Prediabetes is diagnosed when your fasting blood sugar falls between 100 and 125 mg/dL. That’s above the normal range (under 100 mg/dL) but below the diabetes threshold of 126 mg/dL. Fasting blood sugar isn’t the only test used, though. There are three different measurements that can flag prediabetes, each capturing a slightly different picture of how your body handles sugar.
The Three Tests and Their Ranges
Any one of these three results is enough to indicate prediabetes:
- Fasting blood sugar (fasting plasma glucose): 100 to 125 mg/dL, measured after at least 8 hours without eating.
- A1C: 5.7% to 6.4%. This reflects your average blood sugar over the past two to three months, so it doesn’t require fasting.
- Oral glucose tolerance test (OGTT): 140 to 199 mg/dL two hours after drinking a sugary solution in a clinical setting.
These thresholds come from the American Diabetes Association and remain the current standard. At or above the top of each range, the diagnosis shifts to type 2 diabetes. Your doctor may use any of these tests, though fasting blood sugar and A1C are the most common in routine screening because they’re simple and don’t require a special appointment.
It’s worth knowing that the tests don’t always agree. You might have a normal fasting blood sugar but an A1C in the prediabetic range, or vice versa. If one test comes back borderline, a repeat test or a second type of test can clarify the picture.
What’s Happening in Your Body
Prediabetes means your cells are starting to resist insulin, the hormone that moves sugar from your blood into your muscles, fat, and liver. When those cells stop responding well, your pancreas compensates by producing more insulin. For a while, that extra effort keeps your blood sugar close to normal. But eventually the pancreas can’t keep up, and sugar begins to accumulate in your bloodstream. That’s when your numbers start creeping into the prediabetic range.
This process typically unfolds over years, not weeks. Most people with prediabetes feel completely fine, which is why routine screening matters. The condition rarely causes noticeable symptoms on its own.
Physical Signs You Might Notice
While prediabetes itself is usually silent, insulin resistance can leave a visible clue: dark, velvety patches of skin in body folds like the neck, armpits, or groin. This is called acanthosis nigricans. It’s common in people with obesity and signals that insulin levels have been elevated for a while. Not everyone with prediabetes develops these patches, but if you notice them, they’re a good reason to get your blood sugar checked.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends screening for prediabetes and type 2 diabetes in adults aged 35 to 70 who are overweight or obese (a BMI of 25 or higher). For Asian Americans, screening is recommended at a BMI of 23 or higher because diabetes risk rises at a lower body weight in this population. For Black, Hispanic/Latino, American Indian/Alaska Native, and Native Hawaiian/Pacific Islander adults, screening at an earlier age is encouraged because these groups develop diabetes at disproportionately higher rates.
If you don’t fall into those categories but have a family history of diabetes, a history of gestational diabetes, or polycystic ovary syndrome, your doctor may still recommend testing.
How Likely Prediabetes Is to Progress
Prediabetes is not a guaranteed path to type 2 diabetes, but it’s a serious risk signal. Roughly 5 to 10 percent of people with prediabetes develop type 2 diabetes each year if nothing changes. A large pooled analysis of 19 cohort studies found that after five years, about 8 percent of younger men with prediabetes had progressed to diabetes, while nearly 38 percent had reverted to normal blood sugar. Just over half remained in the prediabetic range.
Those numbers highlight an important point: prediabetes can go in either direction. What you do next has a significant effect on which way it goes.
How to Lower Your Risk
The strongest evidence for reversing prediabetes comes from the Diabetes Prevention Program, a landmark trial that tested modest lifestyle changes against medication and a control group. Participants who lost 5 to 7 percent of their body weight (about 10 to 14 pounds for a 200-pound person) and exercised at moderate intensity for at least 150 minutes per week reduced their risk of developing type 2 diabetes by 58 percent. That’s walking briskly for about 30 minutes, five days a week.
The weight loss doesn’t need to be dramatic. Losing even a small amount of weight improves how your cells respond to insulin. The exercise itself also helps, independent of weight loss, because working muscles pull sugar out of the blood more efficiently. Dietary changes that reduce refined carbohydrates and added sugars make the biggest difference for blood sugar control, though the research supports overall calorie reduction rather than any single diet.
Damage That Can Start Before Diabetes
One common misconception is that prediabetes is harmless, a “pre” condition that only matters if it progresses. Research published in BMJ Open Diabetes Research & Care found that people who had prediabetes before eventually being diagnosed with type 2 diabetes already showed measurable harm at the time of their diabetes diagnosis. Compared to those who had normal blood sugar before diagnosis, the prediabetes group had 14 percent higher odds of kidney damage and 7 percent higher odds of having experienced an acute coronary event like a heart attack.
These aren’t large increases, but they demonstrate that mildly elevated blood sugar isn’t benign over time. Blood vessels and kidneys are sensitive to even modest, sustained rises in blood sugar. This is one reason guidelines encourage treating prediabetes as a condition worth acting on, not just monitoring.
What Your Numbers Mean in Practice
If your fasting blood sugar comes back at 100 or 101 mg/dL, you’re technically in the prediabetic range but at the low end. A reading of 120 mg/dL puts you much closer to the diabetes threshold. The same gradient applies to A1C: 5.7% is early prediabetes, while 6.3% is right at the edge of a diabetes diagnosis. Your doctor will consider where you fall within the range, not just whether you’ve crossed into it.
Retesting matters too. A single elevated reading can reflect stress, illness, poor sleep the night before, or a lab variation. Guidelines generally call for a confirmatory test before making the diagnosis, especially if the result is borderline. If your number is confirmed, the typical next step is a conversation about lifestyle changes and a follow-up test in three to six months to see whether your levels are moving in the right direction.