March 6, 2026

How Do You Know If You Have Diabetes? You usually know you might have diabetes if you notice common warning signs such as frequent urination, unusual thirst, increased hunger, unexplained weight loss, fatigue, blurry vision, slow-healing sores, or frequent infections. The only way to know for sure is with a medical blood test, such as an A1C, fasting plasma glucose, oral glucose tolerance test, or random plasma glucose test when symptoms are present. This question matters because diabetes can be easy to miss. CDC says 40.1 million people in the United States have diabetes, and more than 1 in 4 adults with diabetes do not know they have it. The tricky part is that diabetes does not always feel dramatic at first. Type 2 diabetes can develop slowly over years and sometimes causes no obvious symptoms, while type 1 diabetes often appears faster and can become dangerous quickly. What are the most common signs and symptoms of diabetes? The most common signs of diabetes are changes caused by high blood sugar, and they often show up as thirst, frequent urination, hunger, tiredness, blurred vision, infections, and sometimes weight loss. These are the symptoms most people should know first. Common warning signs include the following. Frequent urination Feeling very thirsty Feeling hungrier than usual Unexplained weight loss Fatigue or low energy Blurry vision Frequent urinary tract infections or yeast infections Slow-healing sores Skin or other frequent infections These symptoms happen because glucose builds up in the blood instead of being used properly by the body. In type 2 diabetes, this is often linked to insulin resistance, which means the body does not respond to insulin normally. How are type 1 and type 2 diabetes symptoms different? Type 1 diabetes usually appears faster, while type 2 diabetes often develops more slowly and can go unnoticed for a long time. That difference in speed is one of the most useful clues. Type 1 diabetes symptoms may appear over days to weeks and can be severe. NIDDK says many people do not realize they have type 1 diabetes until symptoms start, and some people first present with diabetic ketoacidosis, or DKA. Type 2 diabetes symptoms often develop over several years. Many people with type 2 diabetes have no symptoms at all, or the symptoms are so mild that they are easy to miss. Can you have diabetes without noticing symptoms? Yes, you can have diabetes without noticing symptoms, especially type 2 diabetes and prediabetes. That is one reason diabetes is often found during routine testing rather than because a person feels obviously ill. CDC says type 2 diabetes symptoms can develop over several years and may not be noticeable at all. NIDDK also notes that many people with type 2 diabetes have no symptoms or only very mild symptoms. Prediabetes can also be silent. CDC reports that 115.2 million American adults have prediabetes, and 8 in 10 do not know it. That means the absence of symptoms does not rule out a blood sugar problem. If you have risk factors, testing matters even if you feel normal. What tests are used to diagnose diabetes? Doctors diagnose diabetes with blood tests, not by symptoms alone. The main tests are the A1C test, fasting plasma glucose test, oral glucose tolerance test, and random plasma glucose test when symptoms are present. Here is what each test does. A1C test: Shows average blood glucose over about the last 3 months. Fasting plasma glucose (FPG): Measures blood sugar after at least 8 hours of fasting. Oral glucose tolerance test (OGTT): Measures how your body handles glucose before and after a sugary drink. Random plasma glucose: Can help diagnose diabetes right away if classic symptoms are present. During pregnancy, doctors may first use a glucose challenge test, then an oral glucose tolerance test if the screening result is high. CDC says gestational diabetes screening usually happens between 24 and 28 weeks of pregnancy. A diagnosis usually needs confirmation. The American Diabetes Association says diabetes tests often need to be repeated on a second day, unless blood sugar is very high or a person has classic symptoms plus one positive test. There are also special situations. NIDDK notes that A1C may be less reliable in some people, including those in later pregnancy or those with certain blood conditions or hemoglobin variants. What blood sugar levels mean diabetes or prediabetes? Standard diagnostic cutoffs help doctors separate normal blood sugar, prediabetes, and diabetes. These are the most commonly used thresholds from NIDDK, citing ADA criteria. Test Normal Prediabetes Diabetes A1C Below 5.7% 5.7% to 6.4% 6.5% or above Fasting plasma glucose 99 mg/dL or below 100 to 125 mg/dL 126 mg/dL or above 2-hour oral glucose tolerance test 139 mg/dL or below 140 to 199 mg/dL 200 mg/dL or above Random plasma glucose — — 200 mg/dL or above with symptoms These numbers matter because they show that diabetes is not diagnosed by “feeling bad” alone. A person can feel unwell and still need formal testing, or feel normal and still meet lab criteria for diabetes or prediabetes. Who should get tested for diabetes? People should ask about diabetes testing if they have symptoms, are older, or have risk factors such as being overweight, having a family history, prediabetes, past gestational diabetes, or low physical activity. Screening matters because diabetes and prediabetes are often silent. NIDDK says adults are more likely to develop type 2 diabetes if they are overweight or have obesity, are age 35 or older, have a family history of diabetes, have prediabetes, have had gestational diabetes, or are not physically active. NIDDK also lists higher risk in several racial and ethnic groups, including African American, American Indian, Asian American, Hispanic/Latino, and Pacific Islander populations. CDC adds a practical screening message for A1C testing: get an A1C test if you are over age 45, or if you are younger but have overweight plus another risk factor for prediabetes or type 2 diabetes. For children, NIDDK says health professionals begin testing