CLI N IC AL QU ER I ES
Is the A1C reliable? When is the A1C considered unreliable in estimating glycemic control in patients with diabetes? What are the alternatives to using the A1C?—PJ, MAINE Martha Funnell, MS, RN, CDE, replies: Formerly called hemoglobin A1C or glycated or glycosylated hemoglobin, the A1C test is a measure of the percentage of hemoglobin A that’s glycated or has glucose bonded to it. The higher the blood glucose levels, the greater the percentage. Because red blood cells have an average normal lifespan of about 3 months and are constantly being replaced with new ones, the A1C reflects the level of blood glucose during the previous 3 months. Although it’s often described as an average, the results are actually weighted toward the most recent month. Nevertheless, the A1C can be used to estimate the average glucose level.1 Anything that affects the life cycle of the red blood cell can alter A1C results, including more than 700 disorders.2 (See What causes false
What causes false A1C values? 5 These are some of the more common causes. False high values • iron deficiency with or without anemia • a blood transfusion within 3 months • splenectomy • hypertriglyceridemia • hemoglobinopathies, such as sickle cell trait False low values • sickle cell anemia • acute blood loss • thalassemia • chronic liver disease • uremia • antiretroviral therapy.
A1C values?) Although some epidemiologic studies have shown slightly higher readings among certain ethnic groups, primarily Black Americans, A1C is still considered to be clinically appropriate for most patients.1 Because of the efforts of the National Glycohemoglobin Standardization Program, the precision and reliability of A1C results have improved a great deal.2 With current assays, the A1C result can be up to 0.5% higher or lower than the actual percentage. A1C doesn’t measure glucose variability over the course of a day and results aren’t affected by whether the patient is fasting, the most recent blood glucose reading, or recent food intake.3 Lack of consistency between A1C readings and self-monitoring results may be related to the timing of the home blood glucose test and glucose variability. Higher A1C values are more closely related to fasting glucose levels, while readings closer to the normal range are more closely related to postprandial glucose levels.4 Continuous glucose monitoring or more frequent blood glucose monitoring, including pre- and postprandial readings, can be used to better understand unexpected A1C results. Hemoglobin is the glycated protein most often measured because it’s easy to collect and the A1C assays have been standardized, but both fructosamine and glycated albumin levels may be used as short-term measures of glucose control. • Fructosamine is a measure of all serum proteins that undergo glycation, including glycated albumin. Readings can be affected by liver, kidney, or thyroid disease.5 Fructosamine measures aren’t standardized and are rarely used. • Glycated albumin specifically measures the ratio of serum glycated
albumin to total albumin. Both glycated albumin and fructosamine reflect blood glucose levels for the previous 2- to 3-week period. Glycated albumin may be used to measure glucose control among patients with rapid hemoglobin turnover, such as those with chronic kidney disease who are on dialysis or receiving erythropoietin, resulting in unreliable A1C results.5 Many patients think of the A1C as a number their healthcare team uses to make treatment decisions. But this number is also important to patients because it tells them about their risk for long-term complications of diabetes. Nurses should point out that the result isn’t a measure of patients’ selfmanagement efforts, success, or behavior, but the impact of all aspects of their treatment, including medications, on glucose levels. Patients can use the A1C as a guide for sharing in the decision-making process. ■ REFERENCES 1. American Diabetes Association. Standards of medical care in diabetes—2013. Diabetes Care. 2013;36(suppl 1):S11-S66. 2. NGSP. Harmonizing hemoglobin A1C testing. 2010. http://www.ngsp.org. 3. Kuenen JC, Borg R, Kuik DJ, et al. Does glucose variability influence the relationship between mean plasma glucose and HbA1c levels in type 1 and type 2 diabetic patients? Diabetes Care. 2011;34(8):1843-1847. 4. Monnier L, Lapinski H, Colette C. Contributions of fasting and postprandial plasma glucose increments to the overall diurnal hyperglycemia of type 2 diabetic patients: variations with increasing levels of HbA(1c). Diabetes Care. 2003;26(3):881-885. 5. Vos FE, Schollum JB, Coulter CV, Manning PJ, Duffull SB, Walker RJ. Assessment of markers of glycaemic control in diabetic patients with chronic kidney disease using continuous glucose monitoring. Nephrology (Carlton). 2012;17(2):182-188. Martha Funnell is an associate research scientist in the department of medical education at the University of Michigan Medical School in Ann Arbor, Mich. Ms. Funnell is also a member of the Nursing2014 editorial board. Acknowledgment: Supported in part by Grant Number P30DK092926 (MCDTR) from the National Institute of Diabetes and Digestive and Kidney Diseases. The author has disclosed that she has no financial relationships related to this article. DOI-10.1097/01.NURSE.0000446642.80123.22
64 l Nursing2014 l June
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
www.Nursing2014.com
Is the A1C reliable? When is the A1C considered unreliable in estimating glycemic control in patients with diabetes? What are the alternatives to using the A1C?—PJ, MAINE Martha Funnell, MS, RN, CDE, replies: Formerly called hemoglobin A1C or glycated or glycosylated hemoglobin, the A1C test is a measure of the percentage of hemoglobin A that’s glycated or has glucose bonded to it. The higher the blood glucose levels, the greater the percentage. Because red blood cells have an average normal lifespan of about 3 months and are constantly being replaced with new ones, the A1C reflects the level of blood glucose during the previous 3 months. Although it’s often described as an average, the results are actually weighted toward the most recent month. Nevertheless, the A1C can be used to estimate the average glucose level.1 Anything that affects the life cycle of the red blood cell can alter A1C results, including more than 700 disorders.2 (See What causes false
What causes false A1C values? 5 These are some of the more common causes. False high values • iron deficiency with or without anemia • a blood transfusion within 3 months • splenectomy • hypertriglyceridemia • hemoglobinopathies, such as sickle cell trait False low values • sickle cell anemia • acute blood loss • thalassemia • chronic liver disease • uremia • antiretroviral therapy.
