Prediabetes rarely announces itself with obvious symptoms. Most of the 98 million American adults who have it don’t know it. The most reliable way to find out is a simple blood test, but certain physical signs, risk factors, and lifestyle patterns can tell you whether testing should be a priority.
What the Blood Tests Actually Measure
Three blood tests can identify prediabetes, and your doctor may use any one of them. The most common is the A1C test, which measures your average blood sugar over the past two to three months. An A1C between 5.7% and 6.4% falls in the prediabetes range. Below 5.7% is normal, and 6.5% or higher indicates diabetes.
A fasting plasma glucose test measures your blood sugar after you haven’t eaten for at least eight hours. A result between 100 and 125 mg/dL signals prediabetes. The third option, an oral glucose tolerance test, checks your blood sugar two hours after drinking a sugary solution. A reading between 140 and 199 mg/dL puts you in the prediabetes range.
These tests don’t always agree with each other. You could have a normal A1C but elevated fasting glucose, or vice versa. If one test comes back borderline, your doctor will likely repeat it or run a second type of test to confirm.
When A1C Results Can Be Misleading
The A1C test works by measuring how much sugar is attached to your red blood cells. Anything that changes how long your red blood cells survive or how quickly your body makes new ones can skew the number. Iron deficiency anemia and vitamin deficiency anemia tend to push A1C results artificially higher, which could make your blood sugar look worse than it is. Conditions that destroy red blood cells faster than normal, like hemolytic anemia, have the opposite effect and can make results look falsely low.
Chronic kidney disease, liver disease, and certain inherited hemoglobin variants also affect accuracy. Pregnancy changes red blood cell turnover enough to make A1C unreliable for many women. If you have any of these conditions, your doctor may rely more heavily on fasting glucose or glucose tolerance testing instead.
Physical Signs You Might Notice
Most people with prediabetes feel completely fine, which is what makes it so easy to miss. But insulin resistance, the metabolic problem behind prediabetes, sometimes leaves visible clues on your skin.
The most recognizable one is dark, thick, velvety patches of skin that develop slowly in body folds: the back of the neck, armpits, and groin are the most common spots. This condition, called acanthosis nigricans, happens because excess insulin in the bloodstream stimulates skin cells to reproduce faster than normal. The affected skin may feel slightly itchy or develop small skin tags. These patches aren’t dangerous on their own, but they’re a strong visual signal that your body is struggling to use insulin effectively.
Other subtle changes that sometimes accompany insulin resistance include increased thirst, more frequent urination, blurry vision, and fatigue. These overlap heavily with early type 2 diabetes symptoms, so if you’re noticing them, testing sooner rather than later makes sense.
Risk Factors That Raise Your Odds
Your body composition is one of the strongest predictors. A BMI of 25 or higher increases your risk significantly, though the threshold varies by ethnicity. For Asian Americans, a BMI of 23 or higher carries elevated risk. For Pacific Islanders, the cutoff is 26. Where you carry weight matters too. Men with a waist circumference over 40 inches and women with a waist over 35 inches face higher risk, because abdominal fat is more metabolically active and more likely to drive insulin resistance than fat stored in the hips or thighs.
Beyond weight, several other factors stack the odds:
- Family history: a parent or sibling with type 2 diabetes
- Age: risk climbs after 35, though prediabetes is increasingly common in younger adults
- Sedentary lifestyle: being physically active fewer than three times a week
- Race and ethnicity: Black, Hispanic, Native American, Asian American, and Pacific Islander populations face higher rates
- Sleep disorders: obstructive sleep apnea is independently linked to insulin resistance
For women specifically, two conditions stand out. A history of gestational diabetes during pregnancy significantly increases the chance of developing prediabetes or type 2 diabetes later in life. And polycystic ovary syndrome (PCOS) carries one of the steepest risks of any related condition: more than half of women with PCOS develop type 2 diabetes by age 40.
At-Home A1C Kits: Are They Reliable?
Over-the-counter A1C test kits are widely available at pharmacies and online, but their accuracy is inconsistent. A study of 219 people compared several popular home kits against standard lab results. To be considered accurate, a home test needs to land within 5% of the lab value at least 90% of the time. Only one kit, called Home Access, came close, with 82% of samples meeting that benchmark. Two other widely sold kits, A1cNow+ and CoreMedica, hit the accuracy target in only 46% and 29% of samples.
A home kit can give you a rough idea of where you stand, but the margin of error is wide enough that a result in the 5.5% to 6.5% range could easily be off by enough to matter. If your home test shows anything near the prediabetes threshold, follow up with a lab-drawn test. And if you have risk factors for prediabetes, skip the home kit and go straight to your doctor for proper testing.
How Often to Get Tested
The American Diabetes Association recommends screening for adults who are overweight and have at least one additional risk factor, regardless of age. For everyone else, routine screening is recommended starting at age 35. If your results come back normal, retesting every three years is generally sufficient.
If you’re already diagnosed with prediabetes, the timeline tightens. You should be retested every one to two years, because roughly 15% to 30% of people with prediabetes progress to type 2 diabetes within five years without intervention. The flip side is encouraging: prediabetes is one of the most reversible metabolic conditions. Losing 5% to 7% of your body weight and getting 150 minutes of moderate physical activity per week reduces the risk of progression by more than half.
Putting the Pieces Together
If you’re reading this article, you probably have a reason to wonder. Maybe your weight has crept up, a family member was diagnosed, or a routine blood test came back with a number that caught your eye. The clearest answer comes from a lab test, but you can gauge your own risk level right now by looking at the factors above. If two or more apply to you, or if you’ve noticed darkened skin patches in your neck folds or armpits, getting tested is a straightforward next step. A standard fasting glucose or A1C test is inexpensive, widely available, and gives you a definitive answer within days.