How Diabetes Blood Testing Works

Lab Testing FAQs > All About Diabetes Testing

Diabetes is a group of diseases that impair the body’s ability to process glucose, resulting in blood sugar levels that are too high. According to the CDC, 34.2 million adults in the United States have diabetes—and as many as 1 in 5 of those adults don’t know they have it. 

The number of adults with prediabetes is even more staggering: more than 88 million U.S. adults—over a third of this demographic—have prediabetes, and approximately 84% of those adults are unaware that they have it.

Diabetes is the seventh leading cause of death in the United States, and the number one cause of kidney failure, lower limb amputations, and adult blindness. There is currently no cure for diabetes, which is why testing and lifestyle adjustments are the recommended protocol for diabetes treatment and prevention. 

In the age of COVID-19, diagnostic testing for diabetes is even more essential; having diabetes increases a patient’s risk of developing severe illness from COVID-19, and if they are unaware that they have diabetes, they will not be aware of this increased risk. 

Below, learn about the different types of diabetes and recommended diabetes tests.

What are the Different Types of Diabetes?

There are three main types of diabetes: type 1, type 2, and gestational diabetes. All three conditions occur when the body does not produce enough insulin or does not use insulin correctly. Insulin is an important hormone that regulates the amount of glucose in the blood; when the body doesn’t produce enough, blood sugar levels become too high. Prediabetes is a related condition in which blood sugar levels are higher than normal, but not yet high enough to be diagnosed as diabetes. 

Type 1 Diabetes

Type 1 diabetes is a chronic condition that is believed to be caused by an autoimmune reaction. When a patient has type 1 diabetes, their immune system mistakes pancreatic cells as foreign invaders and attacks them, preventing them from making insulin. Patients with type 1 diabetes need to take insulin every day to manage their blood sugar levels.

Some patients have certain genes that make them more likely to develop type 1 diabetes, and environmental triggers may also play a role. Type 1 diabetes is usually diagnosed in infants, children, teens, and young adults. Approximately 5-10% of people who have diabetes have type 1.

Type 2 Diabetes

Type 2 is the most common type of diabetes, accounting for 90-95% of all cases. When a patient has type 2 diabetes, their cells don’t respond normally to insulin—a condition known as insulin resistance. As a result, the pancreas cannot keep blood sugar at normal levels.

It usually takes several years to develop type 2 diabetes and may not have noticeable symptoms, especially in the early stages of the disease. Type 2 diabetes can be prevented or delayed with healthy lifestyle changes such as losing weight and eating healthier foods.

Gestational Diabetes

Gestational diabetes develops during pregnancy in women who did not already have diabetes before becoming pregnant. The cause of gestational diabetes is unknown, but many women do experience some amount of insulin resistance during the later stages of pregnancy.

Every year, up to 10 percent of pregnancies in the U.S. are affected by gestational diabetes. When a patient is diagnosed with gestational diabetes, it does not mean they will necessarily have diabetes after giving birth; however, proper management during the pregnancy is key. 


Prediabetes is a health condition in which blood sugar levels are higher than normal, but not high enough yet to be diagnosed as type 2 diabetes. Roughly 1 in 3 adults in the United States have prediabetes, and as many as 84% of them do not know they have it. 

Patients with prediabetes have a higher risk of developing type 2 diabetes, as well as other conditions such as heart disease. However, it is possible for a patient with prediabetes to significantly lower their risk of developing type 2 diabetes through lifestyle changes. 

What Are the Most Common Diabetes Tests?

Testing for diabetes is quick, easy, and straightforward. A simple blood test is all it takes to find out if you have prediabetes or type 1, type 2, or gestational diabetes. 

A1C Test

The A1C test is one of the most common tests for diabetes because the results provide an average measurement of blood sugar levels over the past two to three months. This test can be used to diagnose prediabetes and diabetes, as well as monitor treatments over time. Fasting is not required for the A1C test. A1C test results are reported as a percentage:

  • Results of less than 5.7% are considered normal.
  • Results between 5.7% and 6.4% indicate prediabetes.
  • Results equal to or greater than 6.5% indicate diabetes.

Fasting Blood Sugar Test

A fasting blood sugar test measures the patient’s blood sugar after fasting overnight, which generally means not eating for between eight and twelve hours before the test. 

  • Results of less than 100 mg/dL are normal.
  • Results between 100 and 125 mg/dL indicate prediabetes.
  • Results equal to or greater than 126 mg/dL after two tests indicate diabetes.

Random Blood Sugar Test

A random blood sugar test measures the patient’s blood sugar at any point in time, regardless of when they last ate. Fasting is not required for a random blood sugar test. Results equal to or greater than 200 mg/dL indicate diabetes.

Glucose Tolerance Test

A glucose tolerance test consists of two separate tests: one before consuming a liquid that contains glucose, and a second test two hours later. The goal of a glucose tolerance test is to determine how efficiently the body responds to glucose. This test is usually recommended for diagnosing gestational diabetes. Fasting is required before the first test.

  • Results of less than 140 mg/dL are considered normal.
  • Results between 140 and 199 mg/dL indicate prediabetes.
  • Results equal to or greater than 200 mg/dL indicate diabetes.

Who Should Be Tested for Diabetes?

Diabetes may not cause symptoms, especially in the early stages of the disease. For this reason, it is incredibly important to get tested for diabetes when patients experience any of the following symptoms:

  • Urinating frequently, especially at night
  • Feeling very thirsty
  • Feeling very hungry
  • Extreme fatigue
  • Blurry vision
  • Sores, cuts, and bruises heal slowly
  • Having more infections than normal
  • Losing weight without trying (type 1)
  • Numb or tingling hands or feet (type 2)

Additionally, patients with high-risk factors should be tested for diabetes even if they are not experiencing symptoms. This includes patients who:

  • Are overweight (body mass index greater than 25)
  • Are over the age of 45
  • Have a family history of diabetes
  • Are Black, Hispanic/Latino, American Indian, Asian American, or Pacific Islander
  • Have high blood pressure, low HDL cholesterol, or high triglycerides
  • Are physically inactive
  • Have been diagnosed with polycystic ovary syndrome (PCOS)
  • Have been diagnosed with gestational diabetes

It is also important for all pregnant patients to be tested for gestational diabetes between the 24th and 28th weeks of pregnancy. 

Over the past two decades, the number of adults diagnosed with diabetes in the United States has more than doubled. Diabetes is a serious condition that can cause complications if not properly diagnosed or managed. Fortunately, it is possible to delay or prevent the development of prediabetes and type 2 diabetes through lifestyle changes. Additionally, medical therapies and treatments can successfully manage all types of diabetes. 

Early detection is the key to preventing complications associated with diabetes. If you are experiencing any symptoms or have a higher risk of developing diabetes, schedule a blood test with your doctor as soon as possible.

Before you go…