The most reliable way to know if you’re diabetic is a blood test ordered by your doctor, but your body often sends signals before you ever get to a lab. Frequent urination, unusual thirst, and unexplained weight loss are the three hallmark signs of elevated blood sugar. Some people, though, have diabetes or prediabetes for years with no obvious symptoms at all, which is why screening matters even when you feel fine.
Symptoms That Signal High Blood Sugar
Type 1 and type 2 diabetes share a core set of symptoms: urinating more often than usual, feeling thirstier than normal, and losing weight without trying. These happen because your body can’t move sugar from your blood into your cells effectively. The excess sugar spills into your urine, pulling water with it, which makes you pee more and feel dehydrated. And because your cells aren’t getting the fuel they need, your body starts breaking down fat and muscle for energy, causing the weight loss.
Other common signs include blurry vision, slow-healing cuts or sores, tingling or numbness in your hands or feet, and feeling unusually tired. Some people notice more frequent infections, particularly yeast infections or urinary tract infections.
The speed at which symptoms appear depends on the type. Type 1 diabetes often comes on quickly, sometimes over just a few weeks, and the symptoms tend to be intense enough that they’re hard to ignore. Type 2 diabetes develops much more slowly. Symptoms creep in gradually and can be so mild in the early stages that many people chalk them up to aging, stress, or being out of shape. This is a big part of why type 2 often goes undiagnosed for years.
Physical Signs You Can See
Your skin can offer visible clues. A condition called acanthosis nigricans causes dark, velvety patches of skin in body creases, most commonly on the neck, armpits, or groin. It sometimes appears on the hands, elbows, or knees. These patches are a sign of insulin resistance, which means your body is producing insulin but struggling to use it properly. Acanthosis nigricans is common in people with obesity and can indicate prediabetes or type 2 diabetes.
Skin tags, frequent skin infections, and wounds that take longer than expected to heal are also worth paying attention to. None of these confirm diabetes on their own, but they’re reasons to get tested.
Prediabetes Often Has No Symptoms
Prediabetes is the stage where your blood sugar is higher than normal but not yet high enough for a diabetes diagnosis. The tricky part: it usually causes no signs or symptoms at all. The one possible exception is darkened skin patches (acanthosis nigricans), particularly on the neck, armpits, and groin. Without lifestyle changes, people with prediabetes are at high risk of developing type 2 diabetes. That’s why screening based on risk factors is so important, even if you feel perfectly healthy.
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. “Overweight” in this context means a BMI of 25 or higher. If you’re Asian American, screening is recommended at a lower BMI threshold of 23, because the risk of diabetes rises at a lower body weight in this population.
Earlier screening is also recommended if you belong to a group with a disproportionately high rate of diabetes, including American Indian/Alaska Native, Black, Hispanic/Latino, and Native Hawaiian/Pacific Islander communities. A family history of diabetes, a history of gestational diabetes, or a diagnosis of polycystic ovary syndrome are additional reasons to get tested sooner.
The Three Main Diagnostic Tests
Diabetes is diagnosed through blood tests, not symptoms alone. Three tests are standard, and any one of them can confirm a diagnosis.
- A1C test. This measures your average blood sugar over the past two to three months. A result of 6.5% or higher indicates diabetes. No fasting is required, which makes it the most convenient option.
- Fasting blood sugar test. You fast for at least eight hours (usually overnight), then have your blood drawn. A result of 126 mg/dL or higher means diabetes.
- Glucose tolerance test. After fasting overnight, you have your blood drawn, then drink a sugary solution containing 75 grams of sugar. Your blood is drawn again two hours later. A two-hour result of 200 mg/dL or higher indicates diabetes.
If a result comes back in the diabetes range, your doctor will typically repeat the test on a different day to confirm. The exception is if you already have clear symptoms of high blood sugar and a random blood sugar reading above 200 mg/dL, which can be enough for a diagnosis on its own.
Can You Test Yourself at Home?
Home blood glucose monitors (glucometers) are widely available at pharmacies, and it’s tempting to use one to check your own levels. While a home reading can give you a rough idea of where your blood sugar stands, it’s not considered a reliable way to diagnose diabetes. Glucometer readings can vary by 10 to 15% compared to laboratory results, and those readings tend to run higher than lab values. At the borderline between normal, prediabetes, and diabetes, that margin of error is enough to cause a misclassification in either direction.
Home monitors are excellent tools for people who already have a diagnosis and need to track their blood sugar day to day. But for an initial diagnosis, a lab-based blood test is the standard. If a home reading concerns you, use it as motivation to schedule a proper lab test rather than treating it as a final answer.
What a Diagnosis Actually Looks Like
Many people expect a dramatic moment, but a diabetes diagnosis usually comes from routine bloodwork or a screening test at a regular checkup. You might have no symptoms at all, especially with type 2. Your doctor runs an A1C or fasting glucose, the number comes back elevated, and a repeat test confirms it. For type 1, the onset is typically more acute: you feel noticeably sick, go to the doctor or emergency room, and blood tests quickly reveal very high blood sugar levels.
If your results fall in the prediabetes range (an A1C between 5.7% and 6.4%, or a fasting glucose between 100 and 125 mg/dL), that’s not a diabetes diagnosis, but it’s a clear signal that your body is already struggling with blood sugar regulation. At that stage, changes to diet, physical activity, and weight can significantly reduce the risk of progressing to type 2 diabetes.