The HbA1c test — a simple blood test that needs no fasting. It measures the percentage of haemoglobin carrying glucose, revealing your average blood sugar control over the past 2–3 months. It is the cornerstone of diabetes monitoring and is widely used for diagnosis in Sri Lanka.
Written & Reviewed by
MBBS (Col) · MD (Col) · SLMC No. 27329 · Medical Director, Sineth Hospitals
🩺 Medically Reviewed
📅 Updated: April 2026
🕐 7 min read
🔬 Overview
What is the HbA1c Test?
The HbA1c test (Glycated Haemoglobin test) measures the percentage of haemoglobin in your red blood cells that has glucose attached to it. When glucose circulates in your blood, a portion of it naturally binds to haemoglobin — the protein that carries oxygen inside red blood cells. The higher your blood sugar has been over time, the more haemoglobin becomes glycated.
Because red blood cells live for approximately 2–3 months, the HbA1c result reflects your average blood sugar level over that entire period — not just at a single moment in time. This makes it far more informative than a random or fasting blood glucose test for understanding long-term sugar control.
Simple blood test — no fasting required
Reflects 2–3 month average blood sugar
Can be done at any time of day
Result expressed as a percentage (%)
Why HbA1c is different from other blood sugar testsA fasting blood sugar (FBS) or postprandial blood sugar (PPBS) captures your glucose level at one specific moment, which can fluctuate day to day. The HbA1c test is not affected by what you ate yesterday or whether you are stressed today. It gives a stable, long-term picture of how well your blood sugar has been controlled — making it the preferred test for monitoring diabetes and screening at-risk individuals.
⭐ Why It Matters
Why is HbA1c Important?
HbA1c is one of the most widely used tests in diabetes care. It serves two major roles: diagnosing diabetes and prediabetes, and monitoring long-term blood sugar control in people already living with diabetes.
Key Advantages Over Other Tests
No fasting required — come at any time
Reflects long-term control, not daily fluctuations
Reproducible — less affected by acute illness than fasting glucose
Directly linked to risk of complications
HbA1c and the risk of complicationsChronically elevated blood sugar — reflected by a high HbA1c — is the underlying cause of the long-term complications of diabetes: damage to the eyes (diabetic retinopathy), kidneys (diabetic nephropathy), and nerves (diabetic neuropathy). Keeping your HbA1c within the target range significantly reduces the risk of developing these complications. This is why HbA1c monitoring is such a central part of diabetes management.
📋 When It Is Recommended
When Should You Do an HbA1c Test?
For Diagnosis — Who Should Be Tested?
HbA1c is especially useful for screening and diagnosing diabetes and prediabetes in the following groups:
- 1Overweight or obese individuals — particularly if BMI is 25 or above (or lower cut-offs in South Asians)
- 2Strong family history of diabetes — especially first-degree relatives (parents, siblings) diagnosed before age 50, or multiple affected family members
- 3Hypertension (high blood pressure) or other features of metabolic syndrome
- 4Routine screening in adults aged 35–40 and above in Sri Lanka, where Type 2 diabetes is increasingly prevalent at younger ages
What Counts as a "Strong" Family History?
Not all relatives with diabetes convey the same level of inherited risk. The following situations are considered more significant:
Parent or sibling with diabetes
Relative diagnosed before age 50
Multiple affected family members across generations
Relative with early-onset diabetes associated with obesity
A single elderly relative matters lessA grandparent or distant relative diagnosed with diabetes late in life (after age 60 or 65) carries a lower level of inherited risk compared to a parent or sibling diagnosed early, especially if multiple family members are affected. If your only family history is one elderly relative diagnosed late, your risk is lower — though not zero.
For Monitoring — Patients Already Diagnosed with Diabetes
Every 3 months if blood sugar is uncontrolled or treatment has changed
Every 6 months if blood sugar is stable and well controlled
To assess how well current medications are working
To evaluate risk of long-term complications
🧪 How the Test Works
How is the HbA1c Test Done?
The HbA1c test is one of the most straightforward blood tests available. There is no preparation required beyond arriving at the laboratory.
- 1A small blood sample is taken — usually from a vein in your arm, exactly like any other routine blood test.
- 2No fasting needed — you can eat, drink, and take your medications as normal before the test.
- 3No glucose drink required — unlike the OGTT, there is nothing to drink and no waiting period in the laboratory.
