What are the signs of high blood sugar?
Strong thirst, peeing a lot, blurry vision, tiredness and weight loss you didn’t try for, plus infections that keep coming back and cuts that heal slowly. Prediabetes usually has none of these, which is why 8 in 10 people who have it don’t know. A blood test is the only way to find out early.
What we’d do
Don’t wait for symptoms. By the time high blood sugar makes you thirsty, it’s usually past the prediabetes stage. Get a lab A1c and fasting glucose every 3 years from 35, or now if you carry extra weight and have a risk factor. If you have the signs below, book a lab test this week, and call your doctor today if they’re strong or a meter shows 200 or more.
Why people wait for a sign
Most health problems announce themselves, so it’s natural to assume you’d feel high blood sugar. You usually don’t, not for years. Type 2 diabetes symptoms often take several years to develop, and some people never notice any (CDC). The National Institute of Diabetes and Digestive and Kidney Diseases says many people with type 2 have no symptoms, or symptoms so mild they don’t notice them. Of the 40.1 million Americans with diabetes, 27.6% of adults with it haven’t been diagnosed.
The signs
| Sign | What’s going on |
|---|---|
| Strong thirst | your body is losing extra water through your urine |
| Peeing a lot, getting up at night to pee | your kidneys are spilling sugar, and water goes with it |
| Blurry vision | one of the classic signs on the CDC and NIDDK lists |
| Tiredness | sugar stays in your blood instead of getting into your cells |
| Weight loss you didn’t try for | your body can’t use its sugar for fuel |
| Hunger, even after eating | the same reason |
| Infections that keep coming back, like urinary or yeast infections | over time, high sugar weakens the immune system |
| Cuts and sores that heal slowly, numb or tingling feet, dark skin patches on the neck or armpits | listed by the CDC as signs of type 2 |
The symptom list is the CDC’s and NIDDK’s. Normally your kidneys hold on to sugar and send it back into your blood, so there’s little or none in your urine (MedlinePlus). When blood sugar runs high enough, sugar ends up in the urine, and diabetes is the most common reason it does.
It’s like a bathtub. Your kidneys hold the water in until it reaches the overflow drain, and only then does it start running out.
Why prediabetes is silent
Prediabetes numbers are only a little above normal, usually too low to cause thirst or peeing. In the Whitehall II study of 6,538 British civil servants, insulin sensitivity fell steeply for 5 years before anyone got a diabetes diagnosis. More than 2 in 5 American adults, 115.2 million, have prediabetes now, and 8 in 10 of them don’t know it (CDC, 2026).
When to call
| You have | Do this |
|---|---|
| Any of the signs above, mild | book a lab A1c and fasting glucose this week |
| A blood sugar of 200 or more with strong thirst, peeing a lot, blurry vision or weight loss you didn’t try for | call your doctor today |
| Blood sugar staying at 300 or more, fruity breath, vomiting so you can’t keep fluids down, or hard breathing | go to the ER or call 911 |
A blood sugar of 200 or more with those symptoms counts as the diabetes range on its own, at any time of day (American Diabetes Association, 2026). The quiz scores your risk the way the CDC does, so you know whether to test now: could I have prediabetes?
9 sources
- CDC, Diabetes symptomscdc.gov
- National Institute of Diabetes and Digestive and Kidney Diseases, Symptoms and causes of diabetesniddk.nih.gov
- MedlinePlus, Glucose in urine test, US National Library of Medicinemedlineplus.gov
- CDC, Prediabetes: Could It Be You? (updated February 17, 2026)cdc.gov
- CDC, National Diabetes Statistics Report, at a glance (updated September 16, 2026)cdc.gov
- Tabák AG and others, Trajectories of glycaemia, insulin sensitivity, and insulin secretion before diagnosis of type 2 diabetes: an analysis from the Whitehall II study, Lancet, 2009pubmed.ncbi.nlm.nih.gov
- MedlinePlus, High blood sugar, US National Library of Medicinemedlineplus.gov
- CDC, Diabetic ketoacidosiscdc.gov
- American Diabetes Association, Standards of Care in Diabetes 2026, section 2, Diagnosis and Classification of Diabetespmc.ncbi.nlm.nih.gov
