After adjustment for potential confounders, A1c levels for a given AUCglu quintile were 0.15-0.20 and 0.02-0.19 percentage points higher in black and Asian compared with white participants, respectively (p<0.05). In longitudinal analyses, black participants were more likely to be diagnosed with diabetes by A1c than white participants (28% vs 10%, respectively; p<0.01). Black and Asian participants were less likely to be diagnosed by fasting glucose than white participants (16% vs 15% vs 37%, respectively; p<0.05). Black participants with A1c levels in the lower-level quintiles had greater increase in A1c over time compared with white participants.

CONCLUSIONS

Use of additional testing beyond A1c to screen for diabetes may better stratify diabetes risk in the diverse US population.

Investigating family history of diabetes as a predictor of fasting insulin and fasting glucose activity in a sample of healthy weight adults

AIMS

Type 2 diabetes is a major public health problem for the global community. Having a family history of diabetes significantly increases risk for diabetes development and understanding how family history contributes to diabetes risk could lead to more effective prevention efforts for at-risk individuals. In a previous study, we showed family history of diabetes is a significant predictor of fasting insulin in healthy weight children. The present study aimed to use the National Health and Nutrition Examination Survey (NHANES 2017) to apply similar multiple regression models to a population of healthy weight adults to determine if family history is a significant predictor of fasting glucose and fasting insulin.

METHODS

Fasting glucose (mg/dL) and fasting insulin (pmol/L) were used as dependent variables in each model, respectively, with family history of diabetes as the independent variable. Covariates for each model included age, gender, race/ethnicity, waist circumference, and macronutrient intake.

RESULTS

The model significantly predicted the variance of fasting glucose [(F(11,364) = 34.80, p < 0.001, R² = 0.2342] and fasting insulin [F(11,343) = 17.58, p < 0.001, R² = 0.1162]. After adjusting for covariates, family history was a significant predicator of fasting glucose (p = 0.0193) as well as age, gender, non-Hispanic black ethnicity, waist circumference, and fat intake. Significant predictors of fasting insulin included gender and waist circumference, but not family history (p = 0.8264). In addition, fasting glucose was higher in individuals with a family history of diabetes (p = 0.033).

CONCLUSIONS

These results add to the understanding of how family history influences the biomarkers that contribute to diabetes development. Knowledge of how family history of diabetes relates to fasting insulin and fasting glucose activity in healthy weight individuals can be used to design personalized screening and early prevention strategies.

Glucose-independent racial disparity in HbA1c is evident at onset of type 1 diabetes

OBJECTIVE

Higher levels of HbA1c, independent of blood glucose levels, have been described in Blacks compared to Whites patients with established diabetes. The goal of this study was to determine if glucose-independent racial disparity in HbA1C is evident at diabetes onset.

RESEARCH DESIGN AND METHODS

We conducted a retrospective single-center chart review of 189 youth with new onset Type 1 diabetes (T1D) 60 % Whites and 40 % Blacks. HbA1c, glucose and other biochemistry measures were obtained at presentation in the Emergency Department before initiation of any therapy. HbA1c levels were adjusted for presenting glucose, self-identified race, age, gender, hematocrit, and RDW-CV.

RESULTS

Blacks with T1D had statistically significant higher unadjusted HbA1c (11.9 ± 1.9 vs 11.04 ± 2.0 %, p = 0.004), initial glucose (530.6 ± 230.4 vs 442 ± 211.3 mg/dL, p = 0.0075) and lower pHs (7.28 ± 0.15 vs 7.33 ± 0.12, p = 0.02) compared to white patients. Least squares means of HbA1c remained higher in Black patients even after statistical adjustment for presenting glucose, age, gender, RDW-CV, and pH. In a multiple variable model (R² = 0.38, p < 0.0001) c-peptide was influenced by HCO₃ (p = 0.0035), gender (p = 0.0092), BMI (p < 0.0001), but not race or glucose.

