How Is Type 2 Diabetes Diagnosed?

Type 2 diabetes is diagnosed by testing your blood glucose (or blood sugar) levels.

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Lab professional with blood specimen for hemoglobin A1C test

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Type 2 diabetes is a chronic condition characterized by abnormal insulin processing in your body, causing high blood sugar levels. Diabetes affects more than 30 million Americans, and type 2 diabetes accounts for about 90% of diagnosed cases.

Insulin is a hormone produced by your pancreas. It is responsible for carrying blood sugar into your body's tissues to use for energy. If you have diabetes, your pancreas cannot produce insulin, or your cells do not respond to the insulin your pancreas creates. This results in increased blood sugar, which can lead to a number of health risks. These risks include cardiovascular disease, blindness, kidney failure, and limb amputation, among many others.

Type 2 diabetes is diagnosed by testing your blood glucose (or blood sugar) levels. These tests are usually done in a doctor’s office or clinical laboratories.

Getting a Diabetes Diagnosis

Type 2 diabetes and its initial stage, prediabetes, are diagnosed by measuring your blood sugar levels. Blood sugar levels are measured during your standard yearly physical with your healthcare provider or during checkups for another disease.

If your blood sugar levels are found to be higher than average, your healthcare provider will order several tests to confirm a diabetes diagnosis. The following are the typical tests that healthcare providers use to make a diabetes diagnosis.

A1C Test

An A1C test measures your average blood sugar for the past two to three months. The A1C test is also called a glycated hemoglobin, glycosylated hemoglobin, hemoglobin A1C, or HbA1C test.

This test measures how much of your blood cells are covered with sugar. When sugar enters the bloodstream, it grabs onto hemoglobin, the protein in your blood that carries oxygen. Though sugar attaching to hemoglobin is a normal biological process, a high amount of sugar-coated hemoglobin puts individuals at a high risk of developing prediabetes and diabetes.

An A1C test is reported as a percentage. Your healthcare provider will make an assessment of your diagnosis based on the following criteria:

  • Normal: Less than 5.7%
  • Prediabetes: Between 5.7 to 6.4%
  • Diabetes: 6.5% or higher

It is important to know that the A1C test is not appropriate for everyone. If you are pregnant, have been previously diagnosed with anemia (a condition characterized by the blood not having enough healthy red blood cells), or have recently undergone some other blood-related procedure like hemodialysis or blood transfusion, your healthcare provider might choose other tests to make a diagnosis. Additionally, the A1C test has not been well researched for diagnoses in non-White populations.

Oral Glucose Tolerance Test

For the oral glucose test, your blood sugar will be measured before and after drinking a sugary beverage given to you by your healthcare provider. The oral glucose test is meant to test how your body is processing sugar.

To complete the test, you will provide an initial blood sample to your healthcare provider. Then, you will drink a sugary drink containing approximately 75 grams of sugar. After taking the drink you’ll wait two hours and provide a second blood sample, at which point your sugar tolerance levels will be measured.

The blood sugar diagnostic measurements of the oral glucose tolerance test are:

  • Normal: Less than 140 milligrams per deciliter (mg/dl)
  • Prediabetes: 140 to 199 mg/dl
  • Diabetes: 200 mg/dl or higher

Fasting Plasma Glucose

The fasting plasma glucose test measures your blood sugar levels after fasting for a period of at least eight hours. This test is taken first thing in the morning and will require you to come into the healthcare provider's office or lab prior to eating breakfast. The criteria for the fasting plasma glucose test are:

  • Normal: Less than 100 mg/dl
  • Prediabetes: 100 mg/dl to 125 mg/dl
  • Diabetes: 126 mg/dl or higher

Random Plasma Glucose Test

A random glucose test, also known as a casual plasma glucose test, is a blood sugar test that can be taken at any time. Healthcare providers usually call for this test when a patient is demonstrating clear and severe symptoms of diabetes. During a random plasma glucose test, diabetes is diagnosed if your blood sugar is greater than or equal to 200 mg/dl.

Stages of Type 2 Diabetes Diagnosis

There are two stages of type 2 diabetes: prediabetes and type 2 diabetes itself. Gestational diabetes, or diabetes during pregnancy, is another type of type 2 diabetes.


Prediabetes is the initial stage of diabetes diagnosis. During prediabetes, your blood sugar levels are higher than average but have not yet reached the levels to be diagnosed with type 2 diabetes.

This stage is diagnosed with the standard diabetes diagnostic tests discussed above. Unfortunately, there are no clear symptoms of prediabetes.

