High glycosylated hemoglobin levels increase the risk of progression to diabetes mellitus in subjects with glucose intolerance

Development of type 2 diabetes mellitus in people with intermediate hyperglycaemia

BACKGROUND

Intermediate hyperglycaemia (IH) is characterised by one or more measurements of elevated blood glucose concentrations, such as impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and elevated glycosylated haemoglobin A1c (HbA1c). These levels are higher than normal but below the diagnostic threshold for type 2 diabetes mellitus (T2DM). The reduced threshold of 5.6 mmol/L (100 mg/dL) fasting plasma glucose (FPG) for defining IFG, introduced by the American Diabetes Association (ADA) in 2003, substantially increased the prevalence of IFG. Likewise, the lowering of the HbA1c threshold from 6.0% to 5.7% by the ADA in 2010 could potentially have significant medical, public health and socioeconomic impacts.

OBJECTIVES

To assess the overall prognosis of people with IH for developing T2DM, regression from IH to normoglycaemia and the difference in T2DM incidence in people with IH versus people with normoglycaemia.

SEARCH METHODS

We searched MEDLINE, Embase, ClincialTrials.gov and the International Clinical Trials Registry Platform (ICTRP) Search Portal up to December 2016 and updated the MEDLINE search in February 2018. We used several complementary search methods in addition to a Boolean search based on analytical text mining.

SELECTION CRITERIA

We included prospective cohort studies investigating the development of T2DM in people with IH. We used standard definitions of IH as described by the ADA or World Health Organization (WHO). We excluded intervention trials and studies on cohorts with additional comorbidities at baseline, studies with missing data on the transition from IH to T2DM, and studies where T2DM incidence was evaluated by documents or self-report only.

DATA COLLECTION AND ANALYSIS

One review author extracted study characteristics, and a second author checked the extracted data. We used a tailored version of the Quality In Prognosis Studies (QUIPS) tool for assessing risk of bias. We pooled incidence and incidence rate ratios (IRR) using a random-effects model to account for between-study heterogeneity. To meta-analyse incidence data, we used a method for pooling proportions. For hazard ratios (HR) and odds ratios (OR) of IH versus normoglycaemia, reported with 95% confidence intervals (CI), we obtained standard errors from these CIs and performed random-effects meta-analyses using the generic inverse-variance method. We used multivariable HRs and the model with the greatest number of covariates. We evaluated the certainty of the evidence with an adapted version of the GRADE framework.

MAIN RESULTS

We included 103 prospective cohort studies. The studies mainly defined IH by IFG5.6 (FPG mmol/L 5.6 to 6.9 mmol/L or 100 mg/dL to 125 mg/dL), IFG6.1 (FPG 6.1 mmol/L to 6.9 mmol/L or 110 mg/dL to 125 mg/dL), IGT (plasma glucose 7.8 mmol/L to 11.1 mmol/L or 140 mg/dL to 199 mg/dL two hours after a 75 g glucose load on the oral glucose tolerance test, combined IFG and IGT (IFG/IGT), and elevated HbA1c (HbA1c5.7: HbA1c 5.7% to 6.4% or 39 mmol/mol to 46 mmol/mol; HbA1c6.0: HbA1c 6.0% to 6.4% or 42 mmol/mol to 46 mmol/mol). The follow-up period ranged from 1 to 24 years. Ninety-three studies evaluated the overall prognosis of people with IH measured by cumulative T2DM incidence, and 52 studies evaluated glycaemic status as a prognostic factor for T2DM by comparing a cohort with IH to a cohort with normoglycaemia. Participants were of Australian, European or North American origin in 41 studies; Latin American in 7; Asian or Middle Eastern in 50; and Islanders or American Indians in 5. Six studies included children and/or adolescents.Cumulative incidence of T2DM associated with IFG5.6, IFG6.1, IGT and the combination of IFG/IGT increased with length of follow-up. Cumulative incidence was highest with IFG/IGT, followed by IGT, IFG6.1 and IFG5.6. Limited data showed a higher T2DM incidence associated with HbA1c6.0 compared to HbA1c5.7. We rated the evidence for overall prognosis as of moderate certainty because of imprecision (wide CIs in most studies). In the 47 studies reporting restitution of normoglycaemia, regression ranged from 33% to 59% within one to five years follow-up, and from 17% to 42% for 6 to 11 years of follow-up (moderate-certainty evidence).Studies evaluating the prognostic effect of IH versus normoglycaemia reported different effect measures (HRs, IRRs and ORs). Overall, the effect measures all indicated an elevated risk of T2DM at 1 to 24 years of follow-up. Taking into account the long-term follow-up of cohort studies, estimation of HRs for time-dependent events like T2DM incidence appeared most reliable. The pooled HR and the number of studies and participants for different IH definitions as compared to normoglycaemia were: IFG5.6: HR 4.32 (95% CI 2.61 to 7.12), 8 studies, 9017 participants; IFG6.1: HR 5.47 (95% CI 3.50 to 8.54), 9 studies, 2818 participants; IGT: HR 3.61 (95% CI 2.31 to 5.64), 5 studies, 4010 participants; IFG and IGT: HR 6.90 (95% CI 4.15 to 11.45), 5 studies, 1038 participants; HbA1c5.7: HR 5.55 (95% CI 2.77 to 11.12), 4 studies, 5223 participants; HbA1c6.0: HR 10.10 (95% CI 3.59 to 28.43), 6 studies, 4532 participants. In subgroup analyses, there was no clear pattern of differences between geographic regions. We downgraded the evidence for the prognostic effect of IH versus normoglycaemia to low-certainty evidence due to study limitations because many studies did not adequately adjust for confounders. Imprecision and inconsistency required further downgrading due to wide 95% CIs and wide 95% prediction intervals (sometimes ranging from negative to positive prognostic factor to outcome associations), respectively.This evidence is up to date as of 26 February 2018.