CONCLUSIONS

HbA1c at initial presentation of T1D is higher in young Black patients compared to Whites even after adjustment for glucose, age, gender, and RDW-CV. This racial disparity is consistent with other studies in individuals without diabetes and patients with long-standing diabetes under treatment.

Excess serum uric acid is associated with metabolic syndrome in obese adolescent patients

Purpose

Obesity is a significant cause of morbidity in adolescents. Excess serum uric acid (SUA) has been associated with metabolic syndrome (MS) among adults. We evaluated the relationship among SUA and markers of insulin resistance (IR) and low-grade inflammation in obese adolescents with and without MS.

Methods

The study was a retrospective chart review of obese patients seen in the LeBonheur Endocrine clinic seen in clinic between September 2016 and December 2017. MS was defined as according to the International Diabetes Federation. Body mass index standard deviation score (BMI SDS), systolic blood pressure (SBP), diastolic blood pressure (DBP), body composition, fasting lipids, glucose, high sensitivity c-reactive protein (hs-CRP), serum uric acid (SUA), HbA1c, alanine transferase (ALT), aspartate transferase (AST), insulin and homeostatic model assessment for insulin resistance (HOMA-IR) were extracted from the charts of the 100 obese adolescents (57% female).

Results

Hyperuricemia (SUA >357 umol/L) was present in 41.8% of entire cohort without significant ethnic/racial and/or gender differences. Adolescents with HUA had higher FM, SBP, HbA1c, insulin and HOMA-IR (p < 0.05). While SUA was positively correlated with FM, SBP, HOMA-IR and HbA1c, and triglyceride:HDL-C ratio (TG:HDL-C) (p < 0.05). MS was identified in 32.8% of cohort. MS showed significantly higher FM, SBP, DBP, SUA, ALT, insulin, HOMA-IR, and TG:HDL-c ratio than non-MS subgroup (p < 0.05). FM was positively correlated with SUA, HOMA-IR and hsCRP (p < 0.01).

Conclusions

In our study, those with hyperuricemia (HUA) showed elevated markers of metabolic syndrome including BP, serum glucoses, IR and triglycerides. In our cohort, SUA appears to correlate with MS comorbidities.

A labile form of hemoglobin A1c is higher in African-American youth with type 1 diabetes compared to Caucasian patients at similar glucose levels

BACKGROUND

Hemoglobin A1c (HbA1c) levels are higher in African-American (AA) individuals compared to Caucasians (EA) even after adjustment for blood glucose levels. To better understand the mechanism of this disparity we examined the relationship of an unstable (labile) form of HbA1c (L-HbA1c) with race and glucose.

METHODS

Samples for HbA1c were collected from pediatric patients self-identified as either AA (15F, 12M, age 13.4 ± 3.5 years) or EA (22F, 30M, age 14.6 ± 3.4 years) with type 1 diabetes at the time of a clinic visit. Clinic HbA1c (HbA1c) was performed by immunoassay. L-HbA1c equaled the difference in the HbA1c fraction by dynamic capillary isoelectric focusing before and after incubation in a low pH buffer. A capillary glucose (Clinic-BG) was measured at clinic visit. Mean blood glucose (MBG) was calculated from the last 30 days of the patient's glucose meter data. The influence of race on L-HbA1c was assessed in a multiple variable regression model adjusted for Clinic-BG.

RESULTS

The groups were similar for age and duration of diabetes. L-HbA1c was correlated with Clinic-BG, MBG, and HbA1c. The mean levels of L-HbA1c, HbA1c, MBG, but not Clinic-BG were higher in AA patients compared to EA. After adjustment for Clinic-BG, L-HbA1c was still higher in AA (2.8 ± 0.7% AA vs 2.1 ± 0.7% EA, P < .0001).

