How Is Type 1 Diabetes Diagnosed?

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Type 1 diabetes is a chronic autoimmune condition in which the pancreas makes very little or no insulin. Without insulin, the amount of glucose in the blood (or, blood sugar) builds up and the levels become too high. Over time, high blood sugar levels can damage the kidneys, eyes, heart, and nerves.

There are different ways to screen for and diagnose type 1 diabetes. Many of these tests involve measuring your body’s blood sugar levels. Testing is simple and you can expect your results to be available quickly. Blood sugar tests cannot be used to tell if you type 1 or type 2 diabetes.

Your treatment plan will be based on the type of diabetes, so it’s important for your healthcare provider (usually an endocrinologist, or a doctor who specializes in the glands of the endocrine system, including the pancreas) to identify the type. If they suspect type 1 diabetes, you may also undergo an autoantibody blood test and a ketone blood or urine test. Results from these two tests will help them confirm a type 1 diabetes diagnosis.

Medical History

Your healthcare provider will take your medical history to learn about your symptoms and when they started. Type 1 diabetes is diagnosed at any age, but symptoms tend to present between ages five to around puberty.

Type 1 diabetes tends to run in families, so your healthcare provider will want to know if you have a family history of the condition.

In addition to blood tests, symptoms are an important part of the type 1 diabetes diagnosis. Your healthcare provider will ask about your symptoms and when they first began. Most signs and symptoms of type 1 diabetes indicate high blood sugar levels (hyperglycemia). They include:

  • Excessive thirst (polydipsia)
  • Needing to urinate frequently (polyuria)
  • Feeling tired or fatigued
  • Losing weight without trying
  • Slowly healing wounds

Some people experience a delay in getting a type 1 diabetes diagnosis. As a result, the first symptoms they present with are signs of a diabetes complication called diabetic ketoacidosis (DKA). In addition to symptoms of high blood sugar, you may have DKA symptoms such as:

  • Fruity odor on your breath
  • Nausea, vomiting, or stomach pain
  • Rapid breathing 
  • Feeling sluggish
  • Trouble paying attention or feeling confused

DKA is a very serious complication, and can sometimes lead to a coma. It is a medical emergency, so seek care immediately to prevent long-lasting damage.

Glucose Blood Test

If your healthcare provider suspects diabetes based on your symptoms, they will have you take one or more blood tests to help confirm a diagnosis. There are different types of glucose blood tests and each serves a specific purpose. A glucose blood test requires a blood sample, usually taken as a blood drawn from a vein or a finger stick.

A1C Test

The A1C test (also known as hemoglobin A1C or HbA1c test) is commonly used to diagnose diabetes. Glucose is a type of sugar your body uses to make energy. When sugar enters the bloodstream, it attaches to the protein hemoglobin in red blood cells.

It is normal to have some sugar attached to hemoglobin. However, people with higher blood sugar levels have more sugar attached to hemoglobin.

An A1C test reveals what percentage of red blood cells have sugar-coated hemoglobin. Since red blood cells turn over every three months, an A1C test gives an average measure of glucose levels over the last 90 days. Results from testing are:

  • Normal (no diabetes): Less than 5.7%
  • Prediabetes: 5.7% to 6.4%
  • Diabetes: 6.5% or higher 

Fasting Blood Sugar Test

A fasting blood sugar test measures your blood sugar after an overnight fast (not eating). To ensure accurate results, you must not eat or drink eight hours before the test. Other names for this test include blood glucose test or fasting blood glucose.

The purpose of a fasting blood sugar test is to see if your blood sugar levels are within a healthy range. If needed, the test may be repeated to confirm a diabetes diagnosis. Results from testing are:

  • Normal (no diabetes): 99 milligrams per deciliter (mg/dL) or lower
  • Prediabetes: 100 to 125 mg/dL
  • Diabetes: 126 mg/dL or higher

Random Blood Sugar Test

A random blood sugar test measures your blood sugar at the time you’re tested. This blood test can be taken at any time. You do not need to fast (not eat) before having your blood drawn. A blood sugar level of 200 mg/dL or higher indicates a diabetes diagnosis.

Ketone Test

When our body can’t get the glucose it needs to make energy, the body begins to burn fat instead. The liver converts fat into energy at an extremely fast rate, producing ketones during the process. When ketones are released into the blood too quickly, it makes the blood acidic.

This condition is known as diabetic ketoacidosis. Diabetic ketoacidosis is most common in people living with type 1 diabetes. It can develop in people with type 2 diabetes but is less common and less severe.

A ketone test is done using a urine or blood sample. This test detects the levels of ketone bodies produced through ketoacidosis.

Autoantibody Testing

Glucose blood tests are used to confirm a diabetes diagnosis, but they aren’t helpful in identifying what type of diabetes you may have. Once your glucose test results indicate diabetes, your healthcare provider may order antibody testing that is specific to type 1 diabetes.

With type 1 diabetes, the immune system attacks and destroys healthy insulin-producing beta cells in the pancreas. As this is happening, the body produces pancreatic autoantibodies.

These antibodies are proteins created by our immune system. They indicate that the immune system has started to destroy beta cells. Pancreatic autoantibodies are present in type 1 diabetes, but not in type 2 diabetes.

Results from autoantibody and glucose tests, along with your symptoms, help your healthcare provider form a type 1 diabetes diagnosis.

A Quick Review

Identifying symptoms is an important first step when seeking a type 1 diabetes diagnosis. Symptoms of type 1 diabetes include excessive thirst, frequent urination, and losing weight without trying.

Based on these symptoms, your healthcare provider will order glucose blood tests such as A1C, fasting blood sugar, or random blood sugar. Repeat testing may be needed. 

Blood sugar tests do not indicate what type of diabetes a person is living with. Your healthcare provider may order additional tests that are specific to type 1 diabetes. This may include a ketone urine or blood test or an autoantibody test.  

If you notice symptoms of type 1 diabetes in yourself or your child, it’s a good idea to get tested. Keep a list of symptoms and share them with your healthcare provider. An early diagnosis can help you get started on a treatment plan that works best for you and your lifestyle.

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