Hemoglobin A1c

Also known as A1c, HbA1c, glycated hemoglobin, glycohemoglobin, average blood sugar

modified protein · no single molecular formula

LOINC 4548-4 code verified whole_blood %

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

A measure of your average blood sugar over the past two to three months. Sugar sticks to red blood cells slowly, and this counts how much has stuck.

Fraction of haemoglobin non-enzymatically glycated in proportion to ambient glucose, integrating exposure over the erythrocyte lifespan.

why measured unverified

Unlike a glucose test, it cannot be gamed by one careful day. It shows the general trend rather than a single moment.

No clinical version written yet.

if high unverified

Average blood sugar has been running high. Because it covers months, a raised result is much harder to explain away than a single glucose reading.

No clinical version written yet.

caveats unverified

It assumes red blood cells live a normal length of time. If yours are being replaced faster than usual, from anaemia or recent blood loss, the result reads falsely low and cannot be trusted.

No clinical version written yet.

What this substance is

Haemoglobin with glucose irreversibly attached to the N-terminal valine of the beta chain. Reported as a percentage of total haemoglobin, so the analyte is a modification fraction rather than a compound.

UniProt P68871

Each molecule is drawn from ChEBI's curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Atom diagrams are checked against the NIST Atomic Spectra Database.

3D model

Haemoglobin (PDB 2HHB). In HbA1c, glucose is attached to the start of each beta chain; this structure shows the unmodified protein. Experimental structure from the Protein Data Bank, entry 2HHB, shown as its biological assembly (4 chains). Every chain was checked against its UniProt sequence (at least 100.0% identical). Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

all

5.7

normal range · %

Applies to	Normal	Optimal	Critical
all	≤ 5.7 %	—	—

guideline limit A1C Test, NIDDK (National Institutes of Health) cited · not yet checked by a person

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm. You don't need to fast. Some medicines and pregnancy can affect the result, so tell your provider. Some clinics can also run the test on an approved quick-test device.

Single venous blood sample; no fasting needed. For diagnosis, use an NGSP- certified method standardized to the DCCT assay; point-of-care A1C for screening/diagnosis should be limited to FDA-approved devices in laboratories proficient in moderate-complexity testing. In conditions that alter the A1C-glycemia relationship (e.g. hemoglobinopathies including sickle cell disease, pregnancy, hemodialysis, recent blood loss or transfusion, erythropoietin therapy) only plasma glucose criteria should be used for diagnosis.

Before the test

No fasting is needed.
Tell your provider about all medicines (e.g. opioids, some HIV medicines) and if you are pregnant; don't stop any unless told to.

Where: laboratory, clinic or point of care

Sources: 2. Classification and Diagnosis of Diabetes: Standards of Care in Diabetes-2023, American Diabetes Association, Diabetes Care (PMC open access); Hemoglobin A1C (HbA1c) Test, MedlinePlus (U.S. National Library of Medicine) cited · not yet checked by a person

In the lab

chromatography

Ion-exchange HPLC

The different forms of haemoglobin, including the form with sugar attached, carry slightly different electrical charges. That lets the lab separate the sugared portion from the rest and measure what fraction it makes up.

Haemoglobin fractions, including glycated HbA1c, differ in ionic charge and separate on a cation-exchange column; HbA1c is reported as its peak area relative to total haemoglobin.

Reference method: IFCC reference methods (mass spectrometry or capillary electrophoresis)
Standardised to: NGSP certified, IFCC-traceable

What can throw it off

Haemoglobin variants (HbS, HbC, HbE) add extra peaks to the chromatogram; the result may then not be reportable and another method is needed.
Anything shortening red cell lifespan, such as haemolytic anaemia, reads falsely low.

Why labs disagree: Reported in both NGSP percent and IFCC mmol/mol, and the two numbers are not interchangeable -- 6.5% is 48 mmol/mol. Beyond units, the result assumes red cells live a normal length of time (about 120 days), so it is unreliable in anyone whose cells turn over faster.

Sources: IFCC Standardization of HbA1c: Overview, National Glycohemoglobin Standardization Program (NGSP); Laboratory Procedure Manual, Glycohemoglobin (Tosoh G8), NHANES 2017-2018, CDC/NCHS cited · not yet checked by a person

What it reports on

erythrocyte structural component of
HbA1c is glucose stuck to hemoglobin inside red blood cells, and it lasts as long as those cells live.
islet of Langerhans regulated by
Beta cells in the islets make insulin, which helps control blood glucose, and HbA1c reflects average blood glucose.
pancreas regulated by
The pancreas makes insulin, which moves glucose out of the blood, so it shapes the average glucose that HbA1c shows.

Associated symptoms

When high

high Urinating much more than usual · suggestive · occasional
high Feeling tired all the time · non specific · common
high Pins and needles, or numbness · suggestive · occasional
Sustained high glucose damages small peripheral nerves over years.

Conditions this marker features in

When high

high Blood sugar higher than normal, but not diabetes · defining
ADA criterion: an A1C of 5.7–6.4%, the band between normal and diabetes.
high Fatty liver · defining
One of the five cardiometabolic criteria (any one is enough, with fat in the liver): HbA1c 5.7% or higher, fasting glucose 100 mg/dL or higher, or type 2 diabetes or its treatment.
high Type 2 diabetes · defining
HbA1c 6.5% (48 mmol/mol) or higher, measured with a certified lab method.
high A cluster of risks that travel together · supportive
Often raised, but not part of the standard criteria, which use fasting glucose. Using HbA1c instead identifies a partly different group of people.

Ordered as part of

metabolic_risk