Tests to Diagnose Diabetes


Diabetes is one of the most common and long-term diseases globally. Proper diagnosis may help prevent and may even lead to proper diabetes treatment. Diabetes can be diagnosed and confirmed through blood tests. Health care providers commonly use the A1C test or the fasting plasma glucose (FPG) test in diagnosing diabetes.

Fasting Plasma Glucose (FPG) Test

This test is used to diagnose diabetes. This test involves fasting and is usually done in the morning while you have not eaten anything and have drunk only water. Since you will be fasting for 8 hours before the test in the morning, the results are more reliable.

A1C Test

This test offers you insights on your average blood sugar levels over the past three months. There is no fasting required for this test. Age, anemia or other problems related to the blood will be taken into consideration for this test.

The results will be mentioned as a percentage of A1C. If your percentage is high, it indicates that the average amount of blood sugar levels is also high.

Random Plasma Glucose (RPG) Test

This test can be done anytime without fasting. When you have symptoms of diabetes, your health care team might use this test, if they don’t want to wait for your fasting blood sugar levels.

Diagnosing Gestational Diabetes

Gestational diabetes develops only during pregnancy. Expectant moms may take the glucose challenge test, the oral glucose tolerance test, or both to find out whether they have gestational diabetes.

Glucose Challenge Test

This test is also called glucose screening test. Your health care provider will test your blood after you have consumed glucose-containing sweet liquid. There is no fasting required for this test.

Oral Glucose Tolerance Test (OGTT)

The OGTT determines your blood sugar levels and requires a minimum of 8 hours fasting. Your blood sample will be collected, after which you have to drink glucose drink. For the next two to three hours, your blood will be drawn for testing. If your blood sugar levels are high in any of the two test results, you may have gestational diabetes.

This test can also be used to diagnose diabetes and prediabetes. Because of the complexity and cost of this method, FPG test is mostly preferred.

What Does Your Test Numbers Mean?

For detecting prediabetes and diabetes, every test has various measurement ranges. To confirm diabetes, you have to take the same test repeatedly. In some cases, you may have to take another test for confirmation.

Diagnosis A1C (percent) Fasting plasma glucose (FPG) Oral glucose tolerance test (OGTT) Random plasma glucose test (RPG)
Normal 5.7 99 or below 139 or below
Prediabetes 5.7 to 6.4 100 to 125 140 to 199
Diabetes 6.5 or above 126 or above 200 or above 200 or above

Note:  Normal range differs for pregnant women and it is not included in this table.

Diabetes can be confirmed using these above-mentioned tests; however they cannot identify or diagnose the type of diabetes. Sometimes, it will be hard to distinguish between type 1 and type 2 diabetes. Monogenic diabetes, which occurs in babies, can be mistaken for type 1 diabetes. The presence of diabetes-specific autoantibodies shows that a person has type 1 diabetes. The treatment of diabetes depends on its type; hence, determining which type of diabetes you have is very important.

Over-the-counter glucose meters cannot diagnose diabetes, so consult your health care professional if you have symptoms of diabetes. Preventing or managing diabetes can save you from dangerous and life-threatening complications!


-Medical Observer

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