than those from the first 60 days. The more significant the amount of glycation present, the higher the A1C. Conditions that cause rapid turnovers of red blood cells, such as traumatic blood loss, chronic kidney disease, sickle cell disease, recent blood transfu- sions, or erythropoietin therapy, can interfere with A1C test ac- curacy. People with diabetes have higher A1C levels compared to people without diabetes. There is a strong relationship between high A1C levels and the risk of developing diabetes-related com- plications, including cardiovascular disease, retinopathy, and neu- ropathy. Most laboratories in the U.S. report A1C levels per the National Glycohemoglobin Standardization Program (NGSP). Average val- ues are standardized to the Diabetes Control and Complications Trial (DCCT) Research Group results. In persons without diabetes, the average A1C value ranges between 4 and 6 percent. In 2010, A1C levels were used as one criterion for diabetes. The ADA rec- ommends monitoring A1C levels at least twice per year for well- managed diabetes and quarterly when patients are not achieving glycemic targets. Estimated average glucose (EAG) levels Patients often have difficulty understanding the relationship be - tween blood glucose levels and their A1C levels. The estimated average glucose (eAG) level can be used to quantify A1C levels in more familiar terms that closely represent daily blood glucose readings. Introduced by the ADA in 2010, any A1C level can be converted to an eAG by using the formula eAG = 28.7 × A1C – 46.7. For example, if a patient has an A1C level of 8.2, the health care provider can use the eAG conversion formula and show the patient their average blood glucose level is 189 mg/dL. Table 5 provides the estimated AG levels for A1C test results. Self-Assessment Quiz Question #4 An A1C of 9.2% correlates with a mean plasma blood glucose of:
A1C testing and daily blood glucose monitoring provide useful in- formation in the management of diabetes, but they are expressed in different ways. Daily blood glucose monitoring via a glucom- eter directly measures the amount of glucose in the blood at the time the sample is taken and is expressed as milligrams of glucose per deciliter of blood (e.g., 154 mg/dL). A1C also uses a blood sample, but it looks at the percentage of hemoglobin, a protein in red blood cells that has attached to glucose (e.g., 7.0 percent). Evidence-Based Practice: An appropriate A1C goal for non- pregnant adults without a limited life expectancy is <7.0% (53 mmol/mol) without significant hypoglycemia. Less stringent A1C goals (e.g., <8.0%; 64 mmol/mol) may be appropriate for older persons or those with limited life expectancy, or where the harms of treatment are greater than the benefits. Health care providers must work with patients and consider adjusting glycemic targets to ensure safety and limit adverse effects 3 .
Table 5. Estimated Average Glucose (eAG) Levels A1C (%) mg/dL mmol/L 5 97 (76 to 120)
5.4 (4.2 to 6.7)
6 7 8 9
126 (100 to 152) 154 (123 to 185) 183 (147 to 217) 212 (170 to 249) 240 (193 to 282) 269 (217 to 314) 298 (240 to 347)
7.0 (5.5 to 8.5) 8.6 (6.8 to 10.3) 10.2 (8.1 to 12.1) 11.8 (9.4 to 13.9) 13.4 (10.7 to 15.7) 14.9 (12.0 to 17.5) 16.5 (13.3 to 19.3)
10 11 12
Adapted from American Diabetes Association3.
a. 167 mg/dL. b. 195 mg/dL. c. 217 mg/dL. d. 257 mg/dL.
Measuring blood glucose levels with point-of-care testing (POCT) A1C and blood glucose levels are usually calculated in a labora- tory using venous blood. Results are generally standardized to NGSP methodology and are reliable estimates of glycemic mea- sures, referred to as central laboratory testing (CLT). Because it may take 24 hours or longer to obtain the results, neither the patient nor the health care provider has access to current glyce- mic measures during a patient’s appointment. For this reason, it is becoming increasingly common in outpatient settings to use point-of-care testing (POCT), which analyzes a capillary sample in
a desktop analyzer. The standard of care is teaching anyone doing POCT the importance of quality control with procedure. POCT of blood glucose levels is widely used in hospitals and pri- mary care settings to provide rapid results and facilitate the timely treatment of hypoglycemia and hyperglycemia as well as in-office decision making related to medications and glycemic manage- ment. POCT should not be used for diagnosing diabetes 14 .
Case study 2 Joan is a 57-year-old Hispanic female with a history of type 2 dia- betes for 10 years. Her BMI is 29.0, and she has stage 1 hyper- tension. Her medication regimen includes glipizide 20 mg daily; metformin 1,000 mg twice daily; and chlorthalidone 25 mg daily. Joan’s A1Cs have been 8.4% and 9.2% in the past year. Joan states that she feels tired but otherwise is well. After Joan was di- agnosed with type 2 diabetes, she learned how to test her blood glucose but has not done so in the last couple of years. Joan ac- knowledges that she has not felt confident performing blood glu - cose monitoring (BGM). She states her healthcare provider never asks her about testing her blood glucose or seeing her logbook. Questions 1. How would you interpret the A1C results? 2. Would you recommend BGM for Joan? 3. What additional support would be appropriate for Joan?
Discussion 1.
Joan’s A1C results indicate her glycemic goals are not in the range recommended by the American Diabetes Association (ADA). During the last year, two A1C levels were done. Because neither of Joan’s A1C values were in the target range of less than 7.0%, her A1C levels should be assessed quarterly. 2. Joan would likely benefit from BGM along with attending diabetes education classes. Performing BGM provides data that illustrate how food, physical activity, and medication use affects blood glucose levels. Blood glucose meters have evolved over the 10 years since Joan was diagnosed and selecting a new one that will meet her individual needs is important. To choose the best blood glucose meter for her, consideration should be given to Joan’s preferences;
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