Diabetes: types, tests, symptoms and warning signs

Medical disclaimer: This page is general health information for education only. It is not medical advice and is not a substitute for diagnosis or treatment by a qualified health professional. It has not been reviewed by a clinician. In an emergency, call 911 or your local emergency number.

A new diabetes or prediabetes diagnosis can bring a lot of new words at once. This page explains what diabetes is, the main types, how doctors diagnose it, and which warning signs need emergency care. It is part of our plain-language guide to health conditions.

What is diabetes?

Diabetes is a disease that occurs when your blood glucose, also called blood sugar, is too high. NIDDK explains how diabetes affects blood glucose.

Glucose is your body’s main source of energy. Insulin is a hormone made by the pancreas. It helps glucose move from your blood into your cells. With diabetes, your body makes too little insulin, makes none, or does not use insulin properly. Glucose then stays in your blood instead of reaching your cells.

Diabetes is common. More than 40 million Americans have diabetes, according to the CDC. More than 1 in 4 adults with diabetes do not know they have it. CDC diabetes basics and statistics.

This page gives general information only. It cannot tell you which type you have or what treatment is right for you.

Types of diabetes and prediabetes

The most common types of diabetes are type 1, type 2, and gestational diabetes. Prediabetes is a related condition that comes before type 2.

• Type 1 diabetes: The immune system attacks and destroys the pancreas cells that make insulin. The body then makes little or no insulin. People with type 1 diabetes need to take insulin every day.
• Type 2 diabetes: The body does not use insulin properly, a problem called insulin resistance. Type 2 is the most common type. About 90% to 95% of diabetes cases are type 2.
• Gestational diabetes: This type develops during pregnancy in people who did not already have diabetes. It usually goes away after the baby is born. It raises the chance of type 2 diabetes later in life.
• Prediabetes: Blood glucose is higher than normal but not high enough for a type 2 diagnosis. Prediabetes raises your risk of type 2 diabetes and heart disease.

These type descriptions come from NIDDK’s overview of diabetes types. The CDC reports that more than 2 in 5 U.S. adults have prediabetes. About 8 in 10 people with prediabetes do not know they have it.

Rarer forms of diabetes exist, such as monogenic diabetes, and this list does not cover them. Standard blood tests confirm diabetes but cannot show which type you have. Doctors may use other tests, such as autoantibody tests, to tell type 1 from type 2.

How diabetes is diagnosed

Doctors diagnose diabetes and prediabetes with blood tests that show whether your blood glucose is higher than a healthy range.

• A1C test: Shows your average blood glucose over the last 3 months. You can eat and drink before this test.
• Fasting plasma glucose (FPG) test: Measures blood glucose after you fast for at least 8 hours.
• Oral glucose tolerance test (OGTT): Measures blood glucose 2 hours after you drink a sugary liquid.
• Random plasma glucose test: Can be done at any time when you have symptoms of diabetes.

These cutoffs come from NIDDK’s guide to diabetes tests and diagnosis, based on American Diabetes Association standards. Usually, your doctor will use a second test to confirm diabetes.

These cutoffs do not apply during pregnancy, where some tests use different values. A home blood glucose meter cannot diagnose diabetes. Certain hemoglobin variants can make A1C results less reliable for some people.

Common symptoms of diabetes

Common diabetes symptoms include increased urination, strong thirst, hunger after eating, blurred vision, fatigue, and sores that do not heal.

• Increased urination
• Feeling very thirsty
• Feeling very hungry, even after you have eaten
• Blurred vision
• Fatigue
• Sores that do not heal
• Frequent infections, such as urinary tract, skin, or yeast infections

This list comes from NIDDK’s page on diabetes symptoms and causes. Type 1 symptoms usually develop quickly, over a few days or weeks. People with type 1 may also lose weight without trying.

Type 2 symptoms can develop slowly, over several years. Many people with type 2 diabetes have no symptoms at all. Most people with gestational diabetes also have no symptoms.

Having no symptoms does not rule out diabetes. Only a blood test can confirm or rule out the diagnosis.

Why ongoing diabetes care matters

Over time, high blood glucose can damage your heart, kidneys, feet, and eyes. Managing diabetes can lower your chance of these problems.

The CDC calls diabetes a chronic, or long-lasting, condition. There isn’t a cure yet for diabetes. Diabetes is the No. 1 cause of kidney failure, lower-limb amputations, and adult blindness. CDC on diabetes complications.

Diabetes can also damage blood vessels and lead to heart disease and stroke. NIDDK notes that managing blood glucose, blood pressure, and cholesterol can help prevent future health problems. NIDDK also recommends a dilated eye exam at least once a year and a foot check at each care visit. NIDDK: Preventing diabetes problems.

Prediabetes is not a diagnosis to ignore. People with prediabetes have a high chance of developing type 2 diabetes within 5 to 10 years. In a large NIH study, losing 5% to 7% of starting weight lowered the chance of type 2 diabetes in high-risk people. NIDDK: Prediabetes and insulin resistance.

This section does not describe a treatment plan. Your care plan, including any medicines, should come from your own health care team.

Urgent warning signs: when to call 911

Diabetic ketoacidosis (DKA) is a medical emergency. It happens when the body lacks enough insulin and starts burning fat for energy.

DKA usually affects people with type 1 diabetes, but people with type 2 can also develop it. Sometimes DKA is the first sign that someone has type 1 diabetes. The CDC says to go to the emergency room or call 911 right away if:

• Your blood sugar stays at 300 mg/dL or above
• Your breath smells fruity
• You are vomiting and cannot keep food or drinks down
• You are having trouble breathing
• You have multiple signs and symptoms of DKA

These signs come from the CDC page on diabetic ketoacidosis. Other DKA symptoms include fast, deep breathing, dry skin and mouth, a flushed face, headache, stomach pain, and feeling very tired.

This list does not cover every diabetes emergency. Low blood sugar, called hypoglycemia, can also become severe. Ask your care team what to do if your blood sugar drops too low. Our first aid basics page explains how to prepare for emergencies.

Questions to bring to your appointment

A written list of questions can help you use your visit well. Our guide on how to prepare for a doctor’s appointment has more tips. These questions are a starting point and do not replace advice from your care team.

• Which type of diabetes do I have, and how was that confirmed?
• What were my test results, and which test was used?
• What blood glucose and A1C targets are right for me?
• How often should I have eye, foot, kidney, and dental checks?
• What warning signs mean I should call you, and which mean I should call 911?
• If I have prediabetes, is a lifestyle change program right for me?