From the Guidelines
Hemoglobin A1c can be checked at any time of day, regardless of fasting status or recent food intake, as it measures average blood sugar levels over the past 2-3 months. Unlike blood glucose tests that require fasting, the A1c test is not affected by short-term fluctuations caused by eating, making it convenient for patients who can have their blood drawn at any time without special preparation 1. The test works by measuring the percentage of hemoglobin proteins in your blood that have glucose attached to them. Since red blood cells typically live for about 120 days, the A1c provides a longer-term picture of your glucose control rather than a single point-in-time measurement.
Key Points to Consider
- The American Diabetes Association recommends checking A1c every 3-6 months depending on how well controlled your diabetes is and whether your treatment has changed recently 1.
- The target A1c for most adults with diabetes is less than 7%, though individual goals may vary based on age and other health conditions 1.
- It's essential to note that A1c measurement has some limitations, including low sensitivity, possible racial disparities, and interference by anemia and some medications 1.
- For people with diabetes, A1c testing is a crucial tool for assessing glycemic control and adjusting treatment plans accordingly.
Clinical Implications
- The convenience of A1c testing, which does not require fasting, makes it an attractive option for patients.
- However, it's crucial to consider the limitations of A1c testing and use it in conjunction with other measures of glycemic control, such as continuous glucose monitoring (CGM) or self-monitoring of blood glucose (SMBG) 1.
- Healthcare providers should individualize A1c targets based on patient characteristics, such as age, comorbidities, and risk of hypoglycemia.
From the Research
Hemoglobin A1c Testing
- The International Expert Committee recommends that the diagnosis of diabetes be made if hemoglobin A1c (HbA1c) level is greater than or equal to 6.5% and confirmed with a repeat HbA1c test 2.
- HbA1c testing has the advantages of greater clinical convenience, preanalytic stability, and assay standardization, but when used as the sole diagnostic criterion for diabetes, it has the potential for systematic error 2.
- Factors that may not be clinically evident impact HbA1c test results and may systematically raise or lower the value relative to the true level of glycemia, therefore HbA1c should be used in combination with plasma glucose determinations for the diagnosis of diabetes 2.
Fasting vs Random Blood Testing
- There is no specific recommendation for checking HbA1c levels in fasting or random blood samples, however, it is recommended to use HbA1c in combination with plasma glucose determinations for the diagnosis of diabetes 2.
- Fasting plasma glucose, 2-hour postglucose-load plasma glucose, and oral glucose tolerance tests are recommended for the diagnosis of diabetes only if HbA1c testing is not possible due to unavailability of the assay, patient factors that preclude its interpretation, and during pregnancy 2.
- HbA1c or glycated albumin (GA) results from the glycation of hemoglobin or serum albumin and represents 2-month or 2-week glycemia, respectively, and can be used to assess glycemic control 3.
Glycemic Control
- The clinical goal of diabetes management is a good quality of life that is not different from that of healthy subjects, and to fulfill this goal, prevention of complications is needed under good glycemic control 3.
- HbA1c is the gold standard measurement for the assessment of glycemic control, and worldwide large-scale clinical studies of diabetes complications have greatly valued HbA1c as an indicator of glycemic control 3.
- The correction of postprandial hyperglycemia is one of the important goals of glycemic control to prevent cardiovascular disease 3.