CONCLUSIONS

L-HbA1c is correlated with Clinic-BG. At any given level of Clinic-BG, AA patients have higher levels of L-HbA1c than EA. This preliminary study suggests that early factors prior to the formation of stable HbA1c may contribute to the observed glucose-independent racial disparity.

Genetic Ancestry Markers and Difference in A1c Between African American and White in the Diabetes Prevention Program

PURPOSE

HbA1c levels are higher in blacks than non-Hispanic whites (NHWs). We investigated whether genetics could explain this difference in Diabetes Prevention Program (DPP) participants.

METHODS

We tested (i) genetic variants causing hemoglobinopathies, (ii) a genetic risk score (GRS) based on 60 variants associated with HbA1c from genome-wide association meta-analysis, and (iii) principal component (PC) factors that capture continental ancestry derived from genetic markers distributed across the genome.

RESULTS

Of 2658 eligible DPP participants, 537 (20%) self-identified as black and 1476 (56%) as NHW. Despite comparable fasting and 2-hour glucose levels, blacks had higher HbA1c (mean ± SD = 6.2 ± 0.6%) compared with NHWs (5.8 ± 0.4%; P < 0.001). In blacks, the genetic variant causing sickle cell trait was associated with higher HbA1c [β (SE) = +0.44 (0.08)%; P = 2.1 × 10-4]. The GRS was associated with HbA1c in both blacks and NHWs. Self-identified blacks were distributed along the first PC axis, as expected in mixed ancestry populations. The first PC explained 60% of the 0.4% difference in HbA1c between blacks and NHWs, whereas the sickle cell variant explained 16% and GRS explained 14%.

CONCLUSIONS

A large proportion of HbA1c difference between blacks and NHWs was associated with the first PC factor, suggesting that unidentified genetic markers influence HbA1c in blacks in addition to nongenetic factors.

Issues in Defining the Burden of Prediabetes Globally

PURPOSE OF REVIEW

Using a global perspective, this review collates evidence on the heterogeneity of prediabetes definitions and diagnostic methods, their clinical and public health implications, and discusses possible options for improvement.

RECENT FINDINGS

Our review notes that the concept of prediabetes is increasingly recognized worldwide, but against a background of non-uniform definition and diagnostic criteria. This results in widely varying burden estimation. Current evidence shows a variety of prediabetes phenotypes. This reflects biological and diagnostic heterogeneity, resulting from the use of different tests (glucose or HbA_1C) and thresholds to define prediabetes. The biological and diagnostic variabilities have implications for the characterization of the burden of prediabetes, natural history, prognosis, screening, implementation of lifestyle or drug interventions to mitigate related health risks, and monitoring of the effects of such interventions.

Impact of Genetic Determinants of HbA1c on Type 2 Diabetes Risk and Diagnosis

PURPOSE OF REVIEW

Glycated hemoglobin (A1c) is used to diagnose type 2 diabetes and monitor glycemic control. Specific genetic variants interfere with A1c and effects/frequencies of some variants vary by ancestry. In this review, we summarize findings from large trans-ethnic meta-analyses of genome-wide association studies (GWAS) of A1c and describe some variants influencing erythrocyte biology and interfering with A1c.

RECENT FINDINGS

Recent GWAS meta-analyses have revealed 60 loci associated with A1c in multi-ethnic populations. The main A1c genetic driver in African Americans is rs1050828 (G6PD). Some identified loci are located in/near genes known as monogenic causes of erythrocytic disorders (ANK1, SPTA1) or iron disorders (TMPRSS6, HFE). Uncommon genetic variants (not revealed by GWAS) that are known to cause hemoglobinopathies may also influence A1C levels, partly by interfering with laboratory assays. Specific genetic variants that have a large impact on A1c levels may influence clinical practice, especially in individuals of African descent. Efforts to reveal novel A1c loci should focus on increasing representation of GWAS in non-European ancestries, and on using better genome-wide coverage of uncommon variants that are specific to each population.

