High blood sugar often announces itself through a handful of recognizable symptoms: urinating more than usual, feeling unusually thirsty, and fatigue that doesn’t improve with rest. A fasting blood sugar above 126 mg/dL on two separate tests, or a random reading of 200 mg/dL or higher, puts you in the diabetes range. But here’s the tricky part: blood sugar can run high for years without causing any obvious symptoms at all, especially with type 2 diabetes. Knowing what to look for, and when to grab a glucose meter, can make a real difference.
The Most Common Symptoms
The classic signs of high blood sugar overlap between type 1 and type 2 diabetes. Frequent urination comes first for most people because your kidneys work overtime to flush excess glucose out through urine. That fluid loss triggers increased thirst, sometimes to the point where no amount of water feels like enough. You may also notice increased hunger, unexplained weight loss, blurry vision, irritability, and recurring urinary tract or yeast infections.
Type 2 diabetes symptoms tend to develop slowly over several years, and many people don’t notice anything wrong during that time. Type 1, by contrast, can progress from zero symptoms to severe illness in just a few weeks. Nausea, vomiting, and stomach pain are more common with type 1 and can signal a dangerous complication called diabetic ketoacidosis.
Signs You Can See on Your Body
Chronically elevated blood sugar leaves physical clues beyond the symptoms you feel. Dark, velvety patches of skin in the creases of your neck, armpits, or groin (a condition called acanthosis nigricans) are one of the most recognizable. These patches sometimes also appear on the hands, elbows, or knees. Cuts or sores that take unusually long to heal are another hallmark, along with numbness or tingling in the hands or feet.
Skin infections also become more frequent. Fungal infections like jock itch, athlete’s foot, and vaginal yeast infections thrive when blood sugar is elevated. Bacterial infections around the eyelids, hair follicles, and fingernails are common too. If you’re dealing with recurring infections that keep coming back despite treatment, high blood sugar may be the underlying reason.
When There Are No Symptoms at All
This is what makes high blood sugar dangerous. The World Health Organization notes that type 2 diabetes is frequently diagnosed years after it actually began, often only after complications have already developed. Many people walk around with elevated glucose and feel perfectly fine. The longer blood sugar stays high without being detected or treated, the worse the health outcomes tend to be. The only way to catch silent high blood sugar is through testing.
What the Numbers Mean
Blood sugar is measured in milligrams per deciliter (mg/dL). Here’s how the ranges break down for a fasting test, meaning you haven’t eaten for at least 8 hours:
- Normal: below 100 mg/dL
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or higher on two separate tests
After eating, blood sugar naturally rises. For people managing diabetes, the target is to stay below 180 mg/dL two hours after the start of a meal. Before meals, the goal is 80 to 130 mg/dL. A random blood sugar reading of 200 mg/dL or higher, at any time of day, suggests diabetes regardless of when you last ate.
Your doctor may also order an A1C test, which measures your average blood sugar over the past two to three months. An A1C between 5.7% and 6.4% falls in the prediabetes range. At 6.5% or higher, you’re in the diabetes range. This test is useful because it captures the bigger picture rather than a single snapshot.
How to Check at Home
A basic glucose meter from any pharmacy gives you a reading in seconds from a small finger prick. The most useful times to test are first thing in the morning before eating (your fasting level) and two hours after meals (to see how your body handles food). If you take insulin, you may need to test more frequently: before meals, before bed, and sometimes during the night.
Continuous glucose monitors are another option. These small sensors attach to your arm or abdomen and track your levels around the clock, sending data to your phone. They’re especially helpful for spotting patterns you’d miss with occasional finger pricks, like blood sugar spikes overnight or after specific foods.
Why Morning Blood Sugar Can Be High
If your fasting numbers are consistently elevated even though you ate well the night before, two things could be happening. The more common one is the dawn phenomenon: between roughly 3 and 8 a.m., your body releases hormones like cortisol and growth hormone that tell your liver to produce more glucose to help you wake up. In people with diabetes, there isn’t enough insulin to counteract that surge, so blood sugar is already high by the time you open your eyes.
Less commonly, the Somogyi effect can be responsible. This happens when blood sugar drops too low during the night, perhaps because you skipped dinner or took too much insulin. Your body overcompensates by dumping glucose into your bloodstream, and you wake up with a high reading. The distinction matters because the solutions are different. Checking your blood sugar around 2 or 3 a.m. for a few nights can help you figure out which pattern you’re dealing with.
When It Becomes an Emergency
Blood sugar above 250 mg/dL is a signal to start testing your urine for ketones using over-the-counter test strips. Ketones build up when your body can’t use glucose for energy and starts breaking down fat instead, and high levels can lead to diabetic ketoacidosis. You should check for ketones if your blood sugar is above 250 mg/dL when you wake up, or if two readings in a row come back above that level.
A positive ketone test at a moderate or high level warrants an immediate call to your healthcare provider. Blood sugar that stays at or above 300 mg/dL is an emergency room situation. Warning signs of ketoacidosis include fast, deep breathing, fruity-smelling breath, dry mouth, nausea and vomiting, stomach pain, and extreme fatigue. These symptoms can escalate quickly, especially in people with type 1 diabetes.
At the extreme end, blood sugar above 600 mg/dL can trigger a life-threatening condition called hyperosmolar syndrome, which causes severe dehydration and confusion. This is most common in older adults with type 2 diabetes and requires emergency treatment.