A number of tests can help diagnose type 1 diabetes, including an at-home fingerstick or hemoglobin A1C test. Other autoantibody testing can be done if there’s a parent or sibling with this autoimmune condition.

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The onset of type 1 diabetes (T1D) can happen very suddenly. While there is no consensus as to a single, specific cause of this autoimmune condition, diagnosing it quickly is crucial and can be lifesaving.

Get tested for diabetes if you’re experiencing any diabetes symptoms, including:

  • extreme thirst
  • weight loss
  • frequent urination
  • blurry vision
  • fruity-smelling breath

To understand how doctors diagnose T1D, it’s important to understand what this autoimmune condition is and why that matters for those who may be experiencing symptoms.

T1D is an autoimmune disease where the insulin-producing cells in the pancreas are destroyed and cannot make insulin.

Every person needs insulin to live. It’s a hormone that helps your body use sugar (glucose) for energy. That glucose comes from the food you eat. Insulin allows glucose to pass from your blood into your body’s cells.

People with T1D need to take insulin. They can do this by injection, through an inhaled form, or by using a small insulin pump device they wear on their body.

Type 1 diabetes can happen at any age

Before the 1990s, T1D was often referred to as “juvenile diabetes” because it was once seen as a condition usually diagnosed in childhood.

However, this autoimmune condition can develop at any age. Latent autoimmune diabetes in adults (LADA) is sometimes known as type 1.5 diabetes.

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Symptoms of T1D may be mistaken for flu-like symptoms, especially in children and teenagers. Some of the most common telltale symptoms of T1D include:

  • extreme thirst
  • rapid, unintentional weight loss
  • increased hunger
  • frequent urination
  • fruity-smelling breath
  • fatigue
  • blurry vision

These symptoms can occur suddenly. They are often the reason T1D is diagnosed: People with high blood sugars and diabetic ketoacidosis (DKA) go to the emergency room where medical professionals make the diagnosis.

Getting tested for diabetes is easy. It can be done with a blood test either at home or in a doctor’s office.

In the case of an emergency situation, your blood sugar will be tested upon your arrival at a hospital’s emergency department.

The methods used to diagnose T1D are often similar to how other types of diabetes are diagnosed. The specific diagnostic tests that can be used for T1D are the following:

Fingerstick blood test

Checking your blood sugar with a fingerstick is a simple test that can be done at home or at a doctor’s office.

For at-home testing, you can buy a glucose meter at your local pharmacy. You take the device home and check your blood sugar with a finger poke. This is sometimes referred to by medical professionals as a “random glucose plasma test.”

For diagnosing T1D, medical guidelines state the following results for people with this condition:

  • Fasting blood sugar (no eating or drinking except water for 8-plus hours): 126 mg/dL or above
  • Random plasma test, at least 1 to 2 hours after eating or drinking: 200 mg/dL or above
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Depending on the specific result and other symptoms, a medical professional will follow up a fingerstick test with a more advanced test known as the hemoglobin A1C test.

Hemoglobin A1c

An A1C blood test measures your average blood sugar level over the previous 3 months. This can show doctors whether your blood sugars have been high for quite some time.

The American Diabetes Association has established the following A1C guidelines for using the test as part of a diabetes diagnosis:

  • less than 5.7% indicates no diabetes
  • 5.7–6.4% indicates prediabetes
  • greater than 6.5% indicates diabetes
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Your pancreas needs what’s known as the enzyme glutamic acid decarboxylase (GAD) to function normally. Antibodies, or the proteins that your immune system uses to attack viruses or bacteria, that target this particular enzyme are called GAD antibodies.

Sometimes, the immune system makes autoantibodies, which might mistakenly attack normal cells that aren’t harmful. When that happens, it causes an autoimmune disorder, such as T1D.

Because T1D is an autoimmune disease, a medical professional can perform an autoantibody test to help determine whether you’re living with this condition.

Additionally, if you have immediate family members — especially parents or siblings — already living with T1D, then you can get tested for the genetic markers for the condition.

These tests measure the antibody response to insulin, the islet cells in the pancreas, or GAD. The antibodies associated with T1D include:

  • islet cell cytoplasmic autoantibodies (ICAs)
  • insulinoma-associated-2 autoantibodies (IA-2As)
  • insulin autoantibodies (IAAs), which are more common in children than adults
  • zinc transporter 8 autoantibody (ZnT8A)
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These autoantibody tests are done through a simple blood test at a doctor’s office or lab. A medical professional will take blood from a vein in your arm and send it to another laboratory for analysis.

If you have any of the autoantibodies, you have a higher risk of developing T1D. For people who already have a diagnosis of another form of diabetes, it could help determine whether you’ve been misdiagnosed and actually have T1D.

As to developing T1D later on, a high level of antibody response indicates a person has a higher likelihoodof developing the condition in the future. However, there’s no guaranteed diagnosis.

Type 1 diabetes (T1D) is an autoimmune condition that can develop at any age. T1D symptoms often include increased hunger and thirst, unexplained weight loss, frequent urination, fruity-smelling breath, and flu-like symptoms. Tests that are typically used to help diagnose T1D include a fingerstick blood test at home or in a doctor’s office as well as a hemoglobin A1C test. This test measures your average blood sugar over the past few months.

You can also have more advanced autoantibody testing to determine whether you’re living with T1D or another type of diabetes, or if there’s any increased likelihood based on an immediate family member’s diabetes diagnosis.