Prediabetes and Cardiovascular Disease: Pathophysiology and Interventions for Prevention and Risk Reduction

Prediabetes is a state characterized by impaired fasting glucose or impaired glucose tolerance. This review discusses the pathophysiology and macrovascular complications of prediabetes. The pathophysiologic defects underlying prediabetes include insulin resistance, alpha- and beta-cell dysfunction, increased lipolysis, inflammation, and suboptimal incretin effect. Recent studies have revealed that the long-term complications of diabetes manifest in some people with prediabetes; these complications include microvascular and macrovascular disorders. Finally, we present an overview of randomized control trials aimed at preventing progression from prediabetes to type 2 diabetes and discuss their implications for macrovascular risk reduction.

Assessment of disturbed glucose metabolism and surrogate measures of insulin sensitivity in obese children and adolescents

BACKGROUND

With the rising prevalence of obesity and type 2 diabetes (T2D) in obese children, it is becoming imperative to detect disturbed glucose metabolism as early as possible in order to prevent T2D development.

SUBJECTS/METHODS

Cross-sectional study of 92 obese children (median age 11.7 years, 51% female) and 7 lean children (median age 11.4 years, 57% female) who underwent an oral glucose tolerance test (OGTT) in a tertiary pediatric care center. Glucose tolerance was assessed and different indices for β-cell function, insulin sensitivity and insulin secretion were calculated.

RESULTS

Nineteen obese children were identified with prediabetes (PD, 12 impaired glucose tolerance, 4 increased fasting glucose and 3 combined). Compared with the 73 obese children with normal glucose tolerance (nGT), subjects with PD had higher insulin resistance, but lower insulin sensitivity and β-cell function, although their glycated hemoglobin (HbA1c) levels were comparable. The Whole Body Insulin Sensitivity Index (WBISI) and β-cell function by Insulin Secretion-Sensitivity Index-2 (ISSI-2) strongly correlated with the OGTT glucose area under the curve 0-120 min (r = 0.392, p < 0.0002; r = 0.547, p < 0.0001, respectively). When testing the relation between early insulin response during OGTT by insulinogenic index and insulin sensitivity assessed by WBISI, a hyperbolic relationship between insulin secretion and insulin sensitivity was found. The calculated disposition index was lower in subjects with PD vs. nGT (median 459 vs. 792, p = 0.004). We identified the OGTT 30-min/120-min insulin ratio as a simple marker, which is significantly lower in obese children with vs. without PD (median 0.87 vs. 1.29, p = 0.021) and which has a better sensitivity and specificity for detecting PD than HbA1c among obese children.

CONCLUSIONS

Children with identified PD had changes of several markers for β-cell function, insulin sensitivity and resistance before changes in HbA1c occurred. The lower disposition index indicates that these children have already inadequate β-cell compensation for the degree of insulin resistance.

Influence of West African Ethnicity and Gender on Beta-Cell Function and Insulin Sensitivity in Essential Hypertensives Treated with Hydrochlorothiazide and Hydrochlorothiazide-lisinopril Combination

OBJECTIVE

To assess the effects of hydrochlorothiazide (HCT) given alone and in combination with an angiotensin-converting enzyme inhibitor (ACEI) on beta-cell function in a negroid population to further explore possible ethnic differences in the effect of antihypertensive drugs on homeostasis model assessment - insulin resistance (HOMA-IR).

MATERIALS AND METHODS

A total of 80 newly diagnosed Nigerian essential hypertensive patients were assigned to receive either HCT 25 mg daily or both HCT and lisinopril (Lis; 25/10 mg daily) in an open-label study for 12 weeks. The treatment groups were well matched in clinical and demographic baseline features. Changes in HOMA-IR from baseline to end of study (week 12), fasting plasma glucose (FPG), serum potassium, serum insulin, and blood pressure over the same period were also evaluated.