AUTHORS' CONCLUSIONS

Overall prognosis of people with IH worsened over time. T2DM cumulative incidence generally increased over the course of follow-up but varied with IH definition. Regression from IH to normoglycaemia decreased over time but was observed even after 11 years of follow-up. The risk of developing T2DM when comparing IH with normoglycaemia at baseline varied by IH definition. Taking into consideration the uncertainty of the available evidence, as well as the fluctuating stages of normoglycaemia, IH and T2DM, which may transition from one stage to another in both directions even after years of follow-up, practitioners should be careful about the potential implications of any active intervention for people 'diagnosed' with IH.

Implications of risk stratification for diabetes prevention: the case of hemoglobin A1c

Although glycated hemoglobin (HbA1c) has been widely recommended for the diagnosis of diabetes, considerable ambiguity remains about how HbA1c should be used to identify people with prediabetes or other high-risk states for preventive interventions. The current paper provides a synthesis of the epidemiologic basis and the health and economic implications of using various HbA1c-based risk-stratification approaches for diabetes prevention. HbA1c predicts diabetes and related outcomes across a wide range of HbA1c values. However, the authors estimate that, among U.S. adults, the top 15% of the nondiabetic HBA1c distribution (HbA1c of 5.7%-6.4%) accounts for 47% of diabetes cases over 5 years, and the top 30% (5.5%-6.4%) accounts for about 70% of cases. Although this clustering of eventual cases at the high end of the HbA1c risk distribution means that intervention resources will be more efficient when applied to the upper end of the distribution, no obvious threshold exists to prioritize people for preventive interventions. Thus, the choice of optimal thresholds is a tradeoff, wherein selecting a lower HbA1c cut-point will lead to a higher rate of eligibility and health benefits for more people, and a higher HbA1c cut-point will lead to fewer cases of diabetes prevented but greater "economic efficiency" in terms of diabetes cases prevented per intervention participant. Selection of optimal HbA1c thresholds also may change with the evolving science, as better evidence on the biologic effectiveness of lower-intensity interventions and effects of lifestyle interventions on additional outcomes could pave the way for a more comprehensive, tiered approach to risk stratification.

Glycated haemoglobin and the risk of cardiovascular disease, diabetes and all-cause mortality in the Copenhagen City Heart Study

OBJECTIVE

Individuals with diabetes mellitus (DM) have a considerably elevated risk of developing serious health problems including cardiovascular disease (CVD). Long-term elevated levels of blood glucose in nondiabetic individuals may also be associated with increased risk of CVD. The aim of this study was to investigate the relationships between glycated haemoglobin A(1c) (HbA(1c) ) and CVD, DM and all-cause mortality.

