Hemoglobin A1cCore Lab Study
Synonym/Acronym
A1c, glycated hemoglobin (Hgb), glycohemoglobin.
Rationale
To identify individuals with diabetes and to monitor treatment in individuals with diabetes by evaluating their long-term glycemic management.
A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.
Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.
Hemoglobin A1c is mainly used to screen and assess for diabetes.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
Method: Capillary electrophoresis
| Normal (without diabetes) | 4.8%–5.6% | | Prediabetes | 5.7%–6.4% | | Values above the range for prediabetes indicate diabetes | Greater than or equal to 6.5% |
|
Values vary widely by method. The recommended treatment goal assumes the use of a standardized test, as referenced to the National Glycohemoglobin Standardization Program—Diabetes Control and Complications Trial, and the absence of clinical conditions such as hemoglobinopathies, anemias, and kidney and liver diseases known to affect the accuracy of the test results.
| Recommended Goals for Monitoring Glycemic Management Using Hgb A1c | A1c% |
|---|
| Children and adolescents (applicable to all ages in the pediatric category; however, goals should be individualized especially for type 1 diabetes, and special consideration should be given to age-related lack of awareness for hypoglycemia when setting less stringent goals) | Less than 7% | | Pregnant females (goals are stricter for pregnant females, especially in the second and third trimesters, related to hemodilution and increased red blood cell [RBC] turnover which has the effect of independently decreasing A1c) | 6%–6.5%; the goal may be relaxed to 7% in order to avoid hypoglycemia | | Nonpregnant adults with or without diabetes who do not experience significant hypoglycemia (see table note) | Less than 7% | | Nonpregnant adults with or without diabetes who do not experience significant hypoglycemia: Using data provided from the Ambulatory Glucose Profile, the goal parallel to less than or equal to 7% | Time in range greater than 70% with time below range less than 4% | | Older adults who are otherwise healthy with good cognitive function and few chronic health issues | Less than 7%–7.5% | | Diabetes (stricter goals are reasonably recommended for certain individuals with diabetes, e.g., those who are otherwise healthy, are newly diagnosed, are type 2 diabetics being treated with lifestyle adjustments and limited oral antidiabetes medications such as metformin to lower glucose levels, have not yet developed complications related to diabetes, do not experience significant hypoglycemia) | 6.5% or less | | Diabetes (less strict goals are reasonably recommended for certain individuals with diabetes, e.g., older adults; those who have been diagnosed with diabetes for a lengthy period of time and have been unsuccessful achieving lower A1c goals; have complications related to diabetes; have one or more comorbidities; have a short life expectancy; are being treated with multiple antidiabetes medications, including insulin, to lower glucose levels; have a documented history of hypoglycemia) | Less than 8% |
Age, blood loss (significant), erythropoietin therapy, ethnicity, hemodialysis, hemoglobinopathies, HIV treatment, pregnancy, and recent blood transfusion are some of the variables that independently affect blood glucose levels, thereby also affecting A1c levels and the approach to glycemic management. A1c goals for persons with diabetes are set and monitored by the health-care provider (HCP) in collaboration with the patient. Goals are based on a variety of factors that include the number of years diagnosed with diabetes, identification of complications related to diabetes, identification of comorbidities, evidence of hypoglycemia, life expectancy based on risk factors, recommended therapies, ability to access resources required to support the treatment plan, level of available and dependable support (e.g., for pediatric patients, patients with language barriers, or patients with intellectual, emotional, or physical impairments). Summarized from American Diabetes Association. Standards of Medical Care in Diabetes. (2022). Diabetes Care, 45(Suppl. 1):S83-S96. |
Study type: Blood collected in a lavender-top [EDTA] tube; related body system: Circulatory and Endocrine systems.
Hgb A1c, also known as glycosylated or glycated Hgb, is the combination of glucose and Hgb into a ketamine; the rate at which this occurs is proportional to glucose concentration. The average life span of an RBC is approximately 120 days; measurement of glycated Hgb is a way to monitor long-term diabetic management. A change of 1% in the A1c is roughly equivalent to a change in glucose concentration of 29 mg/dL or 1.6 mmol/L. The average plasma glucose can be estimated using the formula (mg/dL) 
= [(A1c × 28.7) - 46.7].
The same formula can be used to convert the estimated average glucose (eAG) to glucose in SI units (after multiplying the eAG by 0.555 to convert from mg/dL to mmol/L).
For example, an A1c value of 6% would reflect an average plasma glucose of 125.5 mg/dL, or [(6 × 28.7) – 46.7]. Expressed in SI units, [(6 × 28.7) – 46.7] = 125.5 × 0.555 = 7 mmol/L.
Hgb A1c levels are not age dependent and are not affected by exercise, diabetic medications, or nonfasting state before specimen collection. The Hgb A1c assay would not be useful for patients with hemolytic anemia, abnormal Hgb (e.g., Hgb S), or abnormal RBC turnover (e.g., sickle cell disease, pregnancy, hemodialysis, recent blood loss, recent blood transfusion, erythropoietin therapy). These patients would be screened, diagnosed, and managed using symptoms, clinical risk factors, short-term glycemic indicators (glucose), intermediate glycemic indicators (1,5-anhydroglucitol or glycated albumin), and longer-term glycemic indicators (fructosamine).