RESULTS

After 12 weeks, mean delta HOMA-IR (and %) was higher in the HCT monotherapy group; although, this change did not reach statistical significance in both groups -0.1 ± 7.1, P = 0.538 (HCT) and 0.6 ± 4.2 P = 0.913 (HCT + Lis); an insignificant increase was observed in FPG and serum insulin in both groups, whereas serum potassium decreased in similar fashion. Blood pressure reduction was similar in both groups. Analysis of HOMA-IR change according to gender in response to HCT mono- or combination therapy with Lis showed no significant difference.

CONCLUSIONS

HCT monotherapy in hypertensive indigenous Nigerians, was not associated with worse metabolic effects when compared with combination therapy using Lis, an ACEI after 12 weeks. Low-dose thiazide diuretic as first-line antihypertensive medication may be safe in the short-term, further larger and long-term studies are needed to corroborate this finding.

Effect of ethnicity on HbA1c levels in individuals without diabetes: Systematic review and meta-analysis

Aims/Hypothesis

Disparities in HbA1c levels have been observed among ethnic groups. Most studies were performed in patients with diabetes mellitus (DM), which may interfere with results due to the high variability of glucose levels. We conducted a systematic review and meta-analysis to investigate the effect of ethnicity on HbA1c levels in individuals without DM.

Methods

This is a systematic review with meta-analysis. We searched MEDLINE and EMBASE up to September 2016. Studies published after 1996, performed in adults without DM, reporting HbA1c results measured by certified/standardized methods were included. A random effects model was used and the effect size was presented as weighted HbA1c mean difference (95% CI) between different ethnicities as compared to White ethnicity.

Results

Twelve studies met the inclusion criteria, totalling data from 49,238 individuals. There were significant differences between HbA1c levels in Blacks [0.26% (2.8 mmol/mol); 95% CI 0.18 to 0.33 (2.0 to 3.6), p <0.001; I² = 90%, p <0.001], Asians [0.24% (2.6 mmol/mol); 95% CI 0.16 to 0.33 (1.7 to 3.6), p <0.001; I² = 80%, p = 0.0006] and Latinos [0.08% (0.9 mmol/mol); IC 95% 0.06 to 0.10 (0.7 to 1.1); p <0.001; I² = 0%; p = 0.72] when compared to Whites.

Conclusions/Interpretation

This meta-analysis shows that, in individuals without DM, HbA1c values are higher in Blacks, Asians, and Latinos when compared to White persons. Although small, these differences might have impact on the use of a sole HbA1c point to diagnose DM in all ethnic populations.

Do glycemic marker levels vary by race? Differing results from a cross-sectional analysis of individuals with and without diagnosed diabetes

OBJECTIVE

It is well known that A1c varies by race. However, racial differences in other biomarkers of hyperglycemia are less well characterized. The objective of this study was to determine whether average levels of glycemic markers differ by race in adults with and without diagnosed diabetes, before and after accounting for postchallenge glucose.

RESEARCH DESIGN AND METHODS

This cross-sectional study included 2692 middle-aged men and women (5.5% with diagnosed diabetes; 44% African-American; and 56% white) from the Coronary Artery Risk Development in Young Adults Study (2005-2006) who had fasting glucose, 2-hour postchallenge glucose, A1c, glycated albumin, fructosamine, and 1,5-anhydroglucitol (1,5-AG) measured. Multiple linear regression was used to evaluate racial differences in mean levels of each glycemic marker stratified by the diabetes status and adjusted for sociodemographics, cardiovascular factors, and postchallenge glucose.

RESULTS

Among those with diagnosed diabetes, racial differences were not observed for any of the glycemic markers. In contrast, among those without diagnosed diabetes, African-Americans had higher mean levels than whites of A1c (β=0.19% points; 95% CI 0.14 to 0.24), glycated albumin (β=0.82% points; 95% CI 0.68 to 0.97), fructosamine (β=8.68 μmol/L; 95% CI 6.68 to 10.68), and 2-hour glucose (β=3.50 mg/dL; 95% CI 0.10 to 6.90) after multivariable adjustment, whereas there were no statistically significant racial difference in 1,5-AG. The racial differences observed for A1c, glycated albumin, and fructosamine persisted after further adjustment for fasting and 2-hour glucose and were of similar magnitude (SD units).