SUBJECTS AND DESIGN

The Copenhagen City Heart Study is a prospective study of individuals from the Danish general population. The cohort was followed for 10 years via national registers with respect to incident CVD, DM and all-cause mortality. Follow-up was 100% complete.

RESULTS

A total of 5127 subjects were included, of whom 597 had DM. In the nondiabetic population, HbA(1c) was significantly associated with incident CVD events in both univariate [hazard ratio (HR) 1.38, 95% CI 1.11-1.71] and multivariate analyses (HR 1.31, 95% CI 1.05-1.64). In the nondiabetic population, increased levels of HbA(1c) were correlated with developing DM. There was a threefold increase in risk of incident DM per unit increase in HbA(1c) with a univariate HR of 3.83 (95% CI 1.96-7.51). This relationship was essentially unchanged after multivariate adjustments (HR 4.19, 95% CI 2.01-8.71). Furthermore, we found that net reclassification improvement for diagnosed DM and CVD was significantly improved with the addition of HbA(1c) in the analyses. Although not statistically significant, we found a strong trend towards an association between HbA(1c) and all-cause mortality (HR 1.21, 95% CI 0.99-1.47). We did not find the same associations amongst the population with DM.

CONCLUSION

In the Danish general population, HbA(1c) was strongly associated with CVD in individuals without DM.

Cut-off values of fasting and post-load plasma glucose and HbA1c for predicting Type 2 diabetes in community-dwelling Japanese subjects: the Hisayama Study

AIMS

We examined the optimal cut-off values of fasting plasma glucose, 2-h post-load glucose and HbA(1c) for predicting Type 2 diabetes in community-dwelling Japanese subjects.

METHODS

A total of 1982 subjects without diabetes aged 40-79 years who underwent a 75-g oral glucose tolerance test were followed prospectively for 14 years by annual health examination.

RESULTS

During the follow-up, 295 subjects developed Type 2 diabetes. Compared with the first decile, the crude hazard ratio for incident Type 2 diabetes was significantly higher in the fifth fasting plasma glucose decile [5.4-5.4 mmol/l (97-98 mg/dl)] or higher, in the seventh 2-h post-load glucose decile [6.9-7.2 mmol/l (124-131 mg/dl)] or higher, and in the fifth HbA(1c) decile [34-36 mmol/mol (5.3-5.4%)] or higher. These associations remained substantially unchanged even after adjustment for confounding factors. The receiver operating characteristic curve analysis showed that the optimal cut-off values for predicting Type 2 diabetes were 5.6 mmol/l (101 mg/dl) for fasting plasma glucose, 6.9 mmol/l (124 mg/dl) for 2-h post-load glucose and 37 mmol/mol (5.5%) for HbA(1c). In a stratified analysis, the cut-off values were approximately 5.6 mmol/l (101 mg/dl) for fasting plasma glucose and 37 mmol/mol (5.5%) for HbA(1c), and these values were unchanged over BMI quartile levels, whereas the 2-h post-load glucose cut-off values declined with decreasing BMI levels.

CONCLUSIONS

Our findings suggest that the cut-off value for predicting Type 2 diabetes in the Japanese population is 5.6 mmol/l (101 mg/dl) for fasting plasma glucose and 37 mmol/mol (5.5%) for HbA(1c), while the 2-h post-load glucose cut-off value is lower than the diagnostic criterion for impaired glucose tolerance.

Patterns of glycemic control using glycosylated hemoglobin in diabetics

Aim:

Till now estimation of blood glucose is the highly effective method for diagnosing diabetes mellitus but it provides a short-term picture of control. More evidence is required to prove that plasma glucose and glycosylated hemoglobin levels together gives a better estimate of glycemic control and compliance with treatment. Indian diabetes risk score (IDRS) is a simplified screening tool for identifying undiagnosed diabetic subjects, requires minimum time, and effort and can help to considerably reduce the costs of screening.

Objective:

To study patterns of glycemic control using glycosylated hemoglobin in diabetic patients. To find out correlation between levels of plasma glucose and glycosylated hemoglobin in diabetics and to calculate IDRS of the study population.

Materials and Methods:

A cross sectional study was conducted among 300 known diabetic patients attending outpatient department of a rural medical college in Haryana, India. Following standard procedures and protocols FPG and glycosylated hemoglobin were measured to find out a pattern of glycemic control in them after taking their written and informed consent. A correlation between the levels of glycosylated hemoglobin and fasting blood glucose was also calculated. These patients were made to fill a performa and their demographic and clinical risk factors were noted and based on this, their IDRS was calculated. This was done to validate the IDRS in Indian rural population.

