The only way to know for sure if you have diabetes is through a blood test, but your body often sends warning signs well before a diagnosis. About 4.5% of U.S. adults, roughly 1 in 22 people, are walking around with diabetes and don’t know it. Recognizing the early signals and understanding who should get tested can help you catch it sooner, when it’s most manageable.
The Three Classic Warning Signs
Diabetes revolves around your body’s inability to properly use glucose, the sugar that fuels your cells. When glucose builds up in your blood instead of getting into cells, three signature symptoms tend to appear together.
The first is frequent urination. Your kidneys work overtime to filter the excess sugar out of your blood, pulling extra water along with it. That leads to the second symptom: intense thirst, because your body is trying to replace all the fluid it’s losing. The third is increased hunger. Even though there’s plenty of glucose in your bloodstream, your cells aren’t getting enough of it, so your body signals you to eat more. These three symptoms, frequent urination, excessive thirst, and constant hunger, are the hallmark trio that doctors look for first.
Other Signs You Might Miss
Beyond those three, diabetes can show up in less obvious ways. Unexplained weight loss is common, especially with type 1 diabetes, because your body starts burning fat and muscle for energy when it can’t access glucose properly. Fatigue that doesn’t improve with rest is another frequent complaint. Cuts and sores that heal slowly, frequent infections (particularly yeast infections or urinary tract infections), and tingling or numbness in your hands or feet all point toward chronically elevated blood sugar.
Blurry vision catches many people off guard. Over time, high blood sugar damages the tiny blood vessels that nourish the retina at the back of your eye, and even in the early stages, fluctuating sugar levels can make your vision shift. If your eyesight suddenly becomes blurry, spotty, or hazy, that warrants prompt attention.
One subtle clue that appears before many other symptoms is a skin change called acanthosis nigricans: dark, thick, velvety patches of skin that develop slowly in body folds like the back of your neck, armpits, or groin. These patches sometimes itch or develop small skin tags. They signal insulin resistance, the underlying metabolic problem that leads to type 2 diabetes. People with these skin changes are significantly more likely to develop type 2 diabetes, so it’s worth mentioning to a doctor even if you feel fine otherwise.
Type 1 vs. Type 2: How Symptoms Differ
The timeline of symptoms depends heavily on which type of diabetes is developing. Type 1 diabetes, where the immune system destroys the cells that produce insulin, tends to come on fast. Symptoms can appear within days or weeks and are often severe enough to send someone to the hospital. While it’s most commonly diagnosed in children and young adults, it can start at any age.
Type 2 diabetes is far more gradual. Symptoms develop over several years, and many people have no noticeable symptoms at all during the early stages. That slow progression is exactly why so many cases go undiagnosed. Risk increases with age, particularly after 35, though children and teens can develop it too. Because type 2 accounts for the vast majority of cases and often hides in plain sight, screening is especially important for people with risk factors.
Who Should Get Tested
Current guidelines from the American Diabetes Association recommend that all adults get screened starting at age 35 and repeat the test every three years. If you’re younger than 35 but carry excess weight and have at least one additional risk factor, screening is also recommended. Those risk factors include a family history of diabetes, physical inactivity, a history of gestational diabetes, or belonging to certain higher-risk ethnic groups (African American, Hispanic, Native American, Asian American, or Pacific Islander).
You don’t need to wait for symptoms to appear. Given that nearly a third of all diabetes cases in the U.S. are currently undiagnosed, routine screening is one of the most effective ways to catch the disease early.
The Blood Tests That Confirm a Diagnosis
Three main blood tests are used to diagnose diabetes, and each measures blood sugar in a slightly different way.
- A1C test: This measures your average blood sugar over the past two to three months. No fasting required. An A1C below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher means diabetes.
- Fasting blood glucose: You fast for at least eight hours, then your blood sugar is measured. Below 100 mg/dL is normal, 100 to 125 mg/dL is prediabetes, and 126 mg/dL or higher is diabetes.
- Oral glucose tolerance test: After fasting for eight hours, your blood sugar is tested, then you drink a solution containing 75 grams of sugar. Your blood is drawn again one and two hours later. A two-hour reading below 140 mg/dL is normal, 140 to 199 mg/dL is prediabetes, and 200 mg/dL or higher is diabetes.
Doctors typically confirm the diagnosis with a second test on a different day, unless your blood sugar is extremely high and you already have obvious symptoms. The A1C test is the most convenient because it doesn’t require fasting, but any of these three tests can establish a diagnosis.
What Prediabetes Means for You
If your results land in the prediabetes range, that’s not a diagnosis of diabetes, but it is a clear signal that your blood sugar is higher than it should be. Prediabetes means your body is already struggling with insulin, and without changes, it frequently progresses to type 2 diabetes. The encouraging news is that prediabetes is the stage where lifestyle changes, such as losing a moderate amount of weight, increasing physical activity, and adjusting your diet, have the greatest impact on preventing or delaying a full diagnosis.
Emergency Symptoms That Need Immediate Care
In some cases, particularly with undiagnosed type 1 diabetes, blood sugar can spike dangerously high and trigger a condition called diabetic ketoacidosis (DKA). This happens when your body, starved for glucose, breaks down fat so rapidly that it floods your blood with acids called ketones.
Early signs of DKA overlap with general diabetes symptoms: extreme thirst and frequent urination. But as it progresses, more alarming symptoms appear quickly. These include fruity-smelling breath, nausea and vomiting, stomach pain, rapid deep breathing, dry skin and mouth, severe fatigue, and headache. DKA is a medical emergency. If you notice fruity-smelling breath, can’t keep food or liquids down, are having trouble breathing, or have a known blood sugar reading above 300 mg/dL, call 911 or get to an emergency room immediately.