How Type 2 Diabetes Is Diagnosed

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When diagnosing type 2 diabetes, doctors will perform a series of lab tests looking for markers of elevated glucose, or blood sugar. Lab tests are necessary, as type 2 diabetes may or may not have noticeable symptoms, or symptoms may crossover with other conditions. The diagnosis is often made during an annual physical or checkup. Your doctor may order a hemoglobin A1c test, a fasting blood sugar (FBS) test, or an oral glucose tolerance test (OGTT) as part of regular screening to check blood sugar levels and to help determine whether you have diabetes. Learn more about what these tests mean and how the condition is diagnosed.

Self-Checks/At-Home Testing

Recent estimates suggest there are more than 30.3 million people in the U.S. living with diabetes, and more than 1 in 4 adults with diabetes didn't know they had the disease.

While symptoms of diabetes may be hard to pinpoint, there are several signs that frequently coincide with high blood sugar and may be indicative of diabetes, such as:

  • Frequent urination
  • Frequent thirst
  • Excessive hunger
  • Extreme fatigue
  • Nerve tingling
  • Blurry vision
  • Cuts and bruises that are slow to heal

A buildup of blood sugar may also result in several skin conditions associated with diabetes, such as skin tags, small, harmless, polyp-type growths typically appearing on the eyelids, neck, and armpits; and acanthosis nigricans, marked by a dark, velvety patch of skin appearing in skin folds such as the back of the neck, armpits, elbow creases, hands, knees, and groin. Both conditions are thought to be related to insulin resistance.

If you think you might have diabetes, it's important that you get your assumptions confirmed by a doctor. Do not attempt to diagnose yourself by using over-the-counter testing equipment, such as a glucose monitor.

Labs and Tests

Typically, routine screenings for type 2 diabetes are recommended for most people every two years after age 45, especially for those who may be overweight. Routine screenings may be recommended by your physician if you're under 45 but have certain high-risk factors, like a family history of the disease, heart disease, high blood pressure, gestational diabetes, and/or a sedentary lifestyle.

Type 2 diabetes is usually primarily diagnosed with the hemoglobin A1c test, but if that test isn't available or you have a hemoglobin variant that makes testing difficult, your doctor will need to order another blood glucose test.

Your doctor may also perform additional tests to rule out type 1 diabetes, as elevated blood glucose levels can be present initially in both type 1 and type 2.

Hemoglobin A1c Test

The hemoglobin A1c test looks at the percentage of glucose that is attached to hemoglobin, a protein that makes up part of your red blood cells. The test gives a glimpse of your average blood sugar levels over the past two to three months, which is the approximate lifespan of red blood cells. One advantage of this test is that there is no required fasting and you don't have to drink a glucose-rich liquid, as in the oral glucose tolerance test.

A1c Result
Less than 5.7% Normal
5.7% to 6.4% Prediabetes
6.5% or higher Diabetes

Some people of African, Mediterranean, or Southeast Asian descent may have a genetic variation in their hemoglobin that could give falsely high or falsely low results. Your healthcare provider should take steps to ensure you have an accurate A1c result, or perform another test.

Random Plasma Glucose Test (RPG)

A random blood sugar test looks at your blood glucose levels regardless of when you've last eaten for a snapshot of your blood sugar status. This test is usually performed when healthcare professionals want to take a look at your blood sugar without having to wait for you to fast. This test is performed at any time. While a diagnosis of diabetes can be made with the help of this test, it is not usually used to diagnose prediabetes.

RPG Result
Less than 200 mg/dl Normal
200 mg/dl or higher Diabetes

Fasting Plasma Glucose (FPG)

The FPG test looks at your fasted blood glucose levels at a single point in time. A fasting test means that you can't eat for eight to 10 hours before you have your blood drawn. Most doctors recommend getting tested first thing in the morning after fasting all night.

FPG Result
99 mg/dl or below Normal
100 mg/dl to 125 mg/dl Prediabetes
126 mg/dl or higher Diabetes

Fasting glucose higher than 126 mg/dl indicates that you have type 2 diabetes. Your doctor will likely repeat the fasting blood sugar test on two separate occasions to confirm the diagnosis.

Oral Glucose Tolerance Test (OGTT)

The OGTT is a glucose challenge test. Fasting blood glucose is usually taken first to establish a baseline level. Then you are given a drink that contains 75 grams of glucose (sugar). Two hours later another blood sample is drawn to check your glucose level.

OGTT Result
139 mg/dl or below Normal
140 mg/dl to 199 mg/dl Prediabetes
200 mg/dl or higher Diabetes

If your glucose is over 200 mg/dl, then a diagnosis of type 2 diabetes is likely. Again, your doctor will usually perform this test on two different occasions before a confirmed diagnosis is made.

If You Are Pregnant

The OGTT is a little different if your doctor orders it when you are pregnant as a routine test for gestational diabetes. The glucose drink is typically 50 grams of glucose instead of 75, and the blood glucose level is drawn after one hour instead of two. If your blood glucose level comes back less than 140 mg/dl, then you have normal glucose tolerance. If it comes back over 140 mg/dl, then it is considered abnormal and you will need further testing.

Differential Diagnoses 

Beyond type 2 diabetes, there are several other conditions that may be at play and could result in similar symptoms or even possibly bloodwork showing elevated glucose levels.

Prediabetes

Insulin resistance or impaired glucose tolerance may be affecting how your body processes and metabolizes glucose, but you may not be in the midst of full-blown type 2 diabetes just yet. If you have prediabetes, your doctor can help you craft a treatment plan to make lifestyle changes in order to prevent the disease from progressing.

Type 1 Diabetes or Latent Autoimmune Diabetes in Adults

Symptoms of type 1 diabetes may appear very similar to type 2 diabetes, though they tend to come on all at once in a short timespan. Bloodwork may also still show glucose elevation when standard tests are performed, but your doctor should be able to add on additional testing to confirm whether you have type 1 (which may be latent autoimmune diabetes in adults or LADA) by looking at certain antibodies and proteins in your blood.

Metabolic Syndrome

Elevated blood sugar is just one piece of the constellation of factors contributing to metabolic syndrome, which is thought to be linked to insulin resistance. Other criteria for the diagnosis of metabolic syndrome include three of five of the following factors:

  • Waist circumference over 35" for women or 40" for men
  • Triglyceride level above 150 mg/dl
  • High-density lipoprotein (HDL) cholesterol below 40 mg/dl
  • Blood pressure above 130/85 mm/Hg
  • Fasting blood glucose level above 100 mg/dl

Treatment for metabolic syndrome includes modification of many lifestyle factors including diet, exercise, and stress, but risk factors usually decrease with positive changes.

Hyperthyroidism

Mild hyperglycemia (high glucose levels) and symptoms such as fatigue, tingling, anxiety, and weight loss may be associated with hyperthyroidism or overactivity of the thyroid gland and overproduction of thyroxine. Your doctor may perform additional testing to check for sufficient thyroid function before ruling out this diagnosis.

A Word From Verywell 

If you receive a diagnosis of diabetes, work with your healthcare team to create a multifaceted treatment plan, incorporating diet, exercise, medication, supplements, and stress relief. In fact, according to the American Diabetes Association, research shows that you can reduce your risk of type 2 diabetes and possibly even reverse the condition by losing just 7% of your body weight (for example, losing 15 pounds if you weigh 200 pounds) and working in moderate exercise such as brisk walking, swimming, or cycling for 30 minutes, five days per week.

Type 2 Diabetes Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

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