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A1C Shows Predictive Advantage
March 5, 2010
The HbA1c test can more accurately identify people at risk for a variety of health conditions than the fasting plasma glucose test, according to new research from the Johns Hopkins Bloomberg School of Public Health. This finding comes on the heels of a decision by the American Diabetes Association to include HbA1c as an official screening test for diagnosing diabetes and detecting prediabetes.
The HbA1c (or A1C) test, which involves having a small amount of blood drawn, looks at the concentration of red blood cells that have glucose molecules attached, reflecting the concentration of glucose in the blood. Because the red blood cells found in any blood sample are a mixture of cells of different ages, the HbA1c test gives a “weighted” average of blood glucose control over the previous 2–3 months. The fasting plasma glucose test screens for diabetes by measuring the concentration of glucose in a person’s blood after at least eight hours without food or drink.
The researchers checked HbA1c levels in blood samples that had been collected between 1990 and 1992 from people at four centers in Maryland as part of the Atherosclerosis Risk in Communities (ARIC) Study. The samples were collected from 11,092 African-American and white adults who did not have a history of diabetes. Fasting plasma glucose levels were determined from participants’ medical records. The researchers evaluated the results from both tests in light of health conditions the study subjects developed during 15 years of follow-up in the ARIC Study.
The greatest number of participants had HbA1c levels between 5.0% and 5.5% at the start of the study. The researchers found that with each incremental increase in HbA1c came an increased incidence in diabetes during the follow-up period. The participants’ incidences of coronary heart disease and stroke also showed a significant association with their HbA1c levels. In comparison, while fasting glucose level results showed a similar ability to HbA1c for predicting future diabetes, they were not associated with rates of coronary heart disease or stroke in people whose baseline HbA1c levels were below 6.0%.
According lead study author Elizabeth Selvin, PhD, MPH, “HbA1c has significant advantages over fasting glucose. The A1C test has low variability from day to day, levels are not affected by stress and illness, it has greater stability, and the patient is not required to fast before the test is performed.”
To learn more, read the article “Hemoglobin A1c Outperforms Fasting Glucose for Risk Prediction” or see the study’s abstract in The New England Journal of Medicine.
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