The most recent update of the American Diabetes Association’s (ADA) Standards of Medical Care in Diabetes includes primarily minor changes in treatment recommendations. The most striking developments within the update are found in the section on diagnosis, which adds a third blood test to the two already used for screening—fasting plasma glucose (FPG) and the oral glucose tolerance test (OGTT).
The third method—the hemoglobin (Hb) A1c test—measures the percentage of hemoglobin bound to glucose. This percentage represents plasma glucose levels over the prior three months. HbA1c values have long been used to monitor glycemic control and to estimate a person’s risk of diabetes complication.
“It’s an advance insofar the screening of patients will be made more convenient: [blood samples] needn’t be obtained while the patient is fasting,” says Silvio Inzucchi, MD, director of the Yale Diabetes Center in New Haven, Conn., and chairman of the committee that wrote the update.
In addition, Dr. Inzucchi points out, HbA1c is more stable from day to day: It is not influenced by perturbations like acute illness that could falsify FPG and OGTT, and unlike the other tests, HbA1c readings remain accurate even when processing is delayed.
Screening and diagnosis
Like previous versions, the update recommends screening for all individuals aged 45 years and older and overweight patients (BMI ≥25) with one or more additional risk factors. These risk factors include physical inactivity, hypertension, low HDL (<35 mg/dL) or elevated triglyceride levels (>250 mg/dL), positive family history, and (for women) polycystic ovary syndrome.
Overweight individuals of Latino, African American, Asian American, or Pacific Islander ethnicity should be screened with or without other risk factors, as should women who have delivered a baby weighing >9 lb.
The threshold for a diagnosis of diabetes is FPG ≥126 mg/dL, or two-hour plasma glucose ≥200 mg/dL during OGTT. With the HbA1c test, the threshold is 6.5%. Not infrequently, readings are abnormal for one test but not another. “The ADA decided to go with the more abnormal test when tests are discordant, as long as it is repeated and the results confirmed,” explains Dr. Inzucchi.
A test reading that is elevated but below the threshold for diabetes, traditionally described as “prediabetes,” is also called “increased risk for diabetes” in the update; it suggests heightened risk of cardiovascular disease (CVD) as well. The ranges are 100-125 mg/dL on FPG, two-hour glucose of 140-199 mg/dL on OGTT, and 5.7%-6.4% on HbA1c.
Patients testing at these levels should be rescreened every year and counseled to incorporate lifestyle changes to prevent or delay diabetes. Such changes include losing 5%-10% of body weight (for those who are overweight) and adhering to the same physical activity and nutrition guidelines recommended for diabetes.
Metformin should be considered for those persons at “very high risk”—that is prediabetic individuals younger than age 60 years who are obese and whose HbA1c results are >6%, and who have hypertension, low HDL or high triglycerides, or family history of diabetes.