Diabetes often develops without obvious warning signs, and roughly 45% of people living with it worldwide don’t know they have it. The only definitive way to know is through a blood test, but your body does send signals, some subtle and some hard to miss, that suggest your blood sugar is running too high. Knowing what to look for and when to get tested can make a significant difference in catching it early.
The Most Common Warning Signs
When blood sugar stays elevated, your kidneys work overtime trying to filter the excess glucose. When they can’t keep up, the extra sugar spills into your urine and pulls fluid from your tissues along with it. That’s why the earliest and most recognizable signs of diabetes are urinating far more often than usual and feeling constantly thirsty. You drink more to compensate for the fluid loss, which leads to even more urination. It becomes a cycle that’s hard to ignore once it gets going.
Other symptoms that commonly show up together include:
- Unexplained weight loss, even when you’re eating more than usual. Your cells can’t access glucose properly, so your body starts burning fat and muscle for energy.
- Persistent fatigue that doesn’t improve with rest, because your cells are starved for fuel.
- Blurred vision, caused by fluid shifts in the lens of your eye when blood sugar swings.
- Tingling or numbness in your hands or feet, a sign that elevated sugar is affecting your nerves.
- Slow-healing cuts or sores, because high glucose impairs circulation and immune response.
- Frequent infections, particularly urinary tract infections, yeast infections, or skin infections.
How quickly these symptoms appear depends on the type of diabetes. In type 1, which is more common in children and young adults, symptoms develop fast, sometimes within weeks. In type 2, the far more common form, symptoms creep in so gradually over months or years that many people dismiss them as normal aging or stress.
Skin Changes That Signal Insulin Resistance
Your skin can reveal problems with blood sugar long before other symptoms become noticeable. One of the most telling signs is acanthosis nigricans: dark, velvety patches of skin that appear in body creases like the neck, armpits, or groin. These patches indicate insulin resistance, meaning your body is producing insulin but not using it effectively. Acanthosis nigricans can appear during prediabetes, well before a full diabetes diagnosis.
Other skin-related signs include shin spots (flat red or brown patches on the lower legs that don’t hurt or itch), frequent bacterial infections that cause swollen, red, painful skin around hair follicles or fingernails, and recurring fungal infections like athlete’s foot, jock itch, or vaginal yeast infections. These infections thrive when blood sugar is elevated because glucose feeds the organisms responsible. If you’re getting these infections more often than seems normal, it’s worth checking your blood sugar.
Who Should Get Tested
Both the American Diabetes Association and the U.S. Preventive Services Task Force recommend screening starting at age 35 for adults who are overweight or obese, with repeat testing every three years. The ADA also recommends that any adult with overweight or obesity plus at least one additional risk factor be screened regardless of age.
Those additional risk factors include a family history of diabetes (especially a parent or sibling), a sedentary lifestyle, a history of gestational diabetes, polycystic ovary syndrome, high blood pressure, or belonging to a racial or ethnic group with higher rates of diabetes, including Black, Hispanic, Native American, Asian American, and Pacific Islander populations. If any of these apply to you, don’t wait for symptoms to appear. Many people with type 2 diabetes have no symptoms at the time of diagnosis.
The Tests That Confirm a Diagnosis
Three main blood tests are used to diagnose diabetes, and each measures blood sugar in a different way. Your doctor may use one or a combination, and an abnormal result is typically confirmed with a second test on a different day.
A1C Test
This test measures your average blood sugar over the past two to three months. It doesn’t require fasting. The results break down like this:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
Fasting Blood Sugar Test
You fast overnight (at least eight hours), then have your blood drawn. This gives a snapshot of your glucose level without the influence of recent meals:
- Normal: 99 mg/dL or below
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher
Glucose Tolerance Test
This one also starts with a fasting blood draw. Then you drink a sugary solution, and your blood is tested again two hours later to see how well your body handles the sugar load:
- Normal: 140 mg/dL or below at two hours
- Prediabetes: 140 to 199 mg/dL
- Diabetes: 200 mg/dL or higher
There’s also the random blood sugar test, which can be done at any time without fasting. A result of 200 mg/dL or higher, combined with classic symptoms like excessive thirst and frequent urination, is enough to diagnose diabetes on the spot.
Can You Test at Home?
Over-the-counter blood glucose monitors (the finger-prick devices sold at pharmacies) can give you a general idea of where your blood sugar sits, but they aren’t designed for diagnosis. The FDA allows these devices a margin of error of 15 to 20% above or below the actual reading. That means a true blood sugar of 120 mg/dL could show up anywhere from about 96 to 144 on a home meter. That’s a range that spans from normal to solidly in prediabetes territory.
A home reading can be a useful nudge to get proper lab work done, especially if the number comes back high. But a normal reading on a home meter doesn’t rule anything out, and a single high reading doesn’t confirm diabetes. Lab testing through a healthcare provider is the only reliable path to diagnosis.
Prediabetes: The Window You Don’t Want to Miss
Prediabetes means your blood sugar is elevated but hasn’t crossed the threshold for a diabetes diagnosis. It’s not a mild or harmless condition. Without changes, a significant portion of people with prediabetes will progress to type 2 diabetes within several years. The good news is that prediabetes responds well to lifestyle changes. Losing even 5 to 7% of your body weight (about 10 to 14 pounds for someone who weighs 200) and getting 150 minutes of moderate physical activity per week can dramatically reduce the risk of progression.
The tricky part is that prediabetes almost never causes noticeable symptoms. The skin changes mentioned earlier, particularly dark patches on the neck or armpits, are one of the few visible clues. This is exactly why routine screening matters so much for people with risk factors. Catching prediabetes gives you a window to reverse course that disappears once full diabetes develops.
Type 1 vs. Type 2: Different Paths to Diagnosis
Type 1 diabetes is an autoimmune condition where the body attacks the cells that produce insulin. It most often appears in children and young adults, and its symptoms develop quickly, sometimes over just a few weeks. The rapid onset means type 1 is often caught in an emergency setting, with severe symptoms like vomiting, rapid breathing, or extreme fatigue. If you’re an adult wondering whether you might be diabetic, type 2 is statistically far more likely, accounting for about 90 to 95% of all cases.
Type 2 develops when your body becomes resistant to insulin or doesn’t produce enough of it. Because this process unfolds slowly, you can have elevated blood sugar for years with no obvious symptoms. The damage, however, is already happening. Uncontrolled blood sugar quietly affects your blood vessels, nerves, kidneys, and eyes long before you feel anything wrong. That gap between the start of the disease and the moment you notice something is why nearly half of all people with diabetes are undiagnosed.