A1C vs HbA1c: What is the Difference?

If you’ve looked at a lab report from your US doctor and then compared it to one from a clinic in the UK or Canada, you may have noticed something odd. One says “A1C.” The other says “HbA1c.” Same blood test, same result, completely different label — and nobody in the room explains why.

This discrepancy confuses patients constantly, and understandably so. When you’re managing a chronic condition and two reports use two different terms for what appears to be the same number, it’s natural to wonder if something is being measured differently. It isn’t. But the story of how two names ended up for one test is actually worth knowing — because it affects how you read international lab results and why the numbers don’t always look identical across borders.

The Short Answer

A1C and HbA1c are exactly the same test measuring exactly the same thing. “HbA1c” is the full scientific name used in labs, journals, and most countries outside the US. “A1C” is the simplified version the American Diabetes Association standardized for US clinical and patient use. If your result is 7.0% in New York, it would also be 7.0% if labeled HbA1c in London — assuming both labs are using NGSP-certified methods.

Where Each Name Comes From

The full scientific name has always been HbA1c. Breaking it down: “Hb” is the chemical symbol for hemoglobin, the iron-rich protein inside red blood cells. “A” refers to adult hemoglobin — the dominant form in healthy adults, making up roughly 95–98% of total hemoglobin. The “1” identifies a chromatographic fraction that bonds with carbohydrate molecules, and the lowercase “c” pinpoints the specific sub-fraction where glucose — and only glucose — attaches.

That specificity is why this particular fraction became the diagnostic standard in the first place. The A1a and A1b fractions bond with other sugar-related compounds like fructose and pyruvic acid. Only A1c bonds exclusively with glucose — which is what makes it an accurate window into long-term blood sugar control. If you want to understand the full chemistry behind that bond, our article on what A1C actually stands for breaks it down step by step.

The simplified “A1C” name is an American invention. In the late 1990s, the ADA was working to make diabetes education more accessible. The term “HbA1c” was considered intimidating — hard to pronounce, hard to remember, and unfamiliar-looking to patients who weren’t scientists. So the ADA officially dropped the “Hb” in all its patient-facing materials and standardized the term to “A1C.” US clinics, insurance companies, and pharmacy chains followed, and the shorter version became the norm in American healthcare.

HbA1c

Full scientific name
Standard in UK, Europe, Canada, Australia
Used in medical journals worldwide
Often paired with mmol/mol (IFCC)
More common in formal lab reports internationally

A1C

Simplified patient-facing name
Standard in the United States
Adopted by ADA in the late 1990s
Always reported as a percentage (NGSP)
Used in US clinics, insurance, consumer tools

The Units Problem — Why the Numbers Sometimes Don’t Match

Here’s where it gets slightly more complicated. Even though A1C and HbA1c measure the same thing, labs in different countries don’t always express the result in the same units. And that’s where patients get genuinely confused — not because the tests are different, but because the reporting systems are.

The United States uses the NGSP (National Glycohemoglobin Standardization Program) format, which reports results as a percentage. When your doctor says your A1C is 7.2%, that percentage is an NGSP figure.

Most of Europe, the UK, and international research institutions use the IFCC (International Federation of Clinical Chemistry) format, which reports in millimoles of glycated hemoglobin per mole of total hemoglobin — written as mmol/mol. An A1C of 7.0% in NGSP terms equals 53 mmol/mol in IFCC terms. The same patient, the same blood, just expressed differently.

A1C — NGSP (%)	HbA1c — IFCC (mmol/mol)	Est. Average Glucose (mg/dL)	Clinical Zone
5.7%	39 mmol/mol	117 mg/dL	Prediabetes threshold
6.0%	42 mmol/mol	126 mg/dL	High-risk prediabetes
6.5%	48 mmol/mol	140 mg/dL	Diabetes diagnosis cutoff
7.0%	53 mmol/mol	154 mg/dL	Standard treatment target
8.0%	64 mmol/mol	183 mg/dL	Sub-optimal control
9.0%	75 mmol/mol	212 mg/dL	High vascular risk

The conversion between the two isn’t complicated, but it’s easy to misread a result if you’re not expecting the format difference. If you receive an HbA1c report from an international clinic showing a number like 53, don’t panic — that’s equivalent to 7.0% in US terms, which is a standard management target.