Results:

Fifty-two percent of the population had fasting plasma glucose level between 125-150 mg/dl, 21% had this level between 151-175 mg/dl. Thirteen percent of the study subjects had HbA1C between 6.5-7.5, more than half (57.3%) had this value between 7.5-8.5, 12% and 18% had values between 8.5-9.5 and 9.5-10.5, respectively. Twelve percent of the participants had HbA1C level higher than 10.5. Correlation of fasting plasma glucose level and HbA1C was also studied and found that correlation coefficient came out to be .311. This correlation was found to be statistically significant (P = .007). Sixty-five percent of the case had IDRS higher than 60.

Conclusions:

Glycaemic control in diabetics can be better assessed with glycosylated hemoglobin and FPG together. A positive correlation between FPG and HbA1c allows for the use of HbA1c along with FPG in diagnosing type 2 DM but the two should not be used interchangeably. IDRS can be used as a screening tool for diabetes.

Estimation of the contribution of biomarkers of different metabolic pathways to risk of type 2 diabetes

The contribution of different biological pathways to the development of type 2 diabetes was quantified in a case-cohort design based on circulating blood biomarkers from participants aged 35-65 years in the EPIC-Potsdam Study. The analytic sample included 613 participants with incident diabetes and 1965 participants without diabetes. The proportion that each biomarker contributed to the risk of diabetes was quantified using effect decomposition method. Summarized risk of each biomarker was estimated by an index based on quintiles of gamma-glutamyltransferase (GGT), HDL-cholesterol, hs-CRP, and adiponectin. Cox proportional hazard regression was used to estimate relative risks adjusted for age, sex, body mass index, waist-circumference, education, sport activity, cycling, occupational activity, smoking, alcohol intake, and consumptions of red meat, coffee and whole grain bread. Adiponectin explained a total of 32.1% (CI = 16.8, 49.1%) of the risk related to index. For the other biomarkers the corresponding proportions were 23.5% (CI = 10.1, 37.8%) by HDL-cholesterol, 21.5% (CI = 11.5, 32.8%) by GGT, and 15.5% (CI = 4.44, 27.3%) by hs-CRP. The results support the hypothesis that the different biological pathways reflected by GGT, HDL-cholesterol, hs-CRP and adiponectin independent from each other contribute to the risk of type 2 diabetes. Of these pathways the highest contribution was observed for adiponectin which contributed one-third to the risk and that equal proportion was contributed by GGT and HDL-cholesterol, although the contribution of inflammation was lower.

A1C level and future risk of diabetes: a systematic review

We examined ranges of A1C useful for identifying persons at high risk for diabetes prior to preventive intervention by conducting a systematic review. From 16 included studies, we found that annualized diabetes incidence ranged from 0.1% at A1C <5.0% to 54.1% at A1C >or=6.1%. Findings from 7 studies that examined incident diabetes across a broad range of A1C categories showed 1) risk of incident diabetes increased steeply with A1C across the range of 5.0 to 6.5%; 2) the A1C range of 6.0 to 6.5% was associated with a highly increased risk of incident diabetes, 25 to 50% incidence over 5 years; 3) the A1C range of 5.5 to 6.0% was associated with a moderately increased relative risk, 9 to 25% incidence over 5 years; and 4) the A1C range of 5.0 to 5.5% was associated with an increased incidence relative to those with A1C <5%, but the absolute incidence of diabetes was less than 9% over 5 years. Our systematic review demonstrated that A1C values between 5.5 and 6.5% were associated with a substantially increased risk for developing diabetes.

The use of dried blood spot sampling in the national social life, health, and aging project

OBJECTIVES

This paper describes the methods used for and issues associated with collection and analysis of dried blood spot (DBS) samples for the National Social Life, Health, and Aging Project and provides the basic distributions of the resulting analytes.

METHODS

DBSs from capillary finger sticks were collected by nonmedically trained interviewers from 2,044 individuals, aged 57-85 years. The quality and quantity of DBS samples were evaluated to allow for analysis of interviewer performance. Levels of C-reactive protein, antibodies to the Epstein-Barr virus, hemoglobin, and glycosylated hemoglobin were assayed using various analytic methods.

