Talk to your doctor or pharmacist before taking any supplement if you have diabetes or take diabetes medication. Never stop or change your medication on your own. Get urgent care right away for emergency symptoms such as confusion, trouble breathing, fainting, repeated vomiting or a seizure.
High blood sugar often does not announce itself. Many people with prediabetes or type 2 diabetes feel fine, and others notice symptoms so gradually that they put them down to stress or age. This guide covers the common symptoms, the tests doctors use and what the numbers mean, the signs that mean an emergency, and what to do at each level. It is meant to help you decide when to get tested, not to let you diagnose yourself.
Quick triage: green, yellow, red
Green: schedule a routine check
No symptoms, but you are overweight, have a close relative with type 2 diabetes, had gestational diabetes, or have not been tested in years. Ask your clinician whether and when to test.
Yellow: call this week
More thirst and urination than usual, constant hunger, blurred vision, tiredness, sores that heal slowly, frequent infections, or numbness and tingling in the hands or feet.
Red: emergency care now
Fruity-smelling breath, trouble breathing, belly pain with vomiting, fainting, confusion, a seizure, or chest pain. Call 911 or your local emergency number.
Symptoms of high blood sugar
NIDDK lists the common symptoms of diabetes, which apply to any type:
- Urinating more often than usual
- Feeling very thirsty
- Feeling very hungry, even after eating
- Blurred vision
- Fatigue
- Sores that do not heal
- Frequent infections, such as urinary tract, skin or yeast infections
Type 1 diabetes may also cause unexplained weight loss. When diabetes has been present for years, people may first notice signs of damage rather than thirst: pain, numbness or tingling in the feet or hands, sexual problems, chest pain or vision loss. These are reasons to be seen promptly. Source: NIDDK, Symptoms and causes of diabetes.
These symptoms have many other causes. Having one does not mean you have diabetes, and having none does not mean you do not.
Type 1, type 2, prediabetes and pregnancy
Type 1
Symptoms usually develop quickly, over days or weeks. It is often diagnosed in children and young adults but can start at any age. Sometimes the first sign is diabetic ketoacidosis (DKA).
Type 2
Symptoms can develop slowly over several years. Many people have no symptoms or very mild ones. People may find out when they develop a related health problem.
Prediabetes
Blood sugar is higher than normal but not high enough for diabetes. The American Diabetes Association says there are no clear symptoms, that over 115 million Americans have prediabetes, and that 80 percent of them do not know.
Gestational
Develops during pregnancy. NIDDK says most pregnant women should be tested, and the CDC says testing usually happens at 24 to 28 weeks.
Sources: ADA on prediabetes; CDC, Diabetes testing.
The tests and what the ranges mean
Diagnosis is made by blood tests in a clinic or lab. Four are common. The ranges below follow the American Diabetes Association criteria as shown by NIDDK.
| Test | How it works | Normal | Prediabetes | Diabetes |
|---|---|---|---|---|
| A1C | Average blood sugar over the past 2 to 3 months. No fasting needed. | Below 5.7% | 5.7% to 6.4% | 6.5% or higher |
| Fasting plasma glucose | After at least 8 hours with nothing to eat or drink except water, usually in the morning. | 99 mg/dL or below | 100 to 125 mg/dL | 126 mg/dL or higher |
| Oral glucose tolerance test (OGTT) | Blood is taken, you drink a sugary liquid, and blood is tested again 2 hours later. | 139 mg/dL or below | 140 to 199 mg/dL | 200 mg/dL or higher |
| Random plasma glucose | Any time of day, used when symptoms are present. | Not applicable | Not applicable | 200 mg/dL or higher |
The ADA says each test usually needs to be repeated on a second day to confirm diabetes. If your blood glucose is very high, or you have classic symptoms plus one positive test, your doctor may not need a second test. If you have prediabetes, you should be checked for type 2 diabetes every one to two years. Sources: ADA, Diagnosis; NIDDK, Tests and diagnosis; MedlinePlus on the A1C test.
Home meters and one-off readings
A finger-stick meter is useful for people already diagnosed. A single high reading after a big meal does not make a diagnosis, and a single normal reading does not rule one out. If a reading worries you, take it to a clinician and ask for a lab test.
Emergency signs
Diabetic ketoacidosis (DKA)
NIDDK describes DKA as a medical emergency that needs treatment right away. It mostly affects people with type 1 diabetes but can occur in type 2. Its signs include feeling very tired, trouble breathing, fruity-smelling breath, fainting from dehydration, and pain in the abdomen with nausea or vomiting. The body is short of insulin and begins to burn fat, which makes substances called ketones.