There are a number of different risk factors that can lead to prediabetes, including:

African Americans, Hispanic/Latino Americans, American Indians, Pacific Islanders, and some Asian Americans have a greater incidence of prediabetes.

About 96 million people in the United States adults have prediabetes. A diagnosis of prediabetes is an indicator that over time, you could develop type 2 diabetes.

Type 2 Diabetes

Type 2 diabetes is the advanced stage of diabetes diagnosis, characterized by highly elevated levels of blood sugar. At this stage, you might start presenting more obvious symptoms of diabetes, including:

  • The urge to urinate more frequently
  • Feeling very thirsty or very hungry (even after you have eaten)
  • Extreme fatigue
  • Blurry vision
  • Wounds that are slow to heal
  • Tingling, pain, or numbness in the hands/feet

If you are experiencing any of these symptoms or any of the risk factors described above, your healthcare provider will use standard diabetes blood sugar tests to confirm your diagnosis and get you started on a treatment plan.

Gestational Diabetes

Gestational diabetes is a type of diabetes that can occur during pregnancy. Similarly to type 2 diabetes, this happens when your body doesn’t process insulin correctly, resulting in increased blood sugar. A diagnosis of gestational diabetes can put you at risk of developing type 2 diabetes after you've given birth.

Gestational diabetes is usually diagnosed 24–28 weeks into pregnancy during standard pregnancy checkups with your healthcare provider. This type of diabetes is diagnosed using a one- or two-step process that involves modified versions of the oral glucose tolerance test.

During the one-step process, you will have to fast overnight. The next day, you'll go to your healthcare provider's office where you will drink a sugary beverage containing 75 grams of sugar. Blood samples will be collected three times; at fasting, and after one and two hours of drinking the sugary beverage. Your healthcare provider will assess all three measurements and provide a diagnosis.

You will likely be diagnosed with gestational diabetes if your blood samples meet the following criteria:

  • Blood sugar levels higher or equal to 92 mg/dl at fasting
  • Blood sugar levels higher or equal to 180 mg/dl after one hour
  • Blood sugar levels higher or equal to 153 mg/dl after two hours

The two-step process involves the following:

  • Step one: You will drink a beverage containing 50 grams of sugar. Your healthcare provider will move you on to step two if your blood sugar levels are higher than 140 mg/dl after one hour.
  • Step two: After fasting overnight, you will drink a beverage containing 100 grams of sugar. Your healthcare provider will measure your blood sugar levels four times: after fasting, and at one, two, and three hours after drinking the beverage. It is likely that you will be diagnosed with gestational diabetes if your blood samples are considered high on two of the four samples tested.

Diabetes Comorbidities

Conditions that co-occur are referred to as comorbidities. Diabetes commonly occurs alongside a number of other health conditions. This is because diabetes shares risk factors with many other chronic health conditions, including cardiovascular diseases, hypertension (high blood pressure), lipid metabolism disorders, and osteoarthritis.

More recently, there has been an increase in the rate of mental health conditions diagnosed alongside diabetes. A 2019 study published in the scientific journal BMC Medicine reported high and increasing levels of depression in individuals with diabetes. The study, which evaluated comorbidity data over a period of 10 years, suggests that mental health conditions should be more closely monitored in people with diabetes moving forward because they can be a barrier for patients who should take the steps needed to manage their condition.

Common Differential Diagnoses

Healthcare providers use the tests described above to confirm a diabetes diagnosis. However, there are a variety of other conditions that present signs and symptoms similar to those of diabetes. Conditions and/or medications that can result in a differential diabetes diagnosis include:

  • Genetic irregularities in pancreatic cell function
  • Other metabolic syndromes
  • Infections
  • Endocrinopathies (diseases of the endocrine gland such as hyperthyroidism and hypothyroidism)
  • Complications of iron overload
  • Conditions affecting the pancreas such as pancreatitis, cystic fibrosis, etc.
  • Treatment with certain medications like corticosteroids, neuroleptics, and pentamidine

If you are undergoing testing for a diabetes diagnosis, it is important to tell your healthcare provider whether you have been previously diagnosed with any of these conditions or are actively taking some of the medications listed above.

A Quick Review

Type 2 diabetes is one of the most common public health issues, affecting many people around the world. Testing your blood sugar levels regularly will give your healthcare provider a clear picture of your health status and allow them to accurately provide you with a diagnosis. If you think you may be at risk of developing diabetes, talk to your healthcare provider about a potential diabetes screening.

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