HbA1c in relation to incident diabetes and diabetes-related complications in non-diabetic adults at baseline
Patricia Anne Metcalf1, Cam Kyle2, Tim Kenealy3
1Department of Epidemiology & Biostatistics, School of Population Health, University of Auckland; Department of Statistics, University of Auckland.
Insights
Glycated hemoglobin (HbA1c) is a convenient alternative to oral glucose tolerance tests (oGTT) for predicting diabetes and related complications. HbA1c showed stronger associations with mortality and cardiovascular events than fasting glucose.
Area of Science:
- Endocrinology
- Cardiovascular Medicine
- Diabetes Research
Background:
- Glycemic control is crucial for managing diabetes and preventing complications.
- Both glycated hemoglobin (HbA1c) and oral glucose tolerance tests (oGTT) are used to assess glucose metabolism.
- Non-diabetic individuals require accurate risk stratification for incident diabetes and related adverse outcomes.
Purpose of the Study:
- To compare the predictive utility of HbA1c and 2-hour 75g oral glucose tolerance test (oGTT) in non-diabetic adults.
- To evaluate associations with incident diabetes, all-cause mortality, cardiovascular disease (CVD) mortality, CVD events, coronary heart disease (CHD), ischemic stroke, and microvascular complications.
- To determine the most effective glycemic measure for risk prediction in a general population.
Main Methods:
- Prospective linkage of community data with hospitalization, mortality, pharmaceutical, and laboratory records in New Zealand.
- Inclusion of 31,148 adults with available HbA1c and 2-h 75g oGTT, excluding those with prior diabetes diagnosis or treatment.
- Multivariable Cox proportional hazards regression analysis to compare glycemic measures and outcomes, adjusting for confounders.
Main Results:
- After adjustment, 2-hour glucose levels showed the highest hazard ratios for incident diabetes and microvascular complications (retinopathy, nephropathy), followed by HbA1c and then fasting glucose.
- HbA1c concentrations were significantly associated with all-cause mortality and CHD.
- Ischemic stroke and CVD events were uniquely associated with 2-hour glucose, while circulatory complications showed a stronger association with HbA1c.
Conclusions:
- HbA1c demonstrates stronger associations with mortality and cardiovascular outcomes compared to fasting glucose.
- HbA1c serves as a practical and convenient alternative to the oGTT for risk assessment in non-diabetic individuals.
- While 2-hour glucose is superior for predicting incident diabetes and microvascular complications, HbA1c offers broader predictive value for mortality and major cardiovascular events.
Aims:
We compared the utility of glycated hemoglobin (HbA1c) and oral glucose tolerance (oGTT) in non-diabetic patients for identifying incident diabetes; all-cause mortality; cardiovascular disease (CVD) mortality; CVD, coronary heart disease (CHD), and ischemic stroke events; and diabetes microvascular complications.
Methods:
Data from a New Zealand community setting were prospectively linked to hospitalization, mortality, pharmaceutical and laboratory test results data. After applying exclusion criteria (prior laboratory diagnosis or history of drug treatment for diabetes or hospitalization for diabetes or CVD event), there were 31,148 adults who had an HbA1c and 2-h 75g oGTT. HbA1c was measured by ion-exchange high-performance liquid chromatography, and glucose using a commercial enzymatic method. We compared glycemic measures and outcomes using multivariable Cox proportional hazards regression.
Results:
The median follow-up time was 4years (range 0 to 13). The mean age was 57·6years and 53·0% were male. After adjusting for other glycemic measures (fasting glucose, 2-h glucose and/or HbA1c where relevant) in addition to age, sex, ethnicity and smoking habit, the hazard ratios for incident diabetes and diabetes complications of retinopathy and nephropathy were highest for 2-h glucose levels, followed by HbA1c and lastly by fasting glucose. However, all-cause mortality and CHD were significantly associated with HbA1c concentrations only, and ischemic stroke and CVD events with 2-h glucose only. Circulatory complications showed a stronger association with HbA1c.
Conclusion:
Apart from neuropathy, HbA1c showed stronger associations with outcomes compared to fasting glucose and provides a convenient alternative to an oGTT.
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