According to the American Diabetes Association (ADA) there were 34.2 million Americans (over 10% of the population) living with diabetes in 2018 and approximately 1.5 million Americans are diagnosed with diabetes every year (ADA, 2020). For patients with diabetes, controlling glucose levels is critical in preventing long term complications. Nurses must possess a clear understanding of the variety of ways that blood glucose can be measured as we play an integral role in educating our patients about their diabetes and how to monitor it. In this blog, we will focus on hemoglobin A1C, what it is, and why it’s important.
Fingerstick blood glucose and continuous glucose monitoring are common methods that provide instant results allowing clinicians and patients with diabetes to make decisions on glucose management and insulin dose selection before meals and throughout the day (Selvin, 2020). It is a snapshot of a patient’s glucose level at a specific point in time. Glycated hemoglobin (A1C, hemoglobin A1C, HbA1c) is a clinical blood test that estimates mean blood glucose over a two-to-three-month timeframe. While the test has been around for decades, it was finally recognized in 2010 by the ADA as a tool to diagnose diabetes and prediabetes (Dugger & Clark, 2011) and has become the most routinely used test to monitor chronic glycemic control (Selvin, 2020). The American Association of Clinical Endocrinologists and the American College of Endocrinology recommend that the A1C should be used in conjunction with other criteria such as fasting plasma glucose (FPG) and/or oral glucose tolerance tests (OGTTs) when diagnosing diabetes (Hill & Appel, 2010).
What Exactly Does A1C Measure?
When we eat, glucose enters the bloodstream and as it builds up, it binds to hemoglobin in the red blood cells creating glycated (or glycosylated) hemoglobin. Red blood cells live for approximately three months so A1C can reflect the average plasma glucose over the previous 90 days. It is a reliable, rapid test that does not require the patient to fast and can help differentiate a stress-induced hyperglycemia from a chronic or sustained hyperglycemia found in diabetes (Dugger & Clark, 2011). For people without diabetes, the normal range for A1C level is between 4% and 5%. An A1C level between 5.7% and 6.4% is considered prediabetes, indicating the patient is at a high risk of developing diabetes in the future. A level greater than 6.5% is considered diabetes. For patients with diabetes, the typical goal is to maintain the A1C level below 7%, as levels consistently higher than 8% may lead to long term complications.
||Fasting Plasma Glucose (mg/dL)
||4 - 5%
||Less than or equal to 99
||5.7 - 6.4%
||100 - 125
||Greater than or equal to 6.5%
||Greater than or equal to 126
Conditions that affect A1C values (Selvin, 2020)
Any condition that impacts the life cycle of the red blood cell will affect A1C results. If red blood cell turnover is low, there may be a disproportionate number of older red cells, causing a falsely high A1C value. Vitamin B12 or folate deficient anemia can cause low red cell turnover. However, with rapid cell turnover, there are a larger number of young red cells that are not bound to glucose, resulting in a falsely low A1C value. Conditions that can cause a rapid cell turnover include chronic hemolysis (i.e., thalassemia); patients treated for iron, vitamin B12, or folate deficiency; and patients treated with erythropoietin.
A1C alone may not be helpful in patients who have experienced recent blood loss, hemolytic anemia, hemoglobinopathies (i.e., sickle cell trait), severe hepatic and renal disease or frequent hypoglycemic events (Dugger & Clark, 2011). A1C is not recommended for diagnosing type 1 diabetes or gestational diabetes. In addition, it’s important to note that there are several genetic variants in hemoglobin that may be found in African American, Hispanic American, and Asian American populations. A1C testing may have limitations in these patient groups however most modern lab tests are no longer affected by common hemoglobin variants (Selvin, 2020).
A valuable tool used in the primary care setting, A1C can help guide medication and diet regimens in the management of glycemic control for patients with diabetes and assess the efficacy of those treatments. A1C is also recommended in hospitalized patients if a result is not available from the prior 2 to 3 months (Dugger & Clark, 2011) as early identification will help improve patient outcomes.
American Diabetes Association (2018). Statistics About Diabetes. https://www.diabetes.org/resources/statistics/statistics-about-diabetes
Dugger, L., & Clark, A. P. (2011). Can hemoglobin A1c testing in hospital settings help the early identification of diabetes?. Clinical nurse specialist CNS, 25(4), 171–175. https://doi.org/10.1097/NUR.0b013e318222a693
Hill, A. N., & Appel, S. J. (2010). Diagnosing diabetes with A1C: implications and considerations for measurement and surrogate markers. The Nurse practitioner, 35(10), 16–24. https://doi.org/10.1097/01.NPR.0000388206.16357.02
Selvin, E. (2020, December 4). Measurements of glycemic control in diabetes mellitus. UpToDate. https://www.uptodate.com/contents/measurements-of-glycemic-control-in-diabetes-mellitus