Why the IFCC number is always lower than the NGSP percentage: The IFCC method uses a more chemically precise reference standard — it excludes certain labile fractions that older methods counted. This produces a lower absolute number. Neither is “wrong”; they just measure with different precision. The 2007 international consensus agreement confirmed both systems are valid and encouraged labs to report both on the same result sheet.

How the Two Standards Came to Coexist — A Brief History

1968: Dr. Samuel Rahbar identifies HbA1c

Working in Tehran, Rahbar notices elevated levels of an unusual hemoglobin component in diabetic patients — the compound that would become the basis of the A1C test.

1993: DCCT trial proves A1C’s clinical value

The Diabetes Control and Complications Trial demonstrates definitively that lowering HbA1c reduces microvascular complications. This makes standardized measurement urgent — results from different labs couldn’t be reliably compared.

1996: NGSP launches in the US

The National Glycohemoglobin Standardization Program anchors US lab results to DCCT data. All certified US labs now produce comparable percentage results.

Late 1990s: ADA simplifies “HbA1c” to “A1C”

The American Diabetes Association drops the “Hb” in patient materials to reduce intimidation and improve health literacy. US clinical practice follows.

2007: ADA, EASD, and IDF reach global consensus

International diabetes organizations agree that both NGSP (%) and IFCC (mmol/mol) are valid reporting formats. Labs worldwide are encouraged to report both side by side on patient results.

Does the Name on Your Lab Report Affect Anything Practical?

No — not for your treatment. Whether your report says A1C or HbA1c, your doctor is looking at the same number and applying the same clinical thresholds. The diabetes diagnosis cutoff is 6.5% regardless of which label appears on the page. The standard treatment target of below 7.0% applies equally to both.

Where it does matter is insurance and billing. In the United States, both A1C and HbA1c tests are billed under the same CPT code: 83036. Medicare, Medicaid, and private insurers recognize both terms as the same test. You won’t be billed differently, and you won’t have a claim denied because one term was used instead of the other.

It also matters when comparing results across different time periods or different healthcare systems. If you were tested in the UK last year and have a result in mmol/mol, and you’re now being managed in the US with percentage results, your doctor needs to convert between the two before comparing trends. The numbers aren’t directly comparable on their face — 53 and 7.0% look completely different but mean exactly the same thing.

At-Home Tests: Does the Name Affect Accuracy?

At-home A1C kits sold in the US are calibrated to NGSP standards and report a percentage — the same format as your US lab report. They don’t use the HbA1c label, but they’re measuring the same fraction of glycated hemoglobin. The accuracy question isn’t really about the name — it’s about whether the kit is NGSP-certified and whether a small point-of-care device can match the precision of a hospital HPLC machine.

The honest answer is: close, but not identical. Most certified home kits perform well enough for trend tracking between lab visits. They’re more vulnerable to interference from hemoglobin variants and extreme sample conditions than large lab systems. Our article on at-home A1C test accuracy walks through what the research shows about how closely home kits match lab results — and when the gap matters enough to rely on the lab instead.

One More Term You Might See: Glycosylated Hemoglobin

Older lab reports and some medical literature use a third term — “glycosylated hemoglobin” — as a synonym for HbA1c. Clinically, it means the same thing. Technically, there’s a slight distinction: glycosylation refers to enzyme-driven sugar attachment, while glycation is the spontaneous non-enzymatic process that actually produces HbA1c. The glucose bonding to hemoglobin in the A1C test is glycation, not glycosylation. But in everyday clinical language, you’ll see both terms used interchangeably, and either one on a lab report refers to the same test.

