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How is Diabetes Diagnosed?

Updated: Jan 21, 2022

vial of blood being tested for diabetes and A1C

Many people are curious as to how diabetes is diagnosed, as they want to make sure they *really* have it. Bloodwork is always involved, as diabetes cannot be diagnosed by symptoms alone. However, there isn’t just one blood test that can provide a diabetes diagnosis.

Part 1 – Getting the Numbers

One blood test that can be done to check for diabetes is a fasting plasma glucose, also known as a fasting blood sugar. This is done after fasting for at least 8 hours. You’re generally encouraged to drink water before having blood drawn, but don’t have anything with sugar! I’ve seen many people receive invalid results because they drank some coffee with sugar in it before they had their blood drawn. A fasting reading of 126mg/dL or higher would be in the diabetes category.

Another blood test that can be done is a hemoglobin A1C, often called an A1C for short. This test is nice because you don’t have to fast for it to be done. A reading is 6.5% or higher is consistent with a diabetes diagnosis.

The third option for a blood test is an oral glucose tolerance test. You will drink a sugary drink that contains 75g of glucose and then have your blood taken 2 hours after. A blood sugar reading of 200mg/dL or higher would be in the diabetes category.

Part 1 – Confirming the Diagnosis

According to the American Diabetes Association (ADA), to get an official diabetes diagnosis, there must be two results that fall into the diabetes category. These results could be for the same blood test, or two different ones. For example, if you had bloodwork done and your fasting blood sugar was 135 and your A1C was 6.9%, this would be enough information to give a diabetes diagnosis since there were two values above the diagnostic threshold. However, if you only had one value come back in the diabetes category (say maybe your doctor only ordered a fasting blood sugar, not an A1C) another set of blood work should be done as soon as possible to confirm. This bloodwork can be the same test that was done the first time, or one of the other options.

There is an exception to the rule that the diagnosis must be confirmed. If you have a blood sugar reading of 200 or more (doesn’t need to be fasting) and have symptoms of diabetes (frequent thirst, frequent urination, etc.) then a confirmation is not required.

Final Thoughts

If you recently had blood work done, don’t always assume no news is good news. If you do have diabetes based on your lab results, most offices have a nurse call you to let you know about the diagnosis. However, some offices or providers may choose to wait and tell you at your upcoming visit. This way, it can be discussed face-to-face directly with your provider and you will be able to ask them questions directly. Make sure to keep your appointments!

If you are told to have repeat blood work done, don’t drag your feet. Being told you have diabetes can be scary, but a timely diagnosis can set you up for success.

Feeling overwhelmed with a recent diagnosis? Schedule an appointment with a dietitian and/or diabetes educator to get answers to your questions and come up with a plan!



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