Hemoglobin A1c

Also written HbA1c

MetabolicMeasured in %

What it measures

The proportion of hemoglobin that has been non-enzymatically glycated, reflecting average glucose exposure over roughly the preceding three months.

Why it matters

It is the standard measure for diagnosing and monitoring diabetes, and it requires no fasting.

Where the claimed ranges actually sit

Measured in %. Each row is one claim about where your result should fall.

What a laboratory reportsWhat a seller markets as “optimal”

Laboratory reference range< 5.7 %

Established diagnostic thresholds in wide clinical use

Under 5.3%C< 5.3 %

Longevity platforms and continuous glucose monitor programs

›View as table

Claim	Range	Source
Laboratory reference range	< 5.7 %	Established diagnostic thresholds in wide clinical use
Under 5.3%	< 5.3 %	Longevity platforms and continuous glucose monitor programs

Where the sources disagree

The diagnostic thresholds are solid. The 'optimal' targets below them are considerably shakier, because red blood cell turnover confounds the measurement precisely in the range where consumer platforms make their claims. Someone with mild iron deficiency can post an HbA1c several tenths higher than their actual glucose exposure warrants. If your HbA1c and fasting glucose tell different stories, check your iron studies before you change your diet.

The marketed ranges, examined

Each claim gets its strongest possible case before it gets its criticism. Several of these are substantially correct.

Under 5.3%

Promoted by longevity platforms and continuous glucose monitor programs

CConfounded

The strongest case for it

Risk of cardiovascular and microvascular disease rises continuously below the diagnostic cutoff, so a value of 5.6% is not equivalent to 5.0% even though both are labelled normal.

What it leaves out

HbA1c is a function of red blood cell lifespan as much as of glucose. Anemia, iron deficiency, hemoglobin variants, recent blood donation, and altitude all shift it independently of glycemia. Below the diagnostic range, much of the variation between people reflects hematology rather than metabolic health.

Before you act on your result

Unreliable in anemia, hemoglobinopathies, recent transfusion, or blood donation.
Reflects an average and conceals variability; two people with the same HbA1c can have very different glucose excursions.
Should be interpreted alongside fasting glucose and fasting insulin, never alone.

Last reviewed July 28, 2026How we grade evidence and attribute claims →

More in Metabolic

Fasting Glucose

Fasting Insulin

HOMA-IR

Insulin resistance index

Uric Acid

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