Types of Blood Tests to Diagnose Diabetes and Prediabetes

Types of Blood Tests to Diagnose Diabetes and Prediabetes

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  • The normal fasting blood glucose level is less than 100 milligrams per deciliter (mg/dL). If your level is between 100 to 125 mg/dL, you may have prediabetes. A level that’s 126 ml/dL or higher, if seen consistently on at least two FPG tests, means that you have diabetes
  • The random plasma glucose test is usually conducted only on people who have severe diabetes, particularly those who are experiencing the hallmark symptoms (frequent urination, unexplained weight loss, excessive thirst, etc.). If results show glucose levels greater than or equal to 200 mg/dL, then it means you have diabetes

People who are exhibiting symptoms of diabetes, as well as those who have a high risk of acquiring this illness, should consider getting a diabetes test to confirm. There are several types of diabetes tests available today, and most of them rely on blood testing to check for glucose levels.

If you think that you're exhibiting symptoms of diabetes, it's crucial to consult a physician to confirm your diagnosis. Do not attempt to self-diagnose — keep in mind that testing equipment like blood glucose meters, which you can buy over the counter from pharmacies, cannot diagnose diabetes.1 A physician would recommend any of the blood tests below to check if you have diabetes:2,3

Fasting Plasma Glucose Test (FPG)

The American Diabetes Association recommends the FPG as it's easy, convenient and is less costly than other tests. This is also preferred for diagnosing diabetes in men, non-pregnant women and children. It works by measuring your blood glucose levels after doing an overnight fast (no meals for at least eight hours).

The normal fasting blood glucose level is less than 100 milligrams per deciliter (mg/dL). If your level is between 100 to 125 mg/dL, it means you may have prediabetes. A level that's 126 ml/dL or higher, if seen consistently on at least two FPG tests, means that you have diabetes.

Oral Glucose Tolerance Test (OGTT)

Often performed after an FPG test, this is usually done if you have normal fasting blood glucose levels, but diabetes is still suspected, either because you're showing symptoms or have risk factors for this disease.

This is because some people have normal fasting blood sugar reading although their blood sugar rises rapidly during meals. This means they have an impaired glucose tolerance, and if their levels are high enough, they could be diagnosed with diabetes. The OGTT is also recommended during pregnancy, to diagnose gestational diabetes.

Your doctor will ask you to fast overnight and then drink a sweet liquid with 75 grams of glucose. Two hours later, a sample of your blood will be taken and sent for analysis. The normal levels are less than 140 mg/dL after two hours. If you have a level of 200 mg/dL or higher after two hours, then it means you have diabetes. Prediabetes means having levels at 140 to 199 mg/dL after two hours.

Hemoglobin A1C Test

This blood test checks how much sugar is stuck to your hemoglobin, or red blood cells, which have a three-month lifespan. Originally, it was used to check the glucose levels of people that are diagnosed with diabetes, but today, it's also used for diagnosing prediabetes and Type 2 diabetes.

Unlike the two previously mentioned tests, the A1C test does not require you to fast. However, there are some people who are not advised to have this test, such as people with anemia or blood disorders, pregnant women and patients who have recently suffered blood loss or has had a transfusion.

An A1C level of 6.5 to 7 percent may indicate that you have diabetes. Normal results should be around 4 to 6 percent.4

Random Plasma Glucose Test

Also called Casual Plasma Glucose Test, this is actually a blood check that can be done any time of the day. However, it is not considered a preferred diagnostic test by the ADA.

The random plasma glucose test is usually conducted only on people who have severe diabetes, particularly those who are experiencing the hallmark symptoms (frequent urination, unexplained weight loss, excessive thirst, etc.). If results show glucose levels greater than or equal to 200 mg/dL, then it means you have diabetes.

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