High blood sugar often announces itself through a handful of recognizable symptoms, most notably increased thirst, frequent urination, and unusual fatigue. But it can also climb quietly, especially in the early stages. Knowing both the physical signs and the numbers that matter gives you the clearest picture of where you stand.
The Earliest Symptoms to Watch For
The most common early signs of high blood sugar are frequent urination, increased thirst, and persistent tiredness. These three tend to appear together and reinforce each other. When glucose builds up in your blood beyond what your kidneys can reabsorb, the excess spills into your urine and pulls extra water along with it. That’s why you urinate more often, which dehydrates you, which makes you thirsty, which can leave you feeling drained.
Other early signs include:
- Blurred vision, caused by fluid shifts in the lens of the eye
- Increased hunger, even shortly after eating
- Unexplained weight loss, particularly in type 1 diabetes
- Irritability or mood changes
- Frequent yeast infections or UTIs, since elevated glucose creates a favorable environment for bacteria and yeast
These symptoms can develop gradually over weeks or months, which is why many people attribute them to stress, aging, or poor sleep before considering blood sugar as the cause. If you’re experiencing several of them at once, that pattern is more telling than any single symptom on its own.
Signs That Have Been Building for Months
When blood sugar stays elevated over a longer period, it starts to damage smaller blood vessels and nerves. The signs of this damage are subtler but important to recognize because they suggest the problem isn’t new.
Tingling, numbness, or a “pins and needles” sensation in your hands or feet is one of the more common indicators of nerve damage from prolonged high glucose. You might also notice that cuts, scrapes, or sores take noticeably longer to heal than they used to. Reduced blood flow and nerve function slow the body’s repair process and increase infection risk, particularly in the feet and lower legs.
Vision changes can also worsen over time. Short-term blurriness from fluid shifts is one thing, but sustained high blood sugar can damage the tiny blood vessels in the retina, leading to swelling that distorts your central vision. It also raises the risk of cataracts, where the lens of the eye becomes cloudy.
What the Numbers Actually Mean
Symptoms give you clues, but a blood test gives you a definitive answer. There are a few key numbers to understand.
The A1C test measures your average blood sugar over the past two to three months. It’s reported as a percentage:
- Below 5.7%: normal
- 5.7% to 6.4%: prediabetes
- 6.5% or above: diabetes
If you already have diabetes and are monitoring at home with a glucose meter, the American Diabetes Association recommends these targets for most nonpregnant adults: 80 to 130 mg/dL before a meal, and less than 180 mg/dL one to two hours after starting a meal. An A1C below 7% (equivalent to an average of about 154 mg/dL) is the general goal.
A single reading above these ranges doesn’t necessarily mean something is wrong. Blood sugar fluctuates throughout the day based on food, activity, stress, and sleep. A pattern of consistently elevated readings is what matters.
How to Test at Home
The most common home testing method is a finger-stick glucose meter. You prick your finger, place a drop of blood on a test strip, and the meter displays your blood sugar level within seconds. It remains the most reliable way to get an accurate reading at a specific moment in time.
Continuous glucose monitors (CGMs) are a newer option. A small sensor sits just under your skin and measures glucose every few minutes, sending readings to your phone or a small receiver. CGMs are especially useful for spotting trends and alerting you when levels climb too high or drop too low. The sensors need replacing every 10 to 15 days depending on the brand, and in rare cases you may still need a finger-stick meter to confirm a result.
When you test matters almost as much as how you test. For people taking insulin, the most informative times are before meals, before bed, and before and after exercise. If you take a long-acting insulin only, testing before breakfast and occasionally before dinner or at bedtime may be enough. You should also test more frequently when you’re sick, about to drive a long distance, or making significant changes to your diet or activity level.
Urine Tests for Ketones
Urine test strips can detect ketones, which are chemicals your body produces when it burns fat for energy instead of glucose. Small amounts of ketones are normal during fasting or intense exercise, but high ketone levels alongside high blood sugar can signal a dangerous condition called diabetic ketoacidosis, or DKA.
DKA is most common in type 1 diabetes but can also occur in type 2. Home urine test strips are inexpensive and worth keeping on hand if your doctor recommends them. They’re particularly useful when you’re feeling unwell or notice your blood sugar readings climbing above your usual range.
When High Blood Sugar Becomes an Emergency
Most of the time, elevated blood sugar is something you manage gradually with your care team. But certain symptoms call for immediate action. If your blood sugar stays at or above 300 mg/dL, you experience nausea and vomiting you can’t control, your breath develops a fruity smell, or you have trouble breathing or feel confused, these are signs of DKA or a related emergency called hyperosmolar hyperglycemic state.
Fruity-smelling breath is one of the more distinctive warning signs. It comes from the buildup of ketones and is not something that happens at mildly elevated blood sugar levels. Other red flags include fast, deep breathing, severe abdominal pain, muscle stiffness, and extreme fatigue that goes well beyond ordinary tiredness. Any combination of these symptoms warrants a call to 911 or a trip to the emergency room.