How Do You Diagnose Type 2 Diabetes

According to CDC, 90-95% of the diabetes cases are Type 2 Diabetes. Even though Type 2 Diabetes can happen at any time of your life, it usually happens after the age of 45 years old. Type 2 Diabetes is also called adult-onset diabetes.

Testing for Type 2 Diabetes

Type 2 Diabetes is usually diagnosed through blood tests that measure the amount of blood sugar (glucose) in the body:

  • Glycated hemoglobin (A1C) test: this blood test reviews your average blood sugar level for the past two to three months.
  • Fasting Plasma Glucose (FPG) test: this blood test is taken after you fasted overnight. It shows your blood sugar (glucose) level at the time you get the blood draw.
  • Oral Glucose Tolerance Test (OGTT): you will likely to see this test during pregnancy, but is used less elsewhere. It takes 2 hours in total to complete. First, you have to fast over 8 hours before the test. And you will be given a sugary liquid to drink. Your blood will get draw at: before the drink, 1-hour after the drink, 2-hour after the drink, and sometimes 3-hour after the drink.
  • Random Plasma Glucose (RPG) test: this test reflects the blood sugar (glucose) level at the point you get your blood drawn. To get this test, you do not need to fast.

How to Interpret the Result

The following table shows the normal ranges if you are not pregnant.

Diagnosis A1C (percent) Fasting Plasma Glucose (FPG)* Oral Glucose Tolerance Test (OGTT)** Random Plasma Glucose Test (RPG)*
Normal Below 5.7 99 or below 139 or below
Prediabetes 5.7-6.4 100-125 140 to 199
Diabetes 6.5 or above 126 or above 200 or above 200 or above
*Glucose values are in milligrams per deciliter, or mg/dL.
**At 2 hours after drinking 75 grams of glucose. To diagnose gestational diabetes, health care professionals give more glucose to drink and use different numbers as cutoffs.
Source: Adapted from American Diabetes Association. Classification and diagnosis of diabetes. Diabetes Care. 2016;39(1):S14-S20, tables 2.1, 2.3.

All tests use different measuring techniques. So doctors usually need to repeat the same test or have two or more tests done to confirm a diagnosis. This means, if your number is high for two separate tests, you are likely diagnosed with diabetes.

Who Should Get Tested?

Some people may get their sugar tested because they have noticeable symptoms. Most people get diagnosed with routine tests. Routine screening usually starts at the age of 45. However, if you have risk factors below, you may want to follow the test more closely:

  • Overweight or obese
  • Sedentary lifestyle
  • Family history of diabetes
  • History of gestational diabetes or had a baby over 9 pounds at birth
  • African-American, Native American, Latino, Asian, or Pacific Islander descent
  • High triglyceride and/or low HDL (good cholesterol)

If the test results are normal, repeat the test every 3 years. If you are at borderline, ask your doctor when to come back for another test.

Even though a diagnosis of Type 2 Diabetes may sound scary, there are still things you can do to reduce medications and complications down the road. Many people with diabetes live a life free of complications with their diabetes well-controlled by eating a healthy diet and being active. With a better understanding of how diabetes is diagnosed, you may want to take action to prevent diabetes if you are at high risk, or you may set goals with controlling your blood sugar if you are diabetic.