The most common early signs of diabetes are increased thirst, frequent urination, and unexplained weight loss. But nearly 43% of adults with diabetes worldwide don’t know they have it, often because symptoms develop so gradually they’re easy to dismiss. Knowing what to look for, and when blood tests are warranted, can make a significant difference in catching the condition early.
The Classic Symptoms
Three symptoms show up most reliably across both type 1 and type 2 diabetes: excessive thirst, frequent urination, and weight loss you can’t explain. They’re all connected. When blood sugar climbs too high, your kidneys can’t reabsorb all the extra glucose, so it spills into your urine. That pulls water from your tissues along with it, which dehydrates you and makes you thirsty. Drinking more leads to urinating more, and the cycle continues. The calories lost through all that excreted sugar can also cause rapid, unintentional weight loss.
Other symptoms that frequently appear alongside these three include constant hunger (even after eating), blurry vision, fatigue that doesn’t improve with rest, and numbness or tingling in your hands or feet. Slow-healing cuts and frequent infections, particularly yeast infections or urinary tract infections, are also common because high blood sugar impairs the body’s ability to fight off bacteria and repair tissue.
How Type 1 and Type 2 Feel Different
Type 1 diabetes tends to announce itself loudly. Symptoms can appear within just a few weeks or months, and they’re often severe enough that something clearly feels wrong. It most commonly develops in children, teens, and young adults, though it can occur at any age. Because the immune system is actively destroying the cells that make insulin, blood sugar rises quickly and the body shifts into crisis mode faster.
Type 2 diabetes is the opposite. It develops over years, and many people have elevated blood sugar for a long time before they notice anything. The early symptoms, like feeling a little more tired or thirsty than usual, are easy to attribute to stress, aging, or not drinking enough water. This is a big reason so many cases go undiagnosed. In North America, roughly 29% of people with diabetes don’t know they have it. In lower-income countries, that figure can exceed 50 or even 70%.
Skin Changes Worth Noticing
Your skin can signal insulin resistance before a blood test ever does. A condition called acanthosis nigricans causes dark, velvety patches to appear in body creases, most commonly on the neck, armpits, or groin. It sometimes shows up on the hands, elbows, or knees. These patches are a direct sign of insulin resistance and can indicate prediabetes or type 2 diabetes, especially in people carrying extra weight. If you notice this kind of skin darkening, it’s worth getting your blood sugar checked even if you feel fine otherwise.
Eye Problems Can Be a Clue
High blood sugar damages the tiny blood vessels in your eyes over time, but the tricky part is that early diabetic eye changes usually cause no symptoms at all. By the time you notice blurry or wavy vision, dark floaters, trouble seeing colors, or flashes of light, some damage has already occurred. This is why routine eye exams can sometimes catch diabetes before other symptoms appear. If you experience sudden vision changes, especially spots, a dark shadow across part of your vision, or eye pain, those warrant urgent attention.
Emergency Signs That Need Immediate Care
Diabetic ketoacidosis, or DKA, happens when the body runs so low on insulin that it starts breaking down fat for fuel at a dangerous rate. This produces acids called ketones that build up in the blood. DKA is most common in type 1 diabetes but can occur in type 2 as well.
The warning signs escalate quickly: fast, deep breathing; dry skin and mouth; a flushed face; fruity-smelling breath; nausea and vomiting; and stomach pain. If your breath smells fruity, you’re vomiting and can’t keep anything down, or you’re having difficulty breathing, that’s an emergency. DKA can become life-threatening within hours if untreated.
The Blood Tests That Confirm It
Symptoms alone can’t diagnose diabetes. A blood test is required, and there are three main options your doctor may use.
The A1C test measures your average blood sugar over the past two to three months. It doesn’t require fasting. A result below 5.7% is normal, 5.7% to 6.4% falls in the prediabetes range, and 6.5% or above indicates diabetes.
The fasting blood sugar test measures your glucose after an overnight fast. Normal is 99 mg/dL or below, prediabetes is 100 to 125 mg/dL, and 126 mg/dL or above points to diabetes.
The glucose tolerance test involves drinking a sugary solution and having your blood drawn two hours later. A reading of 200 mg/dL or higher at the two-hour mark suggests diabetes.
Doctors typically confirm the diagnosis with a second test on a different day, unless symptoms are obvious and blood sugar is very high.
Prediabetes: The Window Before Diagnosis
Prediabetes means your blood sugar is elevated but hasn’t crossed the threshold for diabetes. The numbers fall between normal and diabetic on any of the tests above: an A1C of 5.7% to 6.4%, or a fasting glucose of 100 to 125 mg/dL. More than 1 in 3 American adults have prediabetes, and most of them don’t know it.
Prediabetes rarely causes noticeable symptoms, which is why screening matters, especially if you have risk factors like carrying extra weight, having a family history of diabetes, being over 45, or having a history of gestational diabetes. The encouraging part is that prediabetes is reversible. Losing even a modest amount of weight and increasing physical activity can bring blood sugar back to normal and significantly reduce the risk of progressing to type 2 diabetes.
Who Should Get Tested
If you’re experiencing increased thirst, frequent urination, unexplained weight loss, or persistent fatigue, testing is straightforward and can give you a clear answer. But you don’t need symptoms to justify a screening. Current guidelines recommend testing for adults who are overweight and have at least one additional risk factor, such as a sedentary lifestyle, a first-degree relative with diabetes, high blood pressure, or belonging to a higher-risk ethnic group (including African American, Hispanic, Native American, and Asian American populations). For people without risk factors, routine screening is generally recommended starting at age 35.
A simple fasting blood draw or A1C test is all it takes. Given that nearly 43% of people with diabetes globally are walking around undiagnosed, knowing your numbers is one of the most practical steps you can take.