HbA1c Explained: What Your Blood Sugar Number Really Means

If you have been diagnosed with Type 2 diabetes or prediabetes, you have almost certainly seen the term HbA1c on your blood test results. It is the most important single number in diabetes management — more informative than fasting glucose, more predictive of complications, and the primary target of every treatment decision. Yet many patients leave the clinic not fully understanding what it measures, what their target should be, or how to move it in the right direction.

What Does HbA1c Actually Measure?

HbA1c stands for glycated haemoglobin. Haemoglobin is the protein inside red blood cells that carries oxygen. When glucose circulates in the blood, it attaches irreversibly to haemoglobin molecules through a non-enzymatic process called glycation. The higher your blood glucose over time, the greater the proportion of haemoglobin that becomes glycated.

Because red blood cells have a lifespan of approximately 90–120 days, HbA1c reflects the average blood glucose concentration over the preceding 2–3 months.^[1] This is what makes it so clinically valuable: it cannot be manipulated by a single day of dietary restriction before a test, as a fasting glucose can be.

HbA1c is reported either as a percentage (the NGSP/DCCT standard used in the USA and many other countries) or in mmol/mol (the IFCC standard used increasingly in the UK and Europe). A value of 6.5% is equivalent to 48 mmol/mol.

The Diagnostic and Target Thresholds

The World Health Organization and the American Diabetes Association define the HbA1c thresholds as follows:^[2,3]

• Below 5.7% (39 mmol/mol): Normal
• 5.7–6.4% (39–47 mmol/mol): Prediabetes (impaired glucose regulation)
• 6.5% (48 mmol/mol) or above: Diagnostic of Type 2 diabetes on two separate occasions
• Below 6.5% for 3+ months without medication: Remission of Type 2 diabetes^[4]

For patients already diagnosed with Type 2 diabetes, the general treatment target is HbA1c below 7.0% (53 mmol/mol), though this is individualised based on age, cardiovascular risk, hypoglycaemia risk, and the patient’s own goals.^[2] Tighter targets of below 6.5% are appropriate for younger patients, those recently diagnosed, and those with low hypoglycaemia risk.

Why Fasting Glucose Alone Is Insufficient

Many patients ask: “My fasting glucose was normal — so why is my HbA1c elevated?” The answer lies in postprandial glucose excursions — the spikes in blood sugar that occur after meals. Fasting glucose measures only the overnight baseline. It can appear entirely normal while post-meal glucose regularly spikes above 10–12 mmol/L (180–216 mg/dL), causing significant HbA1c elevation and driving microvascular complications.

Continuous Glucose Monitor (CGM) studies have demonstrated that in patients with normal fasting glucose but prediabetes-range HbA1c, post-meal glucose patterns are the primary driver of glycated haemoglobin.^[5] This is why we use fasting glucose, HbA1c, and fasting insulin together in a complete metabolic assessment — not any single marker in isolation.

HbA1c and Complication Risk: The Numbers That Matter

The landmark UK Prospective Diabetes Study (UKPDS) established the relationship between HbA1c and diabetic complication rates with precision. The key findings:^[6]

• Each 1% reduction in HbA1c is associated with a 37% reduction in microvascular complications (retinopathy, nephropathy, neuropathy).
• Each 1% reduction is associated with a 14% reduction in myocardial infarction.
• There is no lower threshold of benefit — lower is better, within safe limits.

This dose-response relationship is why we do not accept an HbA1c of 8% as “acceptable” in our patients. Every percentage point above target carries a quantifiable increase in complication risk.

Limitations of HbA1c: When It Can Mislead

HbA1c is reliable in most clinical situations, but several conditions can cause falsely low or falsely high readings:^[7]

• Falsely low: Haemolytic anaemia (shorter RBC lifespan), iron deficiency anaemia treatment (new RBCs dilute glycated cells), haemoglobinopathies (HbS, HbC), chronic blood loss.
• Falsely high: Iron deficiency anaemia (before treatment), vitamin B12/folate deficiency, splenectomy (longer RBC lifespan), chronic alcohol use.

In patients with these conditions, fructosamine (a 2–3 week average of glucose) or CGM-derived glucose management indicator (GMI) are preferred alternatives.

How to Reduce Your HbA1c: The Evidence-Based Hierarchy

The most effective interventions for HbA1c reduction, ranked by average HbA1c reduction achieved in clinical trials:^[8]

1. Significant weight loss (15%+ body weight): 2.0–3.0% reduction. The most powerful single intervention.^[9]
2. Low-carbohydrate diet (<130g carbs/day): 0.9–1.5% reduction at 6 months.^[10]
3. Time-restricted eating (16:8): 0.4–0.8% reduction, comparable to metformin in some trials.^[11]
4. Structured exercise (150 min/week aerobic + resistance): 0.5–0.7% reduction.^[12]
5. Metformin: 1.0–1.5% reduction on average.^[2]
6. SGLT2 inhibitors: 0.7–1.0% reduction, with additional cardiovascular and renal benefits.^[13]

Dr. Ahmed’s Approach: 8-Week Monitoring Intervals

At SehaTalks, we measure HbA1c at baseline and every 8 weeks during the active phase of our metabolic programme. This 8-week interval — rather than the standard 3-month interval — allows earlier detection of response, faster medication adjustment, and stronger patient motivation through visible progress. Most patients in our programme see their first HbA1c improvement within the first 8-week cycle.

Key Takeaways

• HbA1c reflects your average blood glucose over the past 2–3 months.
• Diagnosis threshold is 6.5% (48 mmol/mol); treatment target for most patients is below 7.0%.
• Fasting glucose alone misses post-meal spikes that drive HbA1c elevation.
• Each 1% HbA1c reduction reduces microvascular complication risk by 37%.
• Weight loss, low-carbohydrate diet, and time-restricted eating are the most powerful non-pharmacological interventions.