What is the significance of Hemoglobin A1c (HbA1c)?

From the Guidelines

HbA1c is a crucial blood test that measures average blood glucose levels over the past 2-3 months, making it the gold standard for long-term diabetes monitoring, with a target goal of less than 7% for most nonpregnant adults, as recommended by the American Diabetes Association standards of medical care in diabetes 1.

Significance of HbA1c

The test works by measuring the percentage of hemoglobin proteins in red blood cells that have glucose attached to them. For people without diabetes, normal HbA1c levels typically range from 4% to 5.6%. Prediabetes is indicated by levels between 5.7% and 6.4%, while diabetes is diagnosed when levels reach 6.5% or higher.

HbA1c Goals and Limitations

• The HbA1c goal for most nonpregnant adults is less than 7% (Appendix Table) 1.
• Providers might suggest more stringent HbA1c goals (such as <6.5%) for selected patients, such as those with short duration of diabetes, long life expectancy, or no cardiovascular disease 1.
• Less stringent HbA1c goals (such as <8%) may be appropriate for patients with a history of severe hypoglycemia, limited life expectancy, advanced microvascular or macrovascular complications, extensive comorbid conditions, or long-standing diabetes, in whom the goal is difficult to achieve despite diabetes self-management education, appropriate glucose monitoring, and intensive insulin therapy 1.
• HbA1c testing has limitations, including conditions that affect erythrocyte turnover (hemolysis or blood loss) and hemoglobin variants, which must be considered when the HbA1c result does not correlate with the patient's blood glucose levels 1.

Clinical Implications

• The test's significance lies in its ability to predict diabetes complications—each 1% reduction in HbA1c correlates with approximately 25-35% decreased risk of microvascular complications like retinopathy, nephropathy, and neuropathy 1.
• Unlike daily glucose monitoring which shows only moment-to-moment levels, HbA1c provides a comprehensive picture of glucose control, helping healthcare providers adjust treatment plans and motivating patients by demonstrating the effectiveness of their diabetes management efforts.
• Glycemic control is best evaluated by the combination of results from SMBG and HbA1c testing, as HbA1c testing alone does not provide a measure of glycemic variability or hypoglycemia 1.

From the Research

Significance of Hemoglobin A1c (HbA1c)

• HbA1c is an important indicator of long-term glycemic control, reflecting the cumulative glycemic history of the preceding two to three months 2
• It provides a reliable measure of chronic hyperglycemia and correlates well with the risk of long-term diabetes complications 2
• Elevated HbA1c is regarded as an independent risk factor for coronary heart disease and stroke in subjects with or without diabetes 2
• HbA1c is a widely used tool for diagnosing, screening, and managing patients with diabetes, and its proper application and interpretation are crucial for accurate assessment of patients 3

Role of HbA1c in Diagnosis and Prognosis

• HbA1c is a reliable biomarker for the diagnosis and prognosis of diabetes, providing valuable information for diagnosis and treatment 2
• The American Diabetes Association recommends HbA1c as a possible substitute for fasting blood glucose for diagnosis of diabetes 2, 4
• HbA1c screening for diabetes has been found to be convenient and effective in diagnosing diabetes, particularly in community-based and acute care settings 4
• However, HbA1c testing may underestimate the prevalence of diabetes, particularly among certain racial groups, and may not be valid in certain subgroups such as children, women with gestational diabetes, and patients with human immunodeficiency virus 4, 5

Implications of Using HbA1c as a Diagnostic Marker

• The use of HbA1c as a diagnostic marker for diabetes has significant implications, including the potential to diagnose more patients and improve treatment outcomes 5
• However, the limitations of HbA1c testing, such as its potential to underestimate glycemic levels, must be clearly understood and considered in clinical judgment 5
• The cut-off value of HbA1c ≥6.5% identifies fewer diabetics than glucose-based criteria, and further guidelines are needed to clarify the appropriate use of HbA1c screening in certain populations 4, 5
• The use of HbA1c as a screening and diagnostic test is supported by its convenience, reliability, and ability to reflect longer-term glycemia, but errors caused by non-glycemic factors must be minimized 6