The only way to know for sure if you have diabetes is through a blood test, but your body often sends warning signs worth paying attention to. More than 115 million American adults have prediabetes, and 8 in 10 of them don’t know it. That means millions of people are living with elevated blood sugar right now without any obvious symptoms. Whether you’ve noticed changes in your body or simply have risk factors that concern you, here’s how to figure out where you stand.
Symptoms That Suggest High Blood Sugar
The three classic symptoms of diabetes are frequent urination, increased thirst, and unexplained weight loss. These are connected: when blood sugar stays too high, your kidneys work overtime to filter out the excess glucose, pulling extra water from your body. You urinate more, you get dehydrated, and you feel thirsty constantly. Meanwhile, your cells aren’t getting the energy they need from glucose, so your body starts breaking down fat and muscle for fuel, causing you to lose weight without trying.
Beyond those three hallmarks, there are subtler signs that often go unnoticed or get blamed on something else:
- Blurry vision that comes and goes
- Slow-healing cuts or sores that linger for weeks
- Frequent infections, particularly of the gums, skin, or vaginal area
- Increased hunger even after eating
- Fatigue that doesn’t improve with rest
These secondary signs can appear months or even years before someone gets a diagnosis, especially with type 2 diabetes. Many people dismiss them as aging, stress, or poor sleep.
How Symptoms Differ by Type
Type 1 and type 2 diabetes share many of the same symptoms, but the timeline is very different. Type 1 symptoms develop fast, usually over a few days to weeks. Type 2 symptoms can creep in slowly over several years, which is why so many cases go undetected.
Type 1 diabetes sometimes announces itself through a dangerous condition called diabetic ketoacidosis, or DKA. When the body can’t use glucose for energy (because it’s not producing insulin), it starts burning fat rapidly. That process creates acids called ketones, which build up in the blood and can become life-threatening. Signs of DKA include extreme fatigue, difficulty breathing, fruity-smelling breath, abdominal pain, nausea, and fainting. This is a medical emergency. Some people don’t know they have type 1 diabetes until they end up in the hospital with DKA.
Type 2 diabetes, on the other hand, is often caught during routine bloodwork before symptoms become severe. That’s one reason screening matters so much, even if you feel fine.
Risk Factors That Should Prompt Testing
You don’t need symptoms to be at risk. Several factors make type 2 diabetes significantly more likely:
- Weight: carrying excess weight, especially around the midsection
- Age: being 45 or older
- Family history: having a parent or sibling with type 2 diabetes
- Activity level: exercising fewer than three times a week
- Ethnicity: African American, Hispanic or Latino, American Indian, Alaska Native, and some Asian American and Pacific Islander populations face higher risk
- Pregnancy history: having had gestational diabetes or delivering a baby over 9 pounds
- Liver health: having non-alcoholic fatty liver disease
For type 1 diabetes, the risk factors are different. It typically develops in children, teens, and young adults, and having a parent or sibling with type 1 increases your chances. In the United States, White people are more likely to develop type 1 than African American or Hispanic populations.
If you check several boxes on the type 2 list, getting tested is worthwhile even if you feel perfectly healthy.
The Blood Tests Used to Diagnose Diabetes
A doctor will typically use one of three blood tests to check for diabetes. Each measures blood sugar in a different way, and the numbers fall into three categories: normal, prediabetes, and diabetes.
A1C Test
This test measures your average blood sugar over the past three months. No fasting required. The result comes back as a percentage: below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher means diabetes. Because it reflects a longer window, a single stressful day or skipped meal won’t throw off the number.
Fasting Blood Glucose Test
You’ll need to fast for at least 8 hours beforehand (water is fine). A reading below 100 mg/dL is normal. Between 100 and 125 mg/dL falls in the prediabetes range. A result of 126 mg/dL or higher points to diabetes.
Oral Glucose Tolerance Test
This one also requires fasting. Your blood is drawn once, then you drink a sugary liquid and wait two hours for a second draw. Below 140 mg/dL is normal, 140 to 199 mg/dL is prediabetes, and 200 mg/dL or higher indicates diabetes. This test is also used during pregnancy screening, though the protocol is slightly different for pregnant patients.
If your first test comes back high, your doctor will usually order a second test to confirm the diagnosis. One elevated reading alone typically isn’t enough for a definitive answer. The exception is when you already have clear symptoms of diabetes and a random blood glucose reading of 200 mg/dL or higher, which can be taken at any time without fasting.
Can a Home Glucose Monitor Tell You?
Over-the-counter glucose monitors, the kind people with diabetes use to check their blood sugar daily, can give you a rough snapshot. But they aren’t designed for diagnosis. These devices are considered accurate if they land within 15% of a lab reading, which is a wide enough margin to blur the line between prediabetes and normal, or between prediabetes and diabetes.
Accuracy also drops if you’re dehydrated, have anemia, or test from a site other than your fingertip when blood sugar is changing rapidly. A home monitor showing a high number is a reasonable reason to schedule lab work, but a normal reading doesn’t rule anything out. Lab-grade blood tests remain the standard for diagnosis.
What Happens After a Diagnosis
The standard blood tests can confirm diabetes but can’t tell you which type you have. If your doctor suspects type 1, they’ll look for specific autoantibodies in your blood. These are proteins your immune system produces when it mistakenly attacks the cells in your pancreas that make insulin. Finding these antibodies confirms type 1. In rare cases, genetic testing may be used to identify monogenic diabetes, a less common form caused by a single gene mutation.
For most adults diagnosed with type 2, the next steps focus on lifestyle changes and monitoring. Prediabetes, in particular, is a window where the condition can often be slowed or reversed through changes in diet, physical activity, and weight. That’s why catching it early matters so much, and why testing is valuable even when you feel fine.