What To Take Away From This

A1C and HbA1c are the same test. The name difference is geographic and stylistic, not medical.
“HbA1c” is the scientific name used internationally; “A1C” is the ADA-simplified version used in the United States.
The unit difference matters more than the name: US labs report a percentage (NGSP); international labs may report mmol/mol (IFCC). An A1C of 7.0% equals 53 mmol/mol.
Both formats are clinically valid. A 2007 global consensus confirmed labs should ideally report both on the same result sheet.
Insurance billing uses the same CPT code (83036) for both. The name on the report doesn’t affect coverage.
If your result comes from a different country and looks unfamiliar, check whether it’s in mmol/mol before assuming anything is wrong.

Got a Result in mmol/mol?

If your HbA1c result is in IFCC units from a UK or international clinic, use our A1C to mmol/mol converter to translate it into the US percentage format — or the other way around.

Frequently Asked Questions

If I get tested in the US and then again in Canada, will my results look the same?

The underlying measurement will be the same, but Canadian lab reports may express HbA1c in mmol/mol (IFCC format) rather than as a percentage. So an A1C of 7.0% from your US lab would appear as 53 mmol/mol on a Canadian or UK report. Same result, different unit — just convert between them if you’re comparing.

My lab report shows both a percentage and a mmol/mol number. Which one should I focus on?

If you’re in the US and being treated by a US physician, focus on the percentage — that’s what your doctor’s clinical targets are based on. If you’re in Europe or the UK, the mmol/mol figure is primary. Some modern labs report both as a convenience, especially for patients who travel or compare results internationally.

Is “glycated hemoglobin” the same as HbA1c?

Yes, used synonymously in clinical practice. The full form “glycated hemoglobin” appears in older literature and some formal lab reports. It describes the same biological process — glucose bonded to hemoglobin — that produces the A1C/HbA1c result.

Does fetal hemoglobin (HbF) interfere with the A1C test?

It can, in some adults. Fetal hemoglobin doesn’t have the same beta chains as adult hemoglobin, so it doesn’t glycate in the same way. Adults who retain elevated HbF levels — a condition called hereditary persistence of fetal hemoglobin — may get a falsely low A1C result on standard chromatographic tests. Labs using HPLC will typically flag this on the chromatogram.

Why does my A1C test result sometimes differ from what my CGM suggests?

The A1C and a CGM’s Glucose Management Indicator (GMI) are measuring related but different things. A1C reflects actual glycated hemoglobin in your blood. GMI is an estimate derived from your average sensor glucose readings. The two can diverge by 0.3–0.5 percentage points, especially if you have anemia or certain hemoglobin variants. For a deeper look at why the two don’t always line up, our article on A1C versus CGM data covers the key differences and when each is more reliable.

Is the HbA1c test used to diagnose diabetes in all countries?

In most, yes — but not all. The US and many other countries accept an HbA1c of 6.5% or above (on two occasions) as diagnostic for type 2 diabetes. Some countries still prefer fasting glucose or oral glucose tolerance tests for diagnosis, particularly because HbA1c can be unreliable in populations with high rates of hemoglobin variants. The comparison between A1C and fasting blood sugar as diagnostic tools explains the practical trade-offs between these approaches.

What’s the difference between HbA1c and fructosamine — and when is fructosamine used instead?

HbA1c measures glucose bonded to hemoglobin inside red blood cells, reflecting roughly 90 days of blood sugar history. Fructosamine measures glucose bonded to serum proteins (mainly albumin) in the liquid portion of your blood. Because albumin has a much shorter lifespan — around two to three weeks — fructosamine gives a shorter-term average. Doctors typically use it when A1C is unreliable, such as in patients with hemolytic anemia, iron deficiency, or hemoglobin variants where the standard test can’t be trusted.

References

A1C Diabetes Education