How Type 2 Diabetes Is Diagnosed

Diagnosing type 2 diabetes requires a series of lab tests looking for markers of elevated glucose, or blood sugar. Such tests are necessary, as type 2 diabetes may or may not have noticeable symptoms, or symptoms may crossover with other conditions.

The diagnosis often is made during an annual physical or checkup. Your healthcare provider 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 if you have diabetes.

Self-Checks/At-Home Testing

According to the latest data available from the Centers for Disease Control and Prevention (CDC), more than 37.3 million Americans, or about 11% of the population, has diabetes.

An additional 96 million American adults, or approximately 38% of the population, has prediabetes. Despite increased awareness efforts, many people with diabetes or prediabetes continue to be unaware of their condition.

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 skin conditions associated with diabetes—in particular:

• Skin tags: Small, harmless, polyp-type growths typically appearing on the eyelids, neck, and armpits
• Acanthosis nigricans: Dark, velvety patch of skin 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 to consult with your healthcare provider and get a confirmed diagnosis. Do not attempt to diagnose yourself by using over-the-counter testing equipment, such as a glucose monitor.

Labs and Tests

Routine screening for type 2 diabetes is recommended for everyone every three years beginning at age 35, and more frequently if symptoms develop or risks change (i.e., weight gain). Your healthcare provider may also recommend screening for adults with obesity or overweight who have one or more of the following known risk factors for diabetes:

• Family history of diabetes
• HDL cholesterol level less than 35 mg/dL OR triglyceride level greater than 250 mg/dL
• History of gestational diabetes
• History of heart disease
• Hypertension (140/90 mmHg or higher)
• Physical inactivity
• Polycystic ovary syndrome (PCOS)
• Conditions associated with insulin resistance
  

Type 2 diabetes usually is diagnosed with the hemoglobin A1C test, but if that test isn't available or you have a hemoglobin variant that makes testing difficult, your healthcare provider will need to order another blood glucose test.

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 it does not require fasting.

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.

Random Plasma Glucose Test (RPG)

A random blood sugar test looks at 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 and so it can be 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.

Fasting Plasma Glucose (FPG)

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

Fasting glucose higher than 126 mg/dL indicates type 2 diabetes. Your healthcare provider 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.

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

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 blood work 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 healthcare provider 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 time span. Blood work may also still show glucose elevation when standard tests are performed, but your healthcare provider 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 out of five of the following factors:

• Waist circumference over 35 inches for women or 40 inches 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 healthcare provider may perform additional testing to check for sufficient thyroid function before ruling out this diagnosis.

Type 2 Diabetes Healthcare Provider Discussion Guide

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

Download PDF

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Summary

If you're diagnosed with diabetes, there's a lot you can do to prevent it from worsening, starting with losing weight. According to the American Diabetes Association, overweight and obese people with diabetes can benefit greatly from losing just 5% of their total body weight; a loss of 15% or more is the most effective. People with prediabetes can prevent it from progressing to diabetes by shedding just 7% to 10% of body weight.

This doesn't mean you'll need to dramatically cut back on your eating: Your healthcare team can help you create a weight loss plan that includes not only a healthy and satisfying diet, but also moderate exercise (brisk walking, swimming, or cycling for 30 minutes, five days per week) along with medication if necessary, supplements, and stress-management practices. In some ways, while obviously unwelcome, a diabetes diagnosis can mean positive changes in your health and well-being you may not have made otherwise.