From the Guidelines
Hemoglobin A1c (HbA1c) is a crucial diagnostic tool for diabetes, with a level of 6.5% or higher indicating diabetes, as recommended by the most recent guidelines 1.
Diagnosis of Diabetes
The HbA1c test measures the average blood glucose levels over the past 2-3 months by assessing the percentage of glycated hemoglobin in the blood.
- An HbA1c level of 6.5% or higher is considered diagnostic of diabetes 1.
- An HbA1c level between 5.7% and 6.4% suggests prediabetes, indicating a high risk of developing diabetes 1.
Advantages of HbA1c Testing
The HbA1c test is preferred for diagnosis because it:
- Does not require fasting 1.
- Shows long-term glucose control 1.
- Is less affected by day-to-day fluctuations compared to blood glucose tests 1.
Limitations of HbA1c Testing
However, it's essential to note that certain conditions affecting red blood cell turnover, such as:
- Anemia 1.
- Hemoglobinopathies 1. can interfere with HbA1c results. In these cases, alternative tests like fasting plasma glucose or oral glucose tolerance tests may be necessary for accurate diagnosis 1.
Clinical Practice
In clinical practice, the HbA1c test is a convenient and practical tool for diagnosing diabetes, with a high degree of standardization and accuracy 1. However, it's crucial to consider the potential limitations and interference from certain conditions, and to use alternative tests when necessary 1. The most recent guidelines recommend using an NGSP-certified method for HbA1c testing, performed in an accredited laboratory 1.
From the FDA Drug Label
The management of antidiabetic therapy should be individualized. Ideally, the response to therapy should be evaluated using HbA1c which is a better indicator of long-term glycemic control than FPG alone. HbA1c reflects glycemia over the past two to three months
HbA1c Role in Diagnosing Diabetes:
- HbA1c is used to evaluate the response to antidiabetic therapy.
- It is a better indicator of long-term glycemic control than FPG alone.
- HbA1c reflects glycemia over the past two to three months.
- No direct information is provided on the use of HbA1c in diagnosing diabetes, only in evaluating the response to therapy and monitoring glycemic control. 2
From the Research
Role of Hemoglobin (Hb) A1c in Diagnosing Diabetes
- Hemoglobin A1c (HbA1c) is used as a diagnostic criterion for diabetes, with a cut-off value of ≥6.5% 3, 4, 5, 6, 7
- HbA1c has greater stability and less variability than plasma glucose measurements, but may not always reflect glycemic levels of glycaemia 3
- The use of HbA1c as a diagnostic test has both advantages and disadvantages, and its limitations must be clearly understood to use appropriate clinical judgment and consider patient preference 3
- HbA1c screening for diabetes has been found to be convenient and effective in diagnosing diabetes, particularly in community-based and acute care settings 5
- However, HbA1c testing may underestimate the prevalence of diabetes, particularly among certain populations such as whites, children, women with gestational diabetes, patients with human immunodeficiency virus, and those with prediabetes 5, 7
Diagnostic Accuracy of HbA1c
- The sensitivity and specificity of HbA1c in diagnosing diabetes have been reported to be 73.5% and 89.1%, respectively, compared to the 2003 American Diabetes Association (ADA) criteria 7
- The kappa index of agreement between the 2003 ADA criteria and HbA1c criteria was 0.60, indicating moderate agreement 7
- The cut-off point of HbA1c for diagnosing diabetes has been reported to be 6.45%, with a sensitivity of 73.3% and specificity of 88.2% 7
- Point-of-Care (POC) HbA1c measurements have been found to have a sensitivity of 88.6% and specificity of 96.3% in diagnosing diabetes, although they may not be recommended for diagnostic purposes due to variability in results 6
Clinical Use of HbA1c
- HbA1c is widely used to assess glycemic control in people with diabetes, and is the best marker for diabetic microvascular complications 4
- HbA1c measurements can be used to report an "estimated average glucose" (eAG) in milligrams/deciliter or millimolar units, rather than as a percentage of glycated hemoglobin 4
- HbA1c has been proposed as a useful method of screening for and diagnosing diabetes, although its use as a diagnostic tool is still evolving and requires further study 4, 5