Hemoglobin A1C (HbA1c) Test: Ranges, Benefits and Limitations

If you’ve ever wondered how well your blood sugar has been controlled over the past few months, the HbA1c test gives you that answer. Unlike a standard glucose test that captures just one moment in time, HbA1c measures your average blood glucose levels over the preceding 8-12 weeks.

This blood test is one of the most valuable tools for diagnosing diabetes, monitoring treatment effectiveness, and predicting long-term health risks.

What is the Hemoglobin A1C (HbA1c) Test?

The hemoglobin A1c test measures glycated hemoglobin, which is hemoglobin with glucose molecules attached.

Hemoglobin is a protein in your red blood cells that carries oxygen throughout your body. When glucose enters your bloodstream, some of it binds to hemoglobin through a process called glycation.

As your blood sugar levels increase, more glucose attaches to your hemoglobin.

Since red blood cells live for about 120 days, the HbA1c test shows your blood sugar levels over that entire period. The test results are given as a percentage. A higher percentage means more glucose has been in your blood.

How Glycation Works

Glycation happens when glucose binds to the NH₂-terminal valine on hemoglobin’s beta chain. First, it forms an unstable structure called a Schiff base. This then undergoes something called an Amadori rearrangement to create stable HbA1c^[1].

This process is irreversible. Once glucose attaches to hemoglobin, it stays there for the life of that red blood cell.

Dr. David B. Sacks from the National Institutes of Health explains: “Formation of HbA1c is essentially irreversible, and its concentration in the blood depends on both the life span of the red blood cell, which averages ~120 days, and the blood glucose concentration.”

Your HbA1c is a weighted average. Blood sugar levels from the past 30 days contribute more to your result than levels from 90-120 days ago.

Why HbA1c Testing Matters for Long-Term Health

HbA1c doesn’t just diagnose diabetes. It also predicts your risk for serious complications such as kidney disease, vision loss, and nerve damage.  

These complications come from long-term exposure to high blood sugar. This condition harms blood vessels and speeds up cellular aging.  

A1C levels are now seen as essential for diabetes care around the world. Two important studies established this link.

The DCCT and UKPDS Studies

The Diabetes Control and Complications Trial (DCCT) followed 1,441 people with type 1 diabetes from 1983 to 1993. Participants who kept their HbA1c levels around 7% through intensive treatment had a 35-76% lower risk of microvascular complications compared to those with an HbA1c around 9%^[2].

Specific reductions included:

• 63% l (eye damage)
• 47% decrease in severe nonproliferative diabetic retinopathy
• 54% reduction in nephropathy (kidney disease) risk

The UK Prospective Diabetes Study (UKPDS) showed similar findings for type 2 diabetes. Even a modest difference in HbA1c (7.0% versus 7.9%) resulted in approximately 25% fewer microvascular complications^[3].

Both studies revealed a “legacy effect”—early intensive glucose control produced lasting benefits years later, even after HbA1c levels converged between treatment groups. This metabolic memory indicates that getting your HbA1c under control early is important for your long-term health.

HbA1c and Complications Risk

The relationship between HbA1c and complications risk is dose-dependent. Higher levels mean higher risk.

A Swedish study tracking 10,398 people with type 1 diabetes found^[4]:

• HbA1c of 7.0-7.4% showed 1.31-fold increased retinopathy risk compared to 6.5-6.9%
• HbA1c above 8.6% demonstrated 5.98-fold increased risk of proliferative retinopathy
• HbA1c above 8.6% carried 3.43-fold increased risk of macroalbuminuria (kidney damage)

Over 16-20 years of follow-up, each 1% increase in HbA1c resulted in an odds ratio of 2.87 for proliferative diabetic retinopathy and 3.83 for macroalbuminuria.

According to UKPDS analysis, each 10% relative reduction in HbA1c resulted in^[5]:

• 43% relative risk reduction for retinopathy progression
• 25% relative risk reduction for nephropathy

Understand Your HbA1c Results

The World Health Organization and major diabetes organizations have established clear thresholds for interpreting your results.

Normal, Prediabetes, and Diabetes Ranges

HbA1c Level	Classification
Below 5.7% (39 mmol/mol)	Normal
5.7% to 6.4% (39-47 mmol/mol)	Prediabetes
6.5% or higher (48 mmol/mol)	Diabetes

The WHO states: “HbA1c can be used as a diagnostic test for diabetes providing that stringent quality assurance tests are in place and assays are standardised to criteria aligned to the international reference values… An HbA1c of 6.5% is recommended as the cut point for diagnosing diabetes.”

