Prediabetes is diagnosed when your blood sugar levels are higher than normal but not yet high enough to qualify as type 2 diabetes. Three different blood tests can identify it, each with its own numerical range: an A1C between 5.7% and 6.4%, a fasting blood glucose between 100 and 125 mg/dL, or a two-hour glucose tolerance result between 140 and 199 mg/dL. Any one of these results landing in the prediabetic range is enough for a diagnosis.
The Three Tests and Their Ranges
Your doctor may use one or more of these tests to check for prediabetes. Each measures blood sugar in a different way, and the ranges for normal, prediabetic, and diabetic results are distinct.
A1C (hemoglobin A1C): This test reflects your average blood sugar over the past two to three months. A result below 5.7% is normal. Between 5.7% and 6.4% is prediabetes. At 6.5% or above, it’s diabetes. No fasting is required.
Fasting plasma glucose (FPG): This measures your blood sugar after you haven’t eaten for 8 to 12 hours. Below 100 mg/dL is normal. Between 100 and 125 mg/dL is prediabetes. At 126 mg/dL or higher, it’s diabetes.
Oral glucose tolerance test (OGTT): You fast overnight, then drink a sugary solution at the lab. Your blood is drawn two hours later. Below 140 mg/dL is normal. Between 140 and 199 mg/dL is prediabetes. At 200 mg/dL or above, it’s diabetes.
These same ranges apply to children and adolescents. There is no separate pediatric threshold.
Why Results Can Vary Between Tests
It’s possible to get a prediabetic result on one test and a normal result on another. That’s because each test captures something slightly different. Fasting glucose tells you how well your body manages sugar overnight. The glucose tolerance test reveals how efficiently your body clears a large dose of sugar. And the A1C gives a broader, longer-term picture.
Some people have trouble with fasting glucose specifically, while their body handles a sugar load just fine, or vice versa. Doctors sometimes use the terms “impaired fasting glucose” (when fasting levels are 100 to 125 mg/dL) and “impaired glucose tolerance” (when the two-hour test falls between 140 and 199 mg/dL) to distinguish between these patterns. Having both at the same time carries a higher risk of progressing to diabetes than having just one.
When A1C Results Can Be Misleading
The A1C test is convenient because it doesn’t require fasting and reflects a longer time window. But certain conditions can throw the number off. Iron deficiency anemia, vitamin B12 deficiency, kidney disease, and certain blood disorders can all cause falsely high or falsely low A1C readings. Pregnancy affects it too. Low iron stores in particular tend to push A1C results artificially higher, which could make a non-diabetic person look prediabetic on paper.
If you have any of these conditions, your doctor may rely more heavily on fasting glucose or the oral glucose tolerance test for an accurate picture.
International Differences in the Cutoff
Not every health organization draws the line in the same place. The American Diabetes Association sets the fasting glucose threshold for prediabetes at 100 mg/dL. The World Health Organization uses a higher cutoff of 110 mg/dL. The WHO also does not use the A1C test for prediabetes screening at all. This means that someone with a fasting glucose of, say, 105 mg/dL would be considered prediabetic under ADA criteria but normal under WHO criteria. If you’re comparing results across different countries or guidelines, this discrepancy is worth knowing about.
What to Know Before a Fasting Test
If you’re scheduled for a fasting glucose or glucose tolerance test, you’ll need to go without food for 8 to 12 hours beforehand. Water is fine, but coffee, juice, soda, and flavored water are not, since they can affect your results. You should also avoid chewing gum, smoking, and exercise during the fasting period. Most people schedule these tests first thing in the morning so the fasting window overlaps with sleep.
How Likely Prediabetes Is to Progress
Prediabetes is not a guarantee of type 2 diabetes, but without changes it does carry real risk. Roughly 5 to 10% of people with prediabetes develop type 2 diabetes each year. Over five years, that cumulative risk adds up significantly. The good news is that progression is not a one-way street. Many people move back to normal blood sugar levels, especially with lifestyle changes.
Physical Signs to Watch For
Prediabetes itself rarely causes obvious symptoms, which is why blood testing is so important. But insulin resistance, the underlying metabolic problem driving prediabetes, sometimes leaves visible clues. The most recognizable is patches of dark, thick, velvety skin that develop in body folds like the armpits, groin, or back of the neck. This condition, called acanthosis nigricans, develops slowly and can also come with skin tags or mild itching. It’s not dangerous on its own, but it signals that your body is producing more insulin than normal to keep blood sugar in check.
Reducing the Risk of Type 2 Diabetes
The most well-studied approach to reversing prediabetes is modest weight loss combined with regular physical activity. The landmark Diabetes Prevention Program found that losing just 5 to 7% of body weight (about 10 to 14 pounds for someone weighing 200 pounds) paired with 150 minutes of physical activity per week dramatically cuts the risk of developing type 2 diabetes. Participants who hit the 150-minute activity mark and attended structured support sessions had about a 50% success rate at reaching their weight loss target.
These don’t have to be extreme changes. Walking counts. The activity doesn’t need to happen all at once. And the weight loss goal is intentionally modest because even small reductions in body fat improve how well your cells respond to insulin. For many people, prediabetes is the stage where these changes have the greatest impact, before the pancreas has been under strain long enough to lose its ability to keep up with demand.