HbA1c test: glycated hemoglobin values and diabetes

Diabetes can progress for years without any symptoms, while high blood glucose silently damages the blood vessels, kidneys, eyes and nerves. The good news is that it can be detected with a simple blood test, long before any discomfort appears. And the key test for that — alongside blood glucose — is glycated hemoglobin (HbA1c), also known as glycosylated hemoglobin. This guide explains what it measures, how to interpret it and why it has become so important.

What is glycated hemoglobin?

Hemoglobin is the protein in red blood cells that carries oxygen. When glucose is circulating in the blood, some of it "sticks" to that hemoglobin in a stable way. The more glucose there has been over recent months, the more hemoglobin ends up "sugared". That is what glycated hemoglobin (HbA1c or A1c) measures: the percentage of hemoglobin with glucose attached to it. The older term "glycosylated" refers to the same thing.

Because red blood cells live for around 120 days, HbA1c reflects your average blood glucose over the past 2 to 3 months. It does not care what you ate yesterday or whether you came in fasting: it is a measure of how your glucose has been over a sustained period.

Blood glucose vs. glycated hemoglobin: the snapshot and the film

These are two different, complementary tests:

• Fasting blood glucose: measures the sugar in your blood at that one specific moment. It is a snapshot. That is why it is done fasting, so the last meal does not alter it.
• Glycated hemoglobin (HbA1c): measures the average over the past 2–3 months. It is the film.

Blood glucose can look fine on one particular day and yet the HbA1c can still be high if glucose was elevated on all the other days. That is why glycated hemoglobin has become the reference for diagnosis and, above all, for the monitoring of diabetes.

Reference values at Laboratorio Aclimu

These are the reference values that Laboratorio Aclimu reports for blood glucose and glycated hemoglobin in adults. They can vary slightly depending on the laboratory and the method; always compare against the reference range on your own report.

Test	Reference value (Aclimu)	Sample / method
Blood glucose	70 – 100 mg/dL	Plasma · hexokinase
Glycated hemoglobin (HbA1c)	4.8 – 5.9 %	EDTA whole blood · immunoturbidimetry

How it is interpreted for diagnosis

Beyond the laboratory's reference range, international guidelines (the ADA and the Argentine Diabetes Society) define diagnostic cut-off points. A diagnosis of diabetes is not made from a single test: it is confirmed with a second abnormal result.

Category	HbA1c	Fasting blood glucose	OGTT (2 h)
Normal	Below 5.7%	Below 100 mg/dL	Below 140 mg/dL
Prediabetes	5.7% – 6.4%	100 – 125 mg/dL	140 – 199 mg/dL
Diabetes	6.5% or higher	126 mg/dL or higher	200 mg/dL or higher

The OGTT is the oral glucose tolerance test (the "glucose curve"): fasting glucose is measured, you drink a solution with 75 g of glucose, and it is measured again 2 hours later. It is especially useful in pregnancy and in unclear cases.

What is prediabetes and why does it matter?

Prediabetes is an in-between zone: glucose is higher than normal but has not yet reached the diabetes range. It is not a minor finding. It signals a real risk of developing type 2 diabetes over the coming years, along with a higher cardiovascular risk. The big advantage is that it is the ideal moment to act: with changes in diet, weight loss and physical activity, a significant share of people with prediabetes manage to return to normal values and avoid (or delay) diabetes.^1,2

Monitoring: HbA1c in people who already have diabetes

In a person already diagnosed with diabetes, glycated hemoglobin is the main tool for knowing whether treatment is working. It is usually measured every 3 to 6 months. The general target is typically an HbA1c below 7%, but it is not the same for everyone: in older people or those with other conditions a somewhat more flexible target may be set, and the exact goal is always defined by the doctor on an individual basis.¹

When should you get tested?

Guidelines recommend assessing glucose during an adult's routine health check, and doing so more often if you have risk factors: overweight or obesity, a family history of diabetes, high blood pressure, high cholesterol or triglycerides, a sedentary lifestyle, or a history of diabetes during pregnancy. Type 2 diabetes shares ground with other check-up values — such as the lipid profile and insulin resistance — so it is often worth looking at them together.

At Laboratorio Aclimu

At Laboratorio Aclimu (Marcelo T. de Alvear 2337, Recoleta (Barrio Norte), Buenos Aires) you can have your blood glucose and glycated hemoglobin done as part of a routine check-up. Our diabetes monitoring check-up brings together the tests designed to track glucose and its impact in a single blood draw, and blood glucose is part of all our general clinical panels. You can book online, with or without a doctor's order if you want to come as a private patient, and your results arrive in your portal within a few business days.

This article was reviewed by the biochemistry team at Laboratorio Aclimu. The information is for general guidance only and does not replace a consultation with your doctor or health professional.

Frequently asked questions

What is a normal glycated hemoglobin value?

At Laboratorio Aclimu the reference value for glycated hemoglobin (HbA1c) is 4.8 to 5.9%. Guidelines consider an HbA1c below 5.7% normal, 5.7% to 6.4% prediabetes, and 6.5% or higher (confirmed) consistent with diabetes. In people who already have diabetes the usual target is below 7%, but the doctor sets it individually.

Are glycated and glycosylated hemoglobin the same?

Yes, they are the same thing. "Glycated hemoglobin" is the preferred term today and the one we use at Aclimu; "glycosylated hemoglobin" is the older name that many people still search for. Both refer to HbA1c, the same blood test.

What is the difference between blood glucose and glycated hemoglobin?

Blood glucose measures the sugar in your blood at that moment, which is why it is done fasting. Glycated hemoglobin reflects your average glucose over the past 2 to 3 months, regardless of what you ate that day. One is a snapshot; the other, a film of the last few months.

Do I need to fast for a glycated hemoglobin test?

HbA1c itself does not depend on fasting, because it measures your average over the past months. At Aclimu the preparation calls for a minimum 8-hour fast (you may drink water), mainly because it is usually ordered together with a fasting glucose and other check-up tests. We confirm the instructions when you book.

References

1. JAMA (Kalyani RR et al.). Diagnosis and Treatment of Type 2 Diabetes in Adults: A Review (2025). Available at: pubmed.ncbi.nlm.nih.gov
2. J Diabetes (Ding L et al.). Hemoglobin A1c and diagnosis of diabetes (2018). Available at: pubmed.ncbi.nlm.nih.gov
3. American Diabetes Association (Diabetes Care). 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026 (2026). Available at: pubmed.ncbi.nlm.nih.gov