What is a good A1C? The ranges the ADA actually defines

What the ranges are, and what they are not

The ADA publishes three ranges on the A1C scale, and the phrasing it uses matters. Below 5.7% sits under the range the ADA calls prediabetes. From 5.7% to 6.4% is that prediabetes range. From 6.5% upward is a range the ADA uses as one criterion for diagnosing diabetes, normally requiring either a repeat abnormal test or one abnormal test alongside unambiguous symptoms. None of those is a statement about you: they are boundaries drawn on a number line, and where your own result sits relative to them is information for a conversation, not a verdict delivered by a web page.

On "A1C by age"

This is one of the most-searched phrasings in the whole A1C cluster, and it deserves a straight answer: the ADA does not publish a table of normal A1C ranges by age in the way the phrase implies. What clinical guidance does say is that glycemic targets for people already diagnosed with diabetes are individualised — the ADA explicitly discusses relaxing targets for older adults with multiple coexisting conditions, limited life expectancy, or a meaningful risk of hypoglycaemia, because in those situations the harms of tight control can outweigh the benefits. That is individualisation of a treatment target by clinical circumstance, which is a different thing from an age-banded normal range, and any site that hands you one is inventing it.

Why a value near a boundary deserves less weight, not more

People search hardest about values a tenth or two from a threshold — 5.6% and 5.8%, or 6.4% and 6.5%. The uncomfortable fact is that this is exactly where a single number tells you least. NGSP certification allows a certified assay to sit about half a percentage point either side of the reference method, which is wider than the gap you are worrying about. Two draws from the same person in the same week can straddle a boundary without anything having changed. This is precisely why the ADA asks for confirmation before diagnosing, and why a trend across tests is worth more than any one result.

What A1C does not see

A1C is an average, and averages hide shape. Two people with identical A1C values can have very different daily glucose ranges, one steady and one swinging widely, and A1C will not distinguish them. Conditions that change the lifespan of red blood cells — anaemia, recent blood loss, some haemoglobin variants, pregnancy, chronic kidney disease — shift A1C independently of glucose, in either direction. If any of those apply to you, the number needs interpreting rather than reading, and that interpretation is your clinician's job.

Official sources

• American Diabetes Association — Standards of Care in Diabetes
• Nathan et al., Translating the A1C Assay Into Estimated Average Glucose Values, Diabetes Care 2008
• NGSP — A1C method certification criteria

Frequently asked questions