RESULTS

Cooperation rate for DBS collection was 84.5%, with 99% of the cards yielding enough sample for at least one analysis. The distribution, mean, and standard deviation of the analytes obtained from DBSs are also presented in this paper.

CONCLUSIONS

The high cooperation rate and quality of the spots collected suggest that the collection of DBSs in population-based research is a feasible and viable alternative to venous blood draws. The relative ease of sample collection, transport, and storage are significant benefits. Care should be taken, however, when comparing results from analysis of DBS samples with those obtained from serum or plasma samples.

Haemoglobin A1c analysis in the management of patients with diabetes: from chaos to harmony: Table 1

Effective management of patients with diabetes mellitus requires accurate assessments of blood glucose control. The best characterised marker of long term glycaemic control is whole blood haemoglobin A1c (HbA1c). Published clinical trials have identified quantitative and direct relationships between the HbA1c concentration and risks of diabetic microvascular complications. However, in order to practice evidence-based medicine, assays used to measure patient samples should ideally produce values comparable to the assays used in these trials. Numerous assays using chromatographic and immunological detection methods are used around the world. This paper briefly reviews the scientific evolution of HbA1c and its analysis, discusses the reasons why HbA1c assay standardisation is a challenge, describes the approaches that have been adopted to harmonise HbA1c assays, and addresses the current initiatives to standardise HbA1c globally. These efforts have established HbA1c as an essential component in the management of patients with diabetes mellitus and are likely to lead to the use of HbA1c in the screening/diagnosis of diabetes.

Hemoglobin A1c predicts diabetes but not cardiovascular disease in nondiabetic women

BACKGROUND

Hemoglobin A1c (HbA1c) is a marker of cumulative glycemic exposure over the preceding 2- to 3-month period. Whether mild elevations of this biomarker provide prognostic information for development of clinically evident type 2 diabetes and cardiovascular disease among individuals at usual risk for these disorders is uncertain.

METHODS

We examined baseline HbA1c levels as a predictor of incident clinical diabetes and cardiovascular disease (nonfatal myocardial infarction, coronary revascularization procedure, ischemic stroke, or death from cardiovascular causes) in a prospective cohort study beginning in 1992 of 26,563 US female health professionals aged 45 years or more without diagnosed diabetes or vascular disease (median follow-up 10.1 years).

RESULTS

During follow-up, 1238 cases of diabetes and 684 cardiovascular events occurred. In age-adjusted analyses using quintiles of HbA1c, a risk gradient was observed for both incident diabetes and cardiovascular disease. After multivariable adjustment, HbA1c remained a strong predictor of diabetes but was no longer significantly associated with incident cardiovascular disease. In analyses of threshold effects, adjusted relative risks for incident diabetes in HbA1c categories of less than 5.0%, 5.0% to 5.4%, 5.5% to 5.9%, 6.0% to 6.4%, 6.5% to 6.9%, and 7.0% or more were 1.0, 2.9, 12.1, 29.3, 28.2, and 81.2, respectively. Risk associations persisted after additional adjustment for C-reactive protein and after excluding individuals developing diabetes within 2 and 5 years of follow-up.

CONCLUSIONS

These prospective findings suggest that HbA1c levels are elevated well in advance of the clinical development of type 2 diabetes, supporting recent recommendations for lowering of diagnostic thresholds for glucose metabolic disorders. In contrast, the association of HbA1c with incident cardiovascular events is modest and largely attributable to coexistent traditional risk factors.

Prevention of type 2 diabetes

Type 2 diabetes is a major cause of morbidity and mortality resulting from its microangiopathic and macroangiopathic complications. Current approaches to its management and to the prevention of diabetic complications are difficult to implement effectively, and there is little evidence to date that these approaches are reducing the impact of this disease. The recognition that type 2 diabetes usually has a prolonged prediabetic phase raises the possibility that the emergence of hyperglycemia and the atherosclerotic complications associated with diabetes may be preventable by the institution of early treatment modalities. Sufficient data suggest that life-style modification or pharmacotherapy directed at improving insulin sensitivity or insulin secretion in subjects with impaired glucose tolerance may reduce progression to diabetes. Two long-term prospective, controlled trials have been initiated to test this hypothesis.