Diabetes is a group of diseases characterized by hyperglycemia, or elevated glucose levels. Hyperglycemia can result from a defect in insulin secretion due to destruction of the beta cells of the pancreas (type 1 diabetes), a defect in insulin action, or a combination of defects in secretion and action (type 2 diabetes), or from a specific cause such as gestational diabetes, neonatal hyperglycemia, cystic fibrosis, post–organ transplantation, or hyperglycemia induced by drugs used to treat other medical conditions (e.g., antiretrovirals, corticosteroids). The chronic hyperglycemia of diabetes over time may lead to damage, dysfunction, and eventually failure of the eyes (retinopathy), kidneys (nephropathy), nerves (neuropathy), heart (cardiovascular disease), and blood vessels (micro- and macrovascular conditions). For additional information regarding screening guidelines and management of diabetes, refer to the study titled “Glucose, Core Lab Study.” The American Diabetes Association (ADA) and National Institute of Diabetes and Digestive and Kidney Disease (NIDDK) have established criteria for diagnosing diabetes.
The 2019 American College of Cardiology (ACC) and American Heart Association (AHA) guidelines for the prevention of cardiovascular disease and the 2022 American Diabetes Association (ADA) recommendations regarding diabetes self-management education and support suggest these topics be included in the patient–HCP conversation along with assessment of evidence-based risk factors in order to better and more realistically improve diabetes and cardiovascular disease health outcomes. Especially important are patient concerns that result in cost-related medication nonadherence to treatment.
| Diagnostic Criteria for Diabetes in the Absence of Classic Symptoms of Hyperglycemia*: Any Two of the Following Three Findings: |
|---|
| Glucose | Conventional Units | SI Units (Conventional Units × 0.0555) |
|---|
| 1.Fasting plasma glucose | Equal to or greater than 126 mg/dL | Equal to or greater than 7 mmol/L | | 2.2-hr post-challenge plasma glucose with standardized 75-mg load | Greater than 200 mg/dL | Greater than 11.1 mmol/L | | 3.A1c | 6.5% or greater | 6.5% or greater | | OR | | Random plasma glucose in the presence of classic symptoms of hyperglycemia or a hyperglycemic crisis | Greater than 200 mg/dL | Greater than 11.1 mmol/L |
|
Continuous Glucose Monitoring and the Ambulatory Glucose Profile
Continuous glucose monitoring (CGM) has become a technology frequently used to monitor and successfully manage diabetes. The Ambulatory Glucose Profile (AGP) was developed by the International Diabetes Center. It is a one-page report of in-vivo glucose data that can be generated by most CGM monitors and is recognized as the standard of care for reporting CGM data by the ADA. The program converts glucose readings into simple, easy-to-understand, color-coded graphs that cover seven or more days of data showing:
- Average glucose
- Variability of glucose levels
- Graphs across a 24-hr period
- Daily glucose patterns where different colors also show periods of hypoglycemia and hyperglycemia
- Graphs across a longer period of time
- Time in range: the amount of time in range as well as the time above and below the target range. This information can be useful in evaluating changes in treatment. It also correlates well with the target or predicted hemoglobin A1c
- Note: The data from the AGP that parallels the Hemoglobin A1c target of less than 7% is: Time in range greater than 70% with time below less than 4%
The AGP report is identical in how it looks and presents the data regardless of the type of CGM system being used. However, the report generated by some systems may vary in the total number of glucose data points used to generate the statistics (e.g., the International Diabetes Center report includes 90% of glucose values and another system might use 80% of the glucose data point.
Assist in the diagnosis of diabetes and assess long-term management of glucose levels in individuals with diabetes.
- Assist in the diagnosis of diabetes and prediabetes in patients with HIV before starting antiretroviral therapy, at the time antiretroviral therapy is changed, and 36 months after antiretroviral therapy is initiated or changed.
- Note: The hemoglobin A1c test is not recommended to screen for cystic fibrosis related diabetes (CFRD). For additional information related to testing for CFRD see the studies titled, “Chloride, Sweat” and Glucose Tolerance Tests.”
Factors That May Alter the Results of the Study
- Drugs and other substances that may increase glycated Hgb values include albuterol, anesthetics, anticonvulsants, antidepressants (tricyclic), antifungals, antipsychotics, antiretrovirals, beta blockers (atenolol, propranolol), calcium channel blockers, corticosteroids (corticotropin, cortisone, dexamethazone, prednisone), cyclosporins, diuretics (loop, thiazides, triamterene), epinephrine, ethacrynic acid, glucagon, immunosuppressants, isoniazid, IV solutions containing dextrose, octreotide, oral contraceptives, niacin, somatotropin, TB medications, and thyroid hormone.