CONCLUSIONS

Racial differences in glycemic marker levels were evident among middle-aged adults without diagnosed diabetes even after adjustment for postchallenge glucose. Whether these racial differences in biomarkers of hyperglycemia affect the risk of complications warrants additional study.

Genetic Associations of PPARGC1A with Type 2 Diabetes: Differences among Populations with African Origins

The aim of this study was to assess the differences in correlation of PPARGC1A polymorphisms with type 2 diabetes (T2D) risk in adults of African origins: African Americans and Haitian Americans. The case-control study consisted of >30 years old, self-identified Haitian Americans (n = 110 cases and n = 116 controls) and African Americans (n = 124 cases and n = 122 controls) living in South Florida with and without T2D. Adjusted logistic regression indicated that both SNP rs7656250 (OR = 0.22, P = 0.005) and rs4235308 (OR = 0.42, P = 0.026) showed protective association with T2D in Haitian Americans. In African Americans, however, rs4235308 showed significant risk association with T2D (OR = 2.53, P = 0.028). After stratification with sex, in Haitian Americans, both rs4235308 (OR = 0.38, P = 0.026) and rs7656250 (OR = 0.23, P = 0.006) showed protective association with T2D in females whereas in African American males rs7656250 had statistically significant protective effect on T2D (OR = 0.37, P = 0.043). The trends observed for genetic association of PPARGC1A SNPs, rs4235308, and rs7656250 for T2D between Haitian Americans and African Americans point out differences in Black race and warrant replicative study with larger sample size.

Diabetes Complications at Presentation and One Year by Glycated Haemoglobin at Diagnosis in a Multiethnic and Diverse Socioeconomic Population: Results from the South London Diabetes Study

Background. WHO's recommendation of HbA1c ≥ 48 mmol/mol (6.5%) as diagnostic for type 2 diabetes mellitus (T2DM) was adopted by three UK London boroughs in May 2012. The South London Diabetes (SOUL-D) study has recruited people with newly diagnosed T2DM since 2008. We compared participants diagnosed before May 2012 with HbA1c < 48 mmol/mol to those with diagnostic HbA1c ≥ 48 mmol/mol. Methods. A prospective cohort study of newly diagnosed T2DM participants from 96 primary care practices, comparing demographic and biomedical variables between those with diagnostic HbA1c < 48 mmol/mol or HbA1c ≥ 48 mmol/mol at recruitment and after one year. Results. Of 1488 participants, 22.8% had diagnostic HbA1c < 48 mmol/mol. They were older and more likely to be white (p < 0.05). At recruitment and one year, there were no between-group differences in the prevalence of diabetic complications, except that those diagnosed with HbA1c < 48 mmol/mol had more sensory neuropathy at recruitment (p = 0.039) and, at one year, had new myocardial infarction (p = 0.012) but less microalbuminuria (p = 0.012). Conclusions. Use of HbA1c ≥ 48 mmol/mol as the sole T2DM diagnostic criterion may miss almost a quarter of those previously diagnosed in South London yet HbA1c < 48 mmol/mol may not exclude clinically important diabetes.

Glucoregulatory function among African Americans and European Americans with normal or pre-diabetic hemoglobin A1c levels

OBJECTIVE

A hemoglobin (Hb) A1c range of 5.7%-6.4% has been recommended for the diagnosis of prediabetes. To determine the significance of such "prediabetic" HbA1c levels, we compared glucoregulatory function in persons with HbA1c levels of 5.7%-6.4% and those with HbA1c<5.7%.

