• This longitudinal study looked at data from the Health, Aging, and Body Composition study. “Older adults with both elevated IFG and HbA1c have 26.2 times the risk of developing diabetes over 7 years compared with those with normal values.

• IFG and HbA1c could be a very helpful tool for clinicians screening patients at risk for diabetes.”

– Tony Nimeh, MD

This study looked at fasting glucose, HbA1c, and the combination of the two tests to predict the development of diabetes. Patients with elevations in both had a 26-fold increased risk of developing diabetes. Basically, if you fail more than one test, your chance of the disease is higher.

But each test is actually assessing a different aspect of diabetes. The fasting glucose is measuring how much glucose your liver is pumping out overnight when you are not eating. A high fasting blood sugar means that your liver is putting out too much glucose, which means it’s not listening to your insulin and, hence, there is insulin resistance at the liver level. The 2-hour post-meal glucose tells you how much the pancreas can ramp up insulin production after you eat; so, it is a measure of pancreatic capacity. Finally, the HbA1c is a measure of glucose sticking onto hemoglobin, and it is reported as a percentage of all your hemoglobin molecules that has glucose stuck on them. This sticking (glycosylation) also happens in the retina and kidneys; therefore, HbA1c tells you about retinal and renal disease. Simply put, each test is probing a different aspect of this complex disease, and the worse you score the worse is your diabetes.

OBJECTIVE

To determine which measures–impaired fasting glucose (IFG), elevated HbA1c, or both–best predict incident diabetes in older adults.

RESEARCH, DESIGN, AND METHODS

From the Health, Aging, and Body Composition study, we selected individuals without diabetes, and we defined IFG (100-125 mg/dL) and elevated HbA1c (5.7-6.4%) per American Diabetes Association guidelines. Incident diabetes was based on self-report, use of antihyperglycemic medicines, or HbA1c ≥6.5% during 7 years of follow-up. Logistic regression analyses were adjusted for age, sex, race, site, BMI, smoking, blood pressure, and physical activity. Discrimination and calibration were assessed for models with IFG and with both IFG and elevated HbA1c.

RESULTS

Among 1,690 adults (mean age 76.5, 46% men, 32% black), 183 (10.8%) developed diabetes over 7 years. Adjusted odds ratios of diabetes were 6.2 (95% CI 4.4-8.8) in those with IFG (versus those with fasting plasma glucose [FPG] <100 mg/dL) and 11.3 (7.8-16.4) in those with elevated HbA1c (versus those with HbA1c <5.7%). When FPG and HbA1c were considered together, odds ratios were 3.5 (1.9-6.3) in those with IFG only, 8.0 (4.8-13.2) in those with elevated HbA1c only, and 26.2 (16.3-42.1) in those with both IFG and elevated HbA1c (versus those with normal FPG and HbA1c). Addition of elevated HbA1c to the model with IFG resulted in improved discrimination and calibration.

CONCLUSIONS

Older adults with both IFG and elevated HbA1c have a substantially increased odds of developing diabetes over 7 years. Combined screening with FPG and HbA1c may identify older adults at very high risk for diabetes.