For people already diagnosed with diabetes, treatment targets differ. The American Diabetes Association recommends an HbA1c target of less than 7% for most non-pregnant adults. The American Association of Clinical Endocrinologists suggests 6.5% if achievable safely.

For children and adolescents with type 2 diabetes, the 2025 ADA guidelines recommend an HbA1c goal of less than 6.5%.

How HbA1c Translates to Average Blood Glucose

To make HbA1c more intuitive, researchers developed estimated average glucose (eAG). This converts your percentage into the average blood sugar level you’ve maintained.

The A1c-Derived Average Glucose study included 507 people across 10 international centers. It demonstrated a tight correlation (r = 0.92) between HbA1c and average glucose^[6].

HbA1c (%)	Estimated Average Glucose
5%	97 mg/dL (5.4 mmol/L)
6%	126 mg/dL (7.0 mmol/L)
7%	154 mg/dL (8.6 mmol/L)
8%	183 mg/dL (10.2 mmol/L)
9%	212 mg/dL (11.8 mmol/L)
10%	240 mg/dL (13.4 mmol/L)

The formula is: eAG (mg/dL) = 28.7 × HbA1c − 46.7

Benefits of HbA1c Over Standard Glucose Tests

HbA1c offers several practical advantages over traditional glucose testing.

You don’t need to fast. The test can be performed any time of day, regardless of when you last ate. This eliminates the inconvenience of overnight fasting required for fasting plasma glucose tests.

Results are stable and reproducible. Blood glucose fluctuates widely throughout the day. HbA1c varies minimally (approximately 1%) in healthy individuals.

Acute factors don’t affect it. Your results aren’t thrown off by stress, exercise, or what you ate yesterday.

It reflects chronic exposure. HbA1c provides a comprehensive view of glucose control over 2-3 months, which better correlates with long-term complication risk than single glucose measurements^[7].

When HbA1c Results Can Be Misleading

Despite its utility, HbA1c has limitations that can affect accuracy.

Conditions That Affect Red Blood Cells

Any condition that changes how long your red blood cells survive will affect your HbA1c.

Conditions causing falsely low HbA1c:

• Hemolytic anemia (red blood cells break down too quickly)
• Chronic kidney disease (shortened RBC survival)
• Recent blood transfusion
• Treatment with erythropoietin

Conditions causing falsely high HbA1c:

• Iron deficiency anemia
• B12 or folate deficiency anemia
• Asplenia (absence of spleen)

Hemoglobin variants like HbS, HbE, HbD, and HbC can interfere with some HbA1c assay methods. Depending on the variant and testing method, results can be spuriously increased or decreased^[8].

Individual Variations in HbA1c

Research shows that some people have higher average HbA1c levels independent of their actual blood glucose control.

Studies consistently demonstrate that individuals who identify as Black or African American have approximately 0.3-0.5% higher HbA1c levels compared with non-Hispanic White individuals, even after adjusting for glucose measures.

Dr. Mary Rhee from the Atlanta VA Health Care System and Emory University has highlighted the clinical implications: “HbA1c mismatches are not widely appreciated, but we found that they are not uncommon, and can have important clinical implications. Because HbA1c mismatches could lead to errors, the diagnoses of diabetes/prediabetes should include measurement of fasting glucose levels and/or oral glucose tolerance tests in addition to HbA1c in most Veterans.”

A UK study found that children and young people from Black ethnic backgrounds demonstrated approximately 4-5 mmol/mol higher HbA1c than their White and South Asian counterparts, independent of mean blood glucose levels^[9].

This is why your test result should be interpreted within the context of individual patient factors and combined with other assessments.

How Often Should You Test HbA1c?

Diabetes Canada and other organizations provide clear guidance on testing frequency.

• For patients not meeting glucose targets or with recent therapy changes: every 3 months
• For patients with stable, well-controlled diabetes: every 6 months

HbA1c should not be measured more than 4 times yearly in most circumstances. Since the test reflects 2-3 months of glucose exposure, testing more frequently doesn’t provide new information.

Test Your HbA1c with AgingSOS

Jinfiniti’s AgingSOS includes HbA1c testing as part of a comprehensive longevity assessment.

You’ll get HbA1c measured alongside 27 other biomarkers including intracellular NAD+, Klotho (the longevity protein), inflammation markers, oxidative stress indicators, and cardiovascular risk factors.

This complete picture helps you detect metabolic issues years before symptoms appear. You can track how your interventions—whether supplements, diet changes, or exercise—affect your HbA1c and other aging markers over time.

The AgingSOS Longevity Panel includes a free consultation to help you interpret your results and develop a personalized optimization strategy.

Mobile phlebotomy is available for convenient at-home blood collection.