METHODS

We studied 280 nondiabetic adults (142 black, 138 white; mean (±SD) age 44.2±10.6 years). Each subject underwent clinical assessment, blood sampling for HbA1c measurement, and a 75-g oral glucose tolerance test at baseline. Additional assessments during subsequent outpatient visits included insulin sensitivity, using homeostasis model assessment (HOMA)-IR and the hyperinsulinemic euglycemic clamp; insulin secretion, using HOMA-B and frequently samples intravenous glucose tolerance test (FSIVGTT) and disposition index (DI); and measurement of fat mass, using DXA.

RESULTS

Compared to subjects with HbA1c<5.7%, persons with HbA1c levels of 5.7%-6.4% were older, and had higher body mass index (BMI) and insulin secretion but similar insulin sensitivity. When the two groups were matched in age and BMI, persons with HbA1c 5.7%-6.4% were indistinguishable from those with HbA1c <5.7% with regard to all measures of glycemia and glucoregulatory function.

CONCLUSIONS

Unlike glucose-defined prediabetes status, an HbA1c range of 5.7%-6.4% does not reliably identify individuals with impaired insulin action or secretion, the classical defects underlying the pathophysiology of prediabetes. Thus, HbA1c cannot validly replace blood glucose measurement in the diagnosis of prediabetes. If utilized as a screening test due to convenience, aberrant HbA1c values should be corroborated with blood glucose measurement before therapeutic intervention.

Lack of racial disparity in incident prediabetes and glycemic progression among black and white offspring of parents with type 2 diabetes: the pathobiology of prediabetes in a biracial cohort (POP-ABC) study

BACKGROUND

Although the incidence of type 2 diabetes (T2D) among persons with prediabetes is well known (∼10%/y), the incidence of prediabetes among normoglycemic persons is unclear. Also, in the Diabetes Prevention Program, no racial/ethnic differences were seen in diabetes incidence, whereas marked racial/ethnic disparities are reported in the prevalence of T2D. We aimed to obtain estimates of incident prediabetes and determine whether racial disparities manifest during transition to prediabetes.

DESIGN AND METHODS

We enrolled 376 (217 black, 159 white) nondiabetic offspring of parents with T2D (mean age 44.2 y) and followed them up quarterly for 5.5 years. Assessments included anthropometry, body composition, oral glucose tolerance test, biochemistries, energy expenditure, insulin sensitivity, and insulin secretion. The primary outcome was progression to impaired fasting glucose and/or impaired glucose tolerance (or diabetes).

RESULTS

Of 343 participants with evaluable data, 101 subjects (49 white, 52 black) developed prediabetes, and 10 (4 white, 6 black) developed diabetes during a mean follow-up of 2.62 years. There was no significant racial difference in the cumulative incidence of prediabetes (32.7% white, 30% black) or combined prediabetes/diabetes (35% white, 30% black). Significant predictors of prediabetes included age, gender, trunk fat, 2-hour postload glucose (2hrPG), insulin sensitivity, and insulin secretion. In a Cox proportional-hazards model, with adjustment for age and sex, the 2hrPG and abdominal obesity were independent predictors of incident prediabetes/diabetes [relative hazards (95% confidence interval [CI]) for the 90th vs 10th percentile: trunk fat mass 2.90 (95% CI 1.74-4.82), P < .0001; 2hrPG 2.54 (95% CI 1.46-4.40), P = .0009]. Having the trunk fat mass and the 2hrPG at the 90th percentile conferred a 7-fold hazard of prediabetes compared with persons at the 10th percentile for both measures.

CONCLUSION

Black and white offspring of parents with type 2 diabetes develop prediabetes at a similar high rate of approximately 11% per year. Therefore, close surveillance, with prompt intervention to prevent dysglycemia, is warranted in persons with parental diabetes.

Glucose-independent ethnic differences in HbA1c in people without known diabetes

OBJECTIVE

To determine whether glucose-independent differences in HbA1c exist between people of African, South Asian, and Chinese ethnicities.