- Drugs and other substances that may decrease glycated Hgb values include antidiabetic drugs (acarbose, albiglutide, alogliptin, canagliflozin, chlorpropamide, dapagliflozin, dulaglutide, empagliflozin, exenatide, glimepiride, gliclazide, glipizide, glyburide, insulins, linagliptin, liraglutide, metformin, miglitol, nateglinide, pioglitazone, repaglinide, rosiglitazone, saxagliptin, sitagliptin), antiretroviral drugs, and drugs that cause RBC hemolysis (e.g., dapsone).
- Conditions that affect the reliability of glycated Hgb values. In these situations only plasma glucose criteria should be used to diagnose diabetes.
- Abnormal Hgb (hemoglobinopathies such as sickle cell disease)
- Blood loss (recent)
- Blood transfusion (recent)
- Erythropoietin therapy
- Hemodialysis
- Hemolytic anemias (e.g., glucose-6-phosphate dehydrogenase deficiency)
- HIV
- Pregnancy (second trimester, when screening for gestational diabetes usually occurs, through the postpartum period)
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assist in evaluating blood sugar management over approximately the past 3 mo.
- Explain that a blood sample is needed for the test.
After the Study: Implementation & Evaluation Potential Nursing Actions
Avoiding Complications
- Discuss how good management of glucose levels delays the onset and slows the progression of diabetic retinopathy, nephropathy, and neuropathy.
- Explain that unmanaged diabetes can cause multiple health issues, including diabetic kidney disease, amputation of limbs, and ultimately in death.
Treatment Considerations
- Studies comparing risk for developing diabetes demonstrate that certain populations are disproportionately affected by type 2 diabetes and complications of type 2 diabetes as compared to the general population.
- Nonmodifiable risk factors include age, ethnicity, and family history of diabetes or metabolic syndrome.
- Modifiable risk factors include lifestyle choices related to making healthy dietary choices, maintaining a healthy body weight, and meeting recommended levels of physical activity.
- Risk of developing type 2 diabetes increases with age.
- In the United States, affected populations include African Americans, Asian Americans, Hispanics, native Hawaiians and Pacific Islanders, American Indians, and Alaska natives.
- A system for the prevention, management, and support of patients with type 2 diabetes should be provided through the coordinated efforts of multidisciplinary partners using strategies that are culturally appropriate.
- Instruct the patient in the use of continuous glucose monitoring systems; home testing strips or meters approved for glucose, ketones, or A1c by the U.S. Food and Drug Administration, if prescribed.
- Discuss the importance of reporting signs and symptoms of hypoglycemia (weakness, confusion, diaphoresis, rapid pulse) or hyperglycemia (thirst, polyuria, hunger, lethargy).
- Monitor blood glucose results and administer ordered insulin or oral antihyperglycemic drugs.
- Assess the cultural aspects of diet selection.
- Correlate dietary intake with blood glucose.
Nutritional Considerations
- Increased levels of Hgb A1c may be associated with diabetes. There is no “diabetic diet”; however, many meal-planning approaches with nutritional goals are endorsed by the ADA.
- Patients who adhere to dietary recommendations report a better general feeling of health, better weight management, better management of glucose and lipid values, and improved use of insulin.
- Discuss the nutritional management of diabetes.
- Explain that a variety of dietary patterns are beneficial for people with diabetes.
- Encourage consultation with a registered dietitian who is a certified diabetes educator.
- Numerous studies point to the prevalence of excess body weight in American children and adolescents. Findings from the 2017–2020 National Health and Nutrition Examination Survey (NHANES), regarding the prevalence of obesity in younger members of the population, estimate that obesity is present in 12.7% of the population ages 2 to 5 yrs, 20.5% ages 6 to 11 yrs, and 22.2% ages 12 to 19 yrs. The medical, social, and emotional consequences of excess body weight are significant. Special attention should be given to instructing the pediatric patient and caregiver regarding health risks and weight control education. For adults age 20 and over the prevalence of obesity is 41.9%.
- The Centers for Disease Control and Prevention (CDC) defines obesity as body mass index (BMI) at or above the 95th percentile for CDC gender-specific BMI by age growth charts.
Clinical Judgement
- Consider which approach to glucose management is the best fit based on a careful cultural assessment.
Follow-Up and Desired Outcomes
- Acknowledges contact information provided for the ADA (www.diabetes.org), American Heart Association (www.heart.org/HEARTORG), National Heart, Lung, and Blood Institute (www.nhlbi.nih.gov), NIDDK (www.niddk.nih.gov), and U.S. Department of Agriculture’s resource for nutrition (www.choosemy plate.gov).
- Understands that the ADA recommends A1c testing four times a year for insulin-dependent type 1 or type 2 diabetes when glycemic targets are not being met or when therapy has changed and twice a year when treatment goals are being met for non–insulin-dependent type 2 diabetes. The ADA also recommends that testing for diabetes commence at age 35 for asymptomatic individuals; be considered for adults of any age who are overweight and have additional risk factors, and continue every 3 yr in the absence of symptoms; be performed on patients with HIV, in relation to the timing of therapeutic interventions; be performed annually on patients with prediabetes; be performed every 3 yr (lifelong) for patients diagnosed with gestational diabetes.
- Adheres to the request for periodic A1c laboratory studies to better manage the disease process over time.