What is Involved in a Diabetes Test?

Diagnosing diabetes and pre-diabetes can be done with a simple blood test. People who exhibit the symptoms or have risk factors associated with diabetes often undergo diabetes testing. The same types of blood tests used to diagnose diabetes are also often done to monitor the condition as well. A diabetes test is performed on a doctor’s order and is usually done in a clinical laboratory or the doctor’s office.

A diabetes test involves the collection of blood to be sent for glucose testing. The glucose levels in the blood indicate whether levels are within or out of normal range. There are three basic types of diabetes tests – fasting plasma glucose test (FPG), oral glucose tolerance test (OGTT), and random plasma glucose test, which is also called a casual glucose test. The primary difference between a casual glucose test and the FPG or OGTT is fasting. A random plasma glucose test is a glucose measure taken without regard to food consumption while the FPG and OGTT are both performed after a minimum of 8 hours fasting.


The fasting plasma glucose test is one of the most common diabetes test performed because it is inexpensive. The test yields the most accurate results when performed in the morning. It is also simpler to achieve the minimum fasting time of eight hours if the test is performed early in the day. The test is performed by simply drawing blood, which is then tested for glucose levels. Normal range is 99 milligrams per deciliter (mg/dL) while 100-125 mg/dL indicates a form of pre-diabetes and 126 mg/dL or higher is diabetic. Confirmation is typically required by repeating the test on a different day to ensure similar ranges upon repeat.

In some cases, the FPG can miss certain types of diabetes and pre-diabetic conditions. This is where an oral glucose tolerance test is useful. An OGTT is performed much the same way as the FPG, but involves drinking a special liquid glucose substance. Blood is collected immediately before administration of the substance and two hours afterwards. The result ranges for this test are different than the FPG and a level of 200 mg/dL indicate diabetes if confirmed in a repeat test.

Random glucose testing levels of 200 mg/dL or higher can also indicate diabetes if combined with other symptoms, such as increased urination, excessive thirst, unexplained weight loss, and fatigue. Typically, one of the more accurate fasting tests will be administered to confirm diabetes. The type of diabetes test that diabetics use to monitor glucose levels at home is also considered a type of random glucose testing.

Another type of diabetes test, which is also performed by a simple blood test, is the A1C test. This blood test measures hemoglobin to give blood glucose averages over an extended period of time. The test is often performed to diagnose both Types 1 and 2 diabetes as well as to see how well a patient is managing his or her diabetes. This test also does not require fasting.

Your doctor may order a diabetes test if you exhibit signs of diabetes or if you have risk factors associated with diabetes, including family history, obesity, or previous gestational diabetes. Regardless of the type of test used to confirm diagnosis, a simple blood test is all that is required and confirmation is essential to managing this disease and preventing the health problems associated with it.



Discuss this Article

Post 1

I think I have diabetes. I'm really fat, and I get bad headaches all the time and am tired, thirsty and need to pee constantly. Type 2 for sure. Gah.

Post your comments

Post Anonymously


forgot password?