RESEARCH DESIGN AND METHODS

Data from 6,701 people aged 19-78 years, without known diabetes, from Mauritius, and participating in the population-based Non-Communicable Disease Surveys of the main island and the island of Rodrigues were included. Participants were African (n = 1,219 from main island, n = 1,505 from Rodrigues), South Asian (n = 3,820), and Chinese (n = 157). Survey data included HbA1c, plasma glucose during oral glucose tolerance testing (OGTT), anthropometry, demographics, and medical and lifestyle history.

RESULTS

Mean HbA1c, after adjustment for fasting and 2-h plasma glucose and other factors known to influence HbA1c, was higher in Africans from Rodrigues (6.1%) than in South Asians (5.7%, P < 0.001), Chinese (5.7%, P < 0.001), or Africans from the main island of Mauritius (5.7%, P < 0.001). The age-standardized prevalence of diabetes among Africans from Rodrigues differed substantially depending on the diagnostic criteria used [OGTT 7.9% (95% CI 5.8-10.0); HbA1c 17.3% (15.3-19.2)]. Changing diagnostic criteria resulted in no significant change in the prevalence of diabetes within the other ethnic groups.

CONCLUSIONS

People of African ethnicity from Rodrigues have higher HbA1c than those of South Asian or African ethnicity from the main island of Mauritius for reasons not explained by plasma glucose during an OGTT or traditional factors known to affect glycemia. Further research should be directed at determining the mechanism behind this disparity and its relevance to clinical outcomes.

Pathobiology of Prediabetes in a Biracial Cohort (POP-ABC) study: baseline characteristics of enrolled subjects

BACKGROUND

The Pathobiology of Prediabetes in a Biracial Cohort (POP-ABC) study is a prospective evaluation of the natural history impaired glucose regulation.

DESIGN AND METHODS

The eligibility requirements include age 18-65 yr, history of type 2 diabetes in one or both parents, normal fasting plasma glucose (FPG) or normal glucose tolerance, and African-American or Caucasian status. Participants underwent assessments (including dietary and exercise behavior, clinical examination, glucose tolerance, insulin sensitivity, β-cell function, body composition, energy expenditure) during 2.25-5.5 yr of quarterly follow-up. The primary outcome is the occurrence of prediabetes. Baseline data are presented for the 376 enrolled participants. The cohort was also compared with National Health and Nutrition Examination Survey 2007/2008 participants meeting the age and glycemic criteria for the POP-ABC study.

RESULTS

The POP-ABC cohort [mean (±SD) age was 44.2 ± 10.6 yr] was 57.7% African-Americans, 42.3% Caucasians, and 70.7% females; 86% had one parent with diabetes and 14% had both parents affected. Although greater than 70% of the cohort were employed and 75% had more than 13 yr of education, more African-Americans reported incomes less than $20,000 and fewer reported incomes more than $75,000 compared with Caucasians. Compared with Caucasians, African-Americans had a higher body mass index (31.3 ± 7.8 vs. 28.8 ± 7.8 kg/m(2), P = 0.001), a lower FPG (90.0 ± 7.72 vs. 92.2 ± 7.60 mg/dl, P = 0.008), higher glycosylated hemoglobin, lower triglycerides, and similar blood pressure, and homeostasis model assessment of insulin resistance, homeostasis model assessment of β-cell function, high-density lipoprotein, and low-density lipoprotein cholesterol levels. Compared with a cross-section of U.S. subjects (National Health and Nutrition Examination Survey 2007/2008) with normal FPG and normal glucose tolerance, participants in the POP-ABC study had similar lipid profile but were more educated and had higher body mass index, glycosylated hemoglobin, and blood pressure.

CONCLUSIONS

The POP-ABC study has successfully enrolled healthy African-American and Caucasian adults with parental type 2 diabetes mellitus. The study will generate novel data on incidence rates and predictors of prediabetes, and clarify the role of race/ethnicity on early dysglycemia.