An A1c between 5.7 and 6.4: what does the gray zone actually mean?

What does an A1c of 5.7 to 6.4 mean?

It means that, averaged over the past few months, blood sugar has been higher than in most healthy adults and lower than the level used to diagnose diabetes. Prediabetes is the name for that middle band, and it describes risk, not damage already done.

A1c, short for hemoglobin A1c, measures the share of hemoglobin, the oxygen-carrying protein in red blood cells, that has glucose attached. Red blood cells live for about 120 days, so the result works as a running average over roughly that span, weighted toward the most recent weeks. The A1c band is one of three ways guidelines define prediabetes. The other two are a fasting glucose of 100 to 125 mg/dL and a reading of 140 to 199 mg/dL two hours into a glucose tolerance test [Source: ADA 2024 Standards of Care, Classification and Diagnosis of Diabetes].

The label is common and less fixed than it sounds. About 1 in 3 US adults has prediabetes [PMID: 37039787]. Each year roughly 5 to 10 percent of people with it go on to diabetes, and a similar share return to normal glucose levels [PMID: 22683128].

Where the number sits inside the band matters. In a systematic review, 25 to 50 percent of people with an A1c of 6.0 to 6.5 developed diabetes within five years, compared with 9 to 25 percent of those between 5.5 and 6.0 [PMID: 20587727]. A 5.7 and a 6.4 share a label, not the same odds.

What does A1c miss, and what can distort it?

A1c is a convenient, stable test that needs no fasting, but it misses the shape of the day, and anything that changes red blood cells can push it up or down.

An average hides swings. Two people can share the same A1c, one with level glucose and one with sharp rises after meals. When researchers put continuous glucose sensors on adults whose standard tests were normal, glucose still reached the range associated with prediabetes about 15 percent of the time [PMID: 30040822].

The other limit is the red blood cell itself. Iron deficiency, with or without anemia, tends to raise A1c with no change in blood sugar [PMID: 25994072]. Recent blood loss or a transfusion, some inherited hemoglobin variants, pregnancy and dialysis also alter the relationship between A1c and glucose, and in those settings guidelines rely on glucose measurements instead. The same guidelines note that A1c is less sensitive than glucose tests at the diagnostic line, and that a marked mismatch between the two should raise the question of interference [Source: ADA 2024 Standards of Care, Classification and Diagnosis of Diabetes].

What usually comes next after an A1c in this range?

What usually comes next is confirmation, then a short list of tests and questions that show why the number sits where it does.

• Confirmation. A repeat A1c or a fasting glucose, with a blood count and iron studies when there is reason to doubt the A1c itself
• Fasting insulin. It shows how much insulin the pancreas, the organ behind the stomach that makes it, needs to keep glucose in range. A high value beside a borderline A1c points to insulin resistance, where cells respond weakly to insulin
• An oral glucose tolerance test. Blood is drawn fasting and again two hours after a measured sugar drink. It shows how the body handles a glucose load, which neither a fasting sample nor an average can
• A continuous glucose sensor. Worn for a short stretch and now sold over the counter, it shows how glucose behaves around real meals, exercise and sleep
• The markers that travel with glucose. Triglycerides and HDL cholesterol, the liver enzyme ALT, blood pressure and waist size, which insulin resistance tends to move together
• Anything pushing glucose up. Steroid medications and several other drug classes, short or broken sleep, untreated sleep apnea and a recent illness can all raise it

Guidelines then call for yearly testing once a result falls in this range [Source: ADA 2024 Standards of Care, Classification and Diagnosis of Diabetes].

What does a physician do with an A1c in the gray zone?

A physician reads the number against the person it belongs to: the history, the earlier results and the markers around it.

History sets the odds. A parent or sibling with type 2 diabetes, diabetes during a pregnancy, polycystic ovary syndrome, a hormonal and metabolic condition, weight that has moved to the midsection, loud snoring and certain medications all make a borderline A1c more likely to reflect insulin resistance. When none is present, a fair question is whether the A1c is accurate for this person. Direction matters as much as position: a value that has crept upward across three physicals is a trend, and one that has not moved in a decade is a set point.

Then comes the organizing question: what would change the plan? If fasting insulin and triglycerides are high, the driver is clear and a glucose tolerance test may add little. If everything around the A1c looks healthy, iron studies and a blood count may be the better next step. Decisions are made in coordination with the primary care physician, an endocrinologist or an OB-GYN when one is already involved. The same logic runs through what a prediabetes result changes, since the process behind the number is usually insulin resistance.

Can an A1c in this range come back down?

Often, yes. Numbers in this range respond to how a person eats, moves, sleeps and carries weight, and for some people to medication.

The strongest evidence is for structured lifestyle programs built around weight loss and regular physical activity, which lowered the rate of new diabetes in large trials [PMID: 37039787]. Returning to normal glucose seems to matter in its own right. In the long-term follow-up of the Diabetes Prevention Program, participants whose glucose returned to normal at least once had a 56 percent lower risk of later diabetes than those who stayed in the prediabetes range throughout, whichever treatment they had been assigned [PMID: 22683134].

The levers are familiar: building and keeping muscle, the body's largest destination for glucose after a meal; fewer refined carbohydrates and sweetened drinks; sufficient sleep, with sleep apnea treated when present; and less weight carried around the waist. Glucose-lowering medication has a place for some people, a decision that belongs inside a medical relationship.

When does blood sugar need prompt care?

An A1c in this range is not an emergency and causes no symptoms. Very high blood sugar is different: marked thirst, frequent urination, blurred vision or unexplained weight loss are reasons to seek prompt care, and when they come with vomiting, abdominal pain, deep rapid breathing, confusion or unusual drowsiness, the step is to call 911 or go to the nearest emergency department.

Can an A1c ordered without a physician be reviewed?

Yes. An A1c from a lab service a person ordered on their own, a workplace screening or a home collection kit is reviewed as part of care, though a fingerstick result is usually confirmed with a laboratory draw. The full report helps more than the single number: the date, the laboratory, and any glucose, insulin, lipid or blood count values drawn with it. Earlier results turn a snapshot into a trend.

The deeper picture

The gray zone is less a diagnosis than a moment in a long process. The body defends blood sugar tightly, so by the time the average drifts upward, insulin resistance and strain on the insulin-producing cells have usually been present for some time [PMID: 22683128], and the same process often shows in triglycerides, liver enzymes, blood pressure and the waistline. The number can be misread in two directions: as a disease, which it is not, or as nothing, because it is only borderline. Reading it well takes physician-level clinical rigor and one person's full history, which is how a result like this is approached at Extend Medical.