- 4Result is returned as a percentage — for example, 7.2%, which your doctor interprets against standard reference ranges.
No special preparation — but inform the lab about these conditionsWhile HbA1c requires no fasting or dietary changes, you should always inform the laboratory if you have: recent significant bleeding or blood loss, a recent blood transfusion, known anaemia (especially iron-deficiency anaemia), or a known haemoglobin disorder (such as sickle cell trait or thalassaemia). These conditions can affect the accuracy of the result.
📊 Reference Values & Targets
HbA1c Reference Values & Interpretation
The table below shows the standard diagnostic thresholds used internationally and in Sri Lanka.
| Category | HbA1c (%) | Interpretation |
|---|---|---|
| Normal | < 5.7% | Normal |
| Prediabetes | 5.7% – 6.4% | At Risk — Prediabetes |
| Diabetes | ≥ 6.5% | Diabetes |
Prediabetes is an important warningAn HbA1c in the prediabetes range (5.7%–6.4%) does not mean you have diabetes — but it is a strong signal that your blood sugar regulation is impaired. Without lifestyle changes, many people with prediabetes progress to Type 2 diabetes within 5–10 years. Prediabetes can often be reversed with weight loss, regular physical activity, and dietary changes.
Treatment Targets for Patients Already Diagnosed with Diabetes
Once diabetes is diagnosed, the HbA1c target depends on the individual. Your doctor will set a personalised target based on your age, other health conditions, and the risk of hypoglycaemia. General guidelines are:
| Control Level | HbA1c Target | Status |
|---|---|---|
| Good control | < 7% | Well Controlled |
| Moderate control | 7% – 8% | Needs Attention |
| Poor control | > 8% | Review Treatment |
Targets may be adjusted for individual circumstancesA stricter target (e.g. below 6.5%) may be appropriate for younger patients with no complications who are at low risk of hypoglycaemia. A more relaxed target (e.g. below 8%) may be appropriate for elderly patients, those with severe hypoglycaemia episodes, or those with limited life expectancy. Pregnancy also requires specific targets. Always follow the personalised advice of your doctor.
What Do Abnormal Results Mean?
High HbA1c — poor long-term blood sugar control; increased risk of complications
Very high (>9%) — significantly elevated complication risk; treatment review urgently needed
Low HbA1c in a treated diabetic — may indicate frequent low blood sugar (hypoglycaemia) episodes
Borderline (6.0%–6.4%) — prediabetes range; lifestyle intervention indicated
⚠️ Important Limitations
When HbA1c May Be Unreliable
HbA1c is a very useful test, but it is not perfect. Because it depends on haemoglobin inside red blood cells, any condition that changes red blood cell lifespan or haemoglobin structure can produce a misleading result.
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Anaemia (especially iron-deficiency anaemia) — iron deficiency causes red blood cells to live longer, increasing glucose exposure time and falsely raising the HbA1c result.
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Recent blood transfusion — transfused red blood cells have not been exposed to your blood sugar levels, falsely lowering the result.
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Chronic kidney disease (CKD) — kidney disease causes anaemia and shortens red blood cell survival, affecting the result.
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Haemoglobin disorders — sickle cell disease, thalassaemia, and other haemoglobin variants affect how the test measures glycation, potentially producing an inaccurate reading.
In these situations, use a different testIf any of the above conditions are present, the HbA1c result may not be reliable. Your doctor may prefer a fasting blood glucose test or an OGTT to diagnose or monitor diabetes accurately. Always inform your doctor and the laboratory if you have anaemia, kidney disease, or a known haemoglobin disorder.
🔄 Comparison
HbA1c vs OGTT — Which Test is Better?
HbA1c and the OGTT each have distinct strengths. They are not interchangeable in every situation — the right test depends on your clinical circumstances.
| Feature | HbA1c | OGTT |
|---|---|---|
| Fasting required | No | Yes (8–12 hours) |
| Time taken | A few minutes | 2–3 hours |
| Detects early (borderline) diabetes | Less sensitive | More sensitive |
| Preferred in pregnancy | Not recommended | Gold standard (GDM) |
| Reliable with anaemia or haemoglobin disorders | No | Yes |
| Reflects long-term control | Yes (2–3 months) | No (single time point) |
| Widely used in Sri Lanka for monitoring | Yes | No (mainly diagnostic) |
In Sri Lanka
• HbA1c → widely used for routine screening, diagnosis in stable patients, and ongoing monitoring
• OGTT → essential in pregnancy for diagnosing gestational diabetes (GDM); also preferred when HbA1c may be unreliable
The two tests are often complementary — a borderline HbA1c result may warrant an OGTT for confirmation, particularly in younger patients or when early diabetes needs to be excluded with higher confidence.
