![]() Thus, as suggested, a patient's SMBG or CGM profile has considerable potential for optimizing his or her glycemic management ( 5).įor many people with diabetes, glucose monitoring is key for achieving glycemic targets. In a recent report, mean glucose measured with CGM versus central laboratory–measured A1C in 387 participants in three randomized trials demonstrated that A1C may underestimate or overestimate mean glucose in individuals ( 5). Clinicians should note that the mean plasma glucose numbers in Table 6.1 are based on ∼2,700 readings per A1C in the ADAG trial. The American Diabetes Association (ADA) and the American Association for Clinical Chemistry have determined that the correlation ( r = 0.92) in the ADAG trial is strong enough to justify reporting both the A1C result and the estimated average glucose (eAG) result when a clinician orders the A1C test. Table 6.1 shows the correlation between A1C levels and mean glucose levels based on the international A1C-Derived Average Glucose (ADAG) study, which assessed the correlation between A1C and frequent SMBG and CGM in 507 adults (83% non-Hispanic Whites) with type 1, type 2, and no diabetes ( 6), and an empirical study of the average blood glucose levels at premeal, postmeal, and bedtime associated with specified A1C levels using data from the ADAG trial ( 7). Though some variability in the relationship between average glucose levels and A1C exists among different individuals, generally the association between mean glucose and A1C within an individual correlates over time ( 5). are accurate in individuals heterozygous for the most common variants (see Other measures of average glycemia such as fructosamine and 1,5-anhydroglucitol are available, but their translation into average glucose levels and their prognostic significance are not as clear as for A1C and CGM. Hemoglobin variants must be considered, particularly when the A1C result does not correlate with the patient's CGM or SMBG levels. For example, conditions that affect red blood cell turnover (hemolytic and other anemias, glucose-6-phosphate dehydrogenase deficiency, recent blood transfusion, use of drugs that stimulate erythropoesis, end-stage kidney disease, and pregnancy) may result in discrepancies between the A1C result and the patient's true mean glycemia. Although A1C variability is lower on an intraindividual basis than that of blood glucose measurements, clinicians should exercise judgment when using A1C as the sole basis for assessing glycemic control, particularly if the result is close to the threshold that might prompt a change in medication therapy. As with any laboratory test, there is variability in the measurement of A1C. The A1C test is an indirect measure of average glycemia and, as such, is subject to limitations. ![]() Unstable or intensively managed patients or people not at goal with treatment adjustments may require testing more frequently (every 3 months with interim assessments as needed) ( 4). Patients with type 2 diabetes with stable glycemia well within target may do well with A1C testing or other glucose assessment only twice per year. The use of point-of-care A1C testing may provide an opportunity for more timely treatment changes during encounters between patients and providers. The frequency of A1C testing should depend on the clinical situation, the treatment regimen, and the clinician's judgment. Measurement approximately every 3 months determines whether patients' glycemic targets have been reached and maintained. Thus, A1C testing should be performed routinely in all patients with diabetes at initial assessment and as part of continuing care. The performance of the test is generally excellent for National Glycohemoglobin Standardization Program (NGSP)-certified assays (see The test is the primary tool for assessing glycemic control and has strong predictive value for diabetes complications ( 1– 3). A1C reflects average glycemia over approximately 3 months.
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