A1C values?) Although some epidemiologic studies have shown slightly higher readings among certain ethnic groups, primarily Black Americans, A1C is still considered to be clinically appropriate for most patients.1 Because of the efforts of the National Glycohemoglobin Standardization Program, the precision and reliability of A1C results have improved a great deal.2 With current assays, the A1C result can be up to 0.5% higher or lower than the actual percentage. A1C doesn’t measure glucose variability over the course of a day and results aren’t affected by whether the patient is fasting, the most recent blood glucose reading, or recent food intake.3 Lack of consistency between A1C readings and self-monitoring results may be related to the timing of the home blood glucose test and glucose variability. Higher A1C values are more closely related to fasting glucose levels, while readings closer to the normal range are more closely related to postprandial glucose levels.4 Continuous glucose monitoring or more frequent blood glucose monitoring, including pre- and postprandial readings, can be used to better understand unexpected A1C results. Hemoglobin is the glycated protein most often measured because it’s easy to collect and the A1C assays have been standardized, but both fructosamine and glycated albumin levels may be used as short-term measures of glucose control. • Fructosamine is a measure of all serum proteins that undergo glycation, including glycated albumin. Readings can be affected by liver, kidney, or thyroid disease.5 Fructosamine measures aren’t standardized and are rarely used. • Glycated albumin specifically measures the ratio of serum glycated
albumin to total albumin. Both glycated albumin and fructosamine reflect blood glucose levels for the previous 2- to 3-week period. Glycated albumin may be used to measure glucose control among patients with rapid hemoglobin turnover, such as those with chronic kidney disease who are on dialysis or receiving erythropoietin, resulting in unreliable A1C results.5 Many patients think of the A1C as a number their healthcare team uses to make treatment decisions. But this number is also important to patients because it tells them about their risk for long-term complications of diabetes. Nurses should point out that the result isn’t a measure of patients’ selfmanagement efforts, success, or behavior, but the impact of all aspects of their treatment, including medications, on glucose levels. Patients can use the A1C as a guide for sharing in the decision-making process. ■ REFERENCES 1. American Diabetes Association. Standards of medical care in diabetes—2013. Diabetes Care. 2013;36(suppl 1):S11-S66. 2. NGSP. Harmonizing hemoglobin A1C testing. 2010. http://www.ngsp.org. 3. Kuenen JC, Borg R, Kuik DJ, et al. Does glucose variability influence the relationship between mean plasma glucose and HbA1c levels in type 1 and type 2 diabetic patients? Diabetes Care. 2011;34(8):1843-1847. 4. Monnier L, Lapinski H, Colette C. Contributions of fasting and postprandial plasma glucose increments to the overall diurnal hyperglycemia of type 2 diabetic patients: variations with increasing levels of HbA(1c). Diabetes Care. 2003;26(3):881-885. 5. Vos FE, Schollum JB, Coulter CV, Manning PJ, Duffull SB, Walker RJ. Assessment of markers of glycaemic control in diabetic patients with chronic kidney disease using continuous glucose monitoring. Nephrology (Carlton). 2012;17(2):182-188. Martha Funnell is an associate research scientist in the department of medical education at the University of Michigan Medical School in Ann Arbor, Mich. Ms. Funnell is also a member of the Nursing2014 editorial board. Acknowledgment: Supported in part by Grant Number P30DK092926 (MCDTR) from the National Institute of Diabetes and Digestive and Kidney Diseases. The author has disclosed that she has no financial relationships related to this article. DOI-10.1097/01.NURSE.0000446642.80123.22
64 l Nursing2014 l June
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
www.Nursing2014.com