• HbA1c → widely used for routine screening, diagnosis in stable patients, and ongoing monitoring
• OGTT → essential in pregnancy for diagnosing gestational diabetes (GDM); also preferred when HbA1c may be unreliable
The two tests are often complementary — a borderline HbA1c result may warrant an OGTT for confirmation, particularly in younger patients or when early diabetes needs to be excluded with higher confidence.
❌ Common Mistakes
Common Mistakes — and How to Avoid Them
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Ignoring known anaemia — if you have iron-deficiency anaemia or any blood disorder, tell your doctor before relying on HbA1c results. A falsely elevated HbA1c in an anaemic patient can lead to unnecessary treatment.
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Testing during acute illness — acute illness or recent surgery can temporarily affect blood sugar levels. HbA1c is less affected than random glucose, but testing during an acute event is still not ideal for making long-term management decisions.
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Assuming one normal result is enough forever — HbA1c should be repeated at intervals appropriate to your risk. A normal HbA1c today does not provide lifelong reassurance — especially if you have ongoing risk factors such as obesity or a strong family history.
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Misinterpreting "borderline" values — an HbA1c of 6.0% or 6.1% is not diabetes, but it is prediabetes and requires action. Dismissing a borderline result as "almost normal" misses the opportunity for preventive intervention.
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Stopping medications before the test — some patients stop their diabetes medications hoping to "reset" their result. This does not help — HbA1c reflects the last 2–3 months, so omitting medication for a few days before the test makes no meaningful difference to the result but can be harmful to your blood sugar control.
❓ Frequently Asked Questions
Frequently Asked Questions
No. The HbA1c test does not require any fasting. You can eat and drink normally before the test. This is one of its key practical advantages over fasting blood glucose tests.
Yes — the HbA1c test can be done at any time of day, morning or afternoon. Because no fasting is required and the result reflects a 2–3 month average, the timing of the day makes no difference to the result.
Usually yes. A single HbA1c of 6.5% or above — confirmed on a repeat test if the patient has no symptoms — is generally sufficient to diagnose diabetes. However, in borderline cases, or when an underlying condition may affect the result, your doctor may request a fasting blood glucose or OGTT for confirmation.
HbA1c is not recommended for diagnosing gestational diabetes. The OGTT (Oral Glucose Tolerance Test) is the gold standard for gestational diabetes screening in pregnancy in Sri Lanka. HbA1c may be used in very early pregnancy to screen for pre-existing undiagnosed Type 2 diabetes, but not for routine gestational diabetes testing.
- Every 3 months — if your diabetes is poorly controlled or you have recently changed your treatment
- Every 6 months — if your blood sugar is stable and well controlled
Yes — HbA1c can be inaccurate in conditions affecting red blood cells. Specifically: iron-deficiency anaemia (can falsely raise the result), recent blood transfusion (can falsely lower it), chronic kidney disease, and haemoglobin disorders such as sickle cell disease or thalassaemia. In these situations, fasting blood glucose or OGTT is more reliable.
No. Continue all your medications as prescribed — including your diabetes medications. Stopping medication for a few days before the test makes no meaningful difference to the HbA1c result, because it reflects the average of the last 2–3 months. Stopping medication unnecessarily can be harmful to your blood sugar control.
🎯 Key Takeaways
- HbA1c measures your average blood sugar over the past 2–3 months — not just at one moment in time
- No fasting required — it can be done at any time of day
- Normal: below 5.7% | Prediabetes: 5.7%–6.4% | Diabetes: 6.5% or above
- Treatment target for most diabetic patients: below 7% — personalised by your doctor
- Not recommended for diagnosing gestational diabetes in pregnancy — OGTT is preferred
- May be unreliable in anaemia, recent blood transfusion, kidney disease, or haemoglobin disorders
- For ongoing diabetes management, always interpret HbA1c alongside your doctor's clinical assessment