Diagnosing Type 2 Diabetes in Adults

NYU Langone doctors are experts at identifying people with type 2 diabetes, a condition in which a person has chronically high levels of blood sugar. It occurs when the body lacks or is resistant to insulin, a hormone that helps the body use glucose, or sugar. As a result, the body is unable to convert glucose into energy.

In prediabetes, a person has higher-than-normal levels of blood sugar, which increases the risk of developing type 2 diabetes. To help the body use some of the excess blood sugar levels, the pancreas produces more insulin. Over time, prediabetes may progress into type 2 diabetes. 

In most people, insulin resistance and type 2 diabetes develop gradually. If you have prediabetes and take steps to prevent type 2 diabetes, you may be able to avoid it altogether.

Risk Factors

Being overweight, especially if you are age 45 or older, is the biggest risk factor for type 2 diabetes. In particular, people who are “apple-shaped”—meaning they carry more fat around the abdomen—have a higher risk. Experts believe excess belly fat produces hormones that increase inflammation, which can lead to insulin resistance.  

Being sedentary also raises the risk of type 2 diabetes. It can lead to weight gain and lower muscle mass, which is required to help use glucose efficiently.

People with a family history of type 2 diabetes have a greater chance of developing the condition than those who don’t. The condition can also occur in women with polycystic ovarian syndrome, a hormone disorder associated with weight gain and insulin resistance.

Conditions that harm insulin-producing cells in the pancreas, such as pancreatic cancer and pancreatitis, also increase the risk of developing type 2 diabetes. 

Metabolic Syndrome

Metabolic syndrome is a cluster of conditions that puts you at risk of developing type 2 diabetes. People with metabolic syndrome are more likely to develop type 2 diabetes than those who don’t have it.  

Metabolic syndrome occurs when you have at least three of the following conditions: hypertension, or high blood pressure; hyperlipidemia, commonly known as high cholesterol; high blood sugar levels; and obesity, especially excess abdominal fat.

Signs and Symptoms

Initial signs and symptoms of type 2 diabetes may be subtle and are often overlooked. The most common symptom is frequent urination, which occurs because the kidneys eliminate excess sugar through urine. The loss of fluid can cause dehydration, making you thirstier than usual.

High blood sugar levels can cause changes in the lens of the eye, making your vision blurry. 

Many people with type 2 diabetes feel tired, because insulin resistance prevents the body from getting the energy it needs.

Long-Term Effects

Having chronically high blood sugar levels can damage blood vessels and nerves throughout the body, causing a variety of serious health problems. 

Many people with type 2 diabetes develop nerve damage, known as diabetic neuropathy, especially in the feet. People with this condition may experience pain, tingling, and numbness in the affected area.

Diabetic neuropathy increases the risk of a variety of foot problems. These include foot ulcers, which can become infected, and a weakening of bones and joints known as Charcot foot

People with type 2 diabetes are also at risk for peripheral artery disease, including a blockage in the arteries that supply blood to the legs and feet known as lower extremity arterial disease. Infections and poor circulation in the legs and feet may eventually cause severe tissue damage, which may require amputation. 

Damage to nerves in a man’s reproductive system can cause erectile dysfunction.

Type 2 diabetes can harm blood vessels in the retina, the light-sensitive layer of cells in the back of the eye, causing a condition known as diabetic retinopathy. This condition can eventually lead to vision loss or blindness. In fact, diabetic retinopathy is a leading cause of preventable blindness in the United States. 

The condition can also damage cells and blood vessels in the kidneys, preventing them from effectively eliminating wastes from the body. Diabetic kidney disease is the most common cause of kidney failure.

People with prediabetes and type 2 diabetes also have a higher risk of developing blockages in arteries in the heart and brain, increasing the risk of heart attacks or stroke. Heart disease and stroke are more common in people with diabetes than in people who do not have the condition.

Diagnostic Tests

NYU Langone doctors diagnose type 2 diabetes based on the results of blood tests that measure blood sugar levels.

Often, these tests are performed during an annual physical exam. Some blood tests may be performed more frequently if you have prediabetes or risk factors for type 2 diabetes. Other tests are used to monitor for signs of metabolic syndrome.

Fasting Blood Sugar Test

A fasting blood sugar test provides a snapshot of your blood sugar level before you have eaten. The doctor measures the amount of sugar in your blood after you’ve fasted for at least eight hours—usually overnight. 

A fasting blood sugar level of 100 to 125 milligrams per deciliter indicates that you have prediabetes. A blood sugar level of 126 milligrams per deciliter or higher on two separate tests means you have diabetes.

Hemoglobin A1C Test

The hemoglobin A1C is a highly sensitive and accurate blood test for diagnosing type 2 diabetes. It measures your average blood sugar level over a two- or three-month period to determine whether it is consistently high. 

Because the sugar remains attached to hemoglobin—a protein in red blood cells that carries oxygen to tissues throughout the body—for up to four months, it’s a good indicator of average blood sugar levels. If two separate tests find that 5.7 percent of your hemoglobin is glycated, or coated with sugar, you have prediabetes. If 6.5 percent or more of your hemoglobin is glycated, you have type 2 diabetes. 

Oral Glucose Tolerance Test

In an oral glucose tolerance test, you fast overnight, then a doctor or nurse draws blood and measures your blood sugar level. Next, you drink a liquid that contains 75 grams of glucose and tastes like a noncarbonated soda. Additional blood samples are taken one and two hours after drinking the liquid to see how much your blood sugar level has changed. 

A level of 200 milligrams per deciliter or higher after 2 hours indicates you have diabetes. A level of 140 to 199 milligrams per deciliter suggests prediabetes.

Lipoprotein Panel

A lipoprotein panel is a blood test that measures your total cholesterol level, including the “bad” form (known as low-density lipoprotein, or LDL) and the “good” form (known as high-density lipoprotein, or HDL).

Bad cholesterol is associated with atherosclerosis, a narrowing of the arteries. Good cholesterol helps remove artery-clogging plaque, a substance composed of calcium, cholesterol and fat.

The blood test also measures triglycerides, a type of fat that increases the risk of heart disease. 

Kidney Function Tests

Doctors may order additional laboratory tests to evaluate your kidney function, which can be impaired if you have diabetes.

For instance, a urine microalbumin test measures the amount of albumin, a protein found in the blood, in your urine. As kidney function worsens, the kidneys leak more protein into the urine. The urine microalbumin level test is the most sensitive type of test to measure protein in urine.

Our doctors also perform a blood test to measure how much creatinine—a waste product that forms when muscle tissue breaks down—is in your blood. Creatinine levels increase as kidney function becomes impaired.

Measuring creatinine levels also helps to estimate the glomerular filtration rate, which reveals how well the kidneys can remove waste and excess fluid from blood. Creatinine levels increase as the glomerular filtration rate decreases, meaning that kidney function has become impaired.

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