A1c

What does an A1c of 5.7 mean?

By GyroscopeUpdated November 14, 20267 sources

It’s the first number of the prediabetes range, which runs from 5.7 to 6.4%. An A1c of 5.7% (39 mmol/mol) matches an average blood sugar near 117 mg/dL over the last few months. It isn’t diabetes, and it’s the best time to find out. Change your habits now and retest in about 3 months, at the same lab.

Why 5.7 sounds harmless

The diabetes line is 6.5%, and 5.7 is a long way from it, so it’s easy to file away as “a bit high”, and nothing feels any different. But the American Diabetes Association counts 5.7 to 6.4% as the prediabetes range, and people in it are asked to test every year.

What A1c is

Sugar in your blood sticks to hemoglobin, the protein that carries oxygen in your red cells. A1c is the share of your hemoglobin with sugar stuck to it. The more sugar in your blood, and the longer a cell has been around, the more it picks up. In people without diabetes, the average red cell in the blood was 38 to 60 days old.

A1c works like a tan. It shows the last few months of sun, the latest weeks most, and one beach day barely shows. In 9 people newly diagnosed with type 2, A1c reflected about the last 100 days of blood sugar, weighted most heavily to the days just before the test.

What 5.7 means in blood sugar

The study that built the conversion followed 507 adults for 3 months each, with sensors and finger sticks. Average glucose (mg/dL) = 28.7 × A1c − 46.7.

The range is wide. In that study, an A1c of 6% fit averages anywhere from 100 to 152 mg/dL. Part of the reason is that red cells live longer in some people than others, and in a small study that difference alone was enough to shift A1c for the same blood sugar.

A1c can be wrong for your blood

Anemia, iron levels, recent blood loss, a transfusion, some hemoglobin variants such as sickle cell trait, G6PD deficiency, HIV medicines and pregnancy can all throw it off (American Diabetes Association, 2026). On average, Black adults have A1c values about 0.3 points higher, a finding the ADA calls controversial. That’s why a fasting glucose belongs beside it.

What happens next

In the Diabetes Prevention Program, 3,234 adults with raised blood sugar who aimed to lose 7% of their weight and move 150 minutes a week cut new diabetes by 58% over about 3 years. How do I reverse prediabetes? lays out that plan by week. A1c takes about 3 months to show most of a change, so a retest at 12 weeks is the one to trust.

One surprise if you wear a sensor: a healthy person’s sensor average of 98 mg/dL turns into a GMI of 5.7%, the same number, because the GMI formula and the sensor both run high. That’s not your lab A1c, and why GMI and A1c differ explains it. Every A1c from 4.5 to 10 has its own page, like 5.8 and 6.0.