Other warning signs
MedlinePlus says to call 911 or the local emergency number for chest pain or pressure, fainting, confusion or unconsciousness, seizure, shortness of breath, or red painful skin spreading quickly, because these can quickly turn into emergencies including hypoglycemic or hyperglycemic coma. Sources: NIDDK; MedlinePlus, Type 2 diabetes.
Low blood sugar looks different
Shakiness, sweating, hunger, dizziness and a racing heartbeat can be a sign of too-low blood sugar, mostly in people who take insulin or some diabetes pills. It needs different treatment from high blood sugar. See our side effects and interactions guide and the NIDDK page on low blood glucose.
Prepare for the appointment
- Write down symptoms, when they started, and whether they come and go.
- List every medicine, vitamin and supplement you take, with doses. Photograph supplement labels.
- Note family history of diabetes, heart disease and gestational diabetes.
- Ask if you need to fast and for how many hours. Fasting means water only.
- Ask which test will be done, when results arrive, and what number would lead to a repeat test.
- Ask what the plan would be if the result falls in the prediabetes range.
- Bring a list of questions, such as how often to retest and whether a prevention program fits.
After a result: what next
- Normal result. Ask when to retest based on your risk factors. Keep healthy habits (see the lifestyle guide).
- Prediabetes. The ADA says for some people, early treatment and moderate lifestyle changes can return blood glucose to the normal range. NIDDK says losing 5 to 7 percent of body weight and being active most days may prevent or delay type 2 diabetes. The CDC points to a lifestyle change program for people with confirmed prediabetes.
- Diabetes. Your clinician will confirm the type and agree a plan that may include medicine, food planning, activity and monitoring. NIDDK notes that taking insulin or other diabetes medicines is often part of treatment, along with healthy choices.
- If someone offers a supplement as a fix. Treat that as a topic for your clinician, not a replacement for the plan. Our evidence review explains why.
Three myths worth dropping
"No symptoms, so I am fine"
The ADA says 80 percent of Americans with prediabetes do not know they have it, and NCCIH notes about one in four adults with diabetes does not know. Testing is the only way to find out.
"My meter can diagnose me"
NIDDK says not to try to diagnose yourself. Diagnosis rests on lab tests, often repeated on a second day.
"A supplement can fix the number"
The FTC, citing the ADA, says there is no clear proof that any supplement treats diabetes or high blood sugar, and that relying on one can delay proven care.
Why finding it early matters
NIDDK explains that too much glucose in the blood over time can cause health problems such as heart disease, nerve damage, eye problems and kidney disease. It also notes that delaying type 2 diabetes by even a few years benefits your health. That is the practical reason to test even when you feel well, and to act on a prediabetes result rather than waiting to see what happens.
A worked example of reading two results
Suppose a lab reports an A1C of 6.0 percent and a fasting glucose of 108 mg/dL. Both fall in the prediabetes ranges in the table above. That would typically lead to a conversation about lifestyle changes, a prevention program and a repeat test within a year or two, and not to a diagnosis of diabetes. If instead the A1C was 6.8 percent and a repeat test on another day was also 6.5 percent or higher, that meets the diabetes criteria. The point of the example is to show how the ranges work. Your own results need your own clinician.
Who should be tested
NIDDK says anyone with symptoms should be tested, and some people with no symptoms but risk factors for type 2 diabetes also need testing. Risk factors include being overweight, having a parent, brother or sister with type 2 diabetes, and having had gestational diabetes. Most pregnant women are tested for gestational diabetes. Medicare may cover tests for people with certain risk factors, so ask your insurer about coverage.
Sources
- NIDDK, Symptoms and causes of diabetes.
- NIDDK, Diabetes tests and diagnosis.
- American Diabetes Association, Diagnosis; Prediabetes.
- CDC, Diabetes testing (May 2024).
- MedlinePlus, Type 2 diabetes; Hemoglobin A1C test.
- NIDDK, Low blood glucose (hypoglycemia).
- NIDDK, Preventing type 2 diabetes.
Frequently asked questions
What are the symptoms of high blood sugar?
NIDDK lists increased urination, intense thirst, hunger even after eating, blurred vision, fatigue, sores that do not heal and frequent infections. Many people with type 2 diabetes have mild symptoms or none.
What is a normal A1C?
The American Diabetes Association lists an A1C below 5.7 percent as normal, 5.7 to 6.4 percent as prediabetes and 6.5 percent or higher as diabetes.
What fasting glucose is considered prediabetes?
A fasting plasma glucose of 100 to 125 mg/dL is in the prediabetes range, and 126 mg/dL or higher points to diabetes. A clinician confirms the result.
Does prediabetes have symptoms?
Usually not. The ADA says there are no clear symptoms of prediabetes, so testing is how people find out.
When is high blood sugar an emergency?
Fruity-smelling breath, trouble breathing, belly pain with vomiting, confusion, fainting or a seizure need emergency care. Call 911 or your local emergency number.