https://diabetes.acponline.org/archives/2014/06/13/3.htm

HbA1c levels appear to be higher in older patients

HbA1c levels appear to increase as patients age, independent of glucose levels and insulin resistance, according to a new study.


HbA1c levels appear to increase as patients age, independent of glucose levels and insulin resistance, according to a new study.

Researchers used data from the Screening for Impaired Glucose Tolerance (SIGT) study and the National Health and Nutrition Examination Survey (NHANES) to perform a cross-sectional analysis examining HbA1c level and age. The study's objectives were to investigate whether age differences in HbA1c could affect diabetes screening and management; whether age effects were related to unrecognized diabetes and prediabetes, insulin resistance, or postprandial hyperglycemia; and whether age affects the diagnostic accuracy of HbA1c. The results were published online June 5 by Diabetic Medicine.

A total of 1,573 patients who participated in the SIGT study from 2005 to 2008 and 1,184 patients who participated in NHANES from 2005 to 2006 were included in the current analysis. Mean age was similar in both studies (48 years in the SIGT study vs. 47 years in NHANES). In the SIGT study, 58% of patients were black and 58% were women, while 32% of patients were black and 46% were women in NHANES.

In univariate analyses, the authors found that glucose intolerance and HbA1c levels both increased with age, by 0.085% per 10 years in the SIGT study and 0.094% per 10 years in NHANES. In all patients from both studies, HbA1c increased 0.08% per 10 years in patients without diabetes and 0.07% per 10 years in patients whose glucose tolerance was normal (P<0.001 for all comparisons). In multivariate analyses that included patients with normal glucose tolerance, a statistically significant relationship remained between age and HbA1c level (P<0.001) after adjustment for race, body mass index, waist circumference, fasting and 2-hour plasma glucose levels, and other variables. In addition, as age increased, the specificity of HbA1c criteria for diagnosing prediabetes decreased significantly (P<0.0001).

The authors noted that they were unable to evaluate the effects of kidney function and anemia and that their results may not be generalizable to all patients, among other limitations. However, they concluded that based on their results, increasing age is associated with increasing HbA1c levels, and the association cannot be solely attributed to age-related increases in insulin resistance, postprandial hyperglycemia, and insulin resistance. They also pointed out that the effect of age is clinically significant, estimating that an 80-year-old patient with normal glucose tolerance would have an HbA1c level 0.35% greater than a 30-year-old patient with normal glucose tolerance and the same glucose levels.

“While underlying mechanisms need further study, age differences should be taken into consideration when using HbA1c for the diagnosis, screening and management of diabetes and prediabetes, and for comparisons of provider and healthcare system performance,” the authors wrote.