How to Test for Diabetes and the Best Tests for Diagnosis

A healthcare professional will likely recommend a diabetes test if you're age 35 or older and have one or more risk factors for diabetes, or symptoms of diabetes. A hemoglobin A1C (HbA1C or A1C) is a blood test often used for this, but it’s not the only test. And if you have diabetes or an abnormal result, you’ll likely need more than one test to sort out the next steps. 

Aside from an A1C test, you may need to get a blood glucose (sugar) level, a urine test, or an oral glucose tolerance test (OGTT). 

What are the symptoms of diabetes?

Anyone can develop diabetes, so it’s important to know the most common symptoms. Symptoms of diabetes are caused by higher than normal blood sugar (glucose) levels. They can come on slowly over time or start very suddenly. Symptoms can also vary from person to person, but they typically include:

• Increased hunger and thirst

• Frequent urination

• Dry mouth

• Fatigue

• Blurry vision

• Weight loss

That said, not everyone with diabetes has symptoms. But diabetes can cause long-term complications if it’s undiagnosed and untreated. That’s why testing is recommended if you’re age 35 or older, or if you have a high risk for diabetes.

How to test for diabetes

Let’s take a deeper look at the five diabetes tests healthcare professionals most commonly order. We’ll dig into what the results might show and how often you should have testing in the future. 

1. Hemoglobin A1C blood test

The A1C test is the most common diabetes test. It’s quick, convenient, and reliable. An A1C gives information about your glucose over time, rather than your level at any given moment. It measures your average glucose over the past 120 days. 

Here are the ranges for A1C results:

• Normal: A1C below 5.7% 

• Prediabetes: A1C between 5.7% and 6.4%

• Diabetes: A1C of 6.5% or higher

Different things can affect your A1C level, like some medications and medical conditions. If this is the case for you, your healthcare team may order other types of tests. If your A1C result is in the diabetes range, you may need diabetes tests to confirm whether you have diabetes. 

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Let’s run through some of those other tests below. 

2. Fasting blood glucose test

A fasting blood glucose test measures the amount of glucose in your blood when you’re fasting. You need to have been fasting for at least 8 hours. That means you haven’t consumed any food or drink (except water). Plan on scheduling this lab test first thing in the morning.

Here are the ranges for fasting glucose results: 

• Normal: less than 100 mg/dL

• Prediabetes: 100 mg/dL to 125 mg/dL

• Diabetes: 126 mg/dL or higher

3. Oral glucose tolerance test

Sometimes, you’ll need a diabetes test that’s a bit more involved — like an oral glucose tolerance test (OGTT). The first part is a fasting blood glucose. It’s also best to do this first thing in the morning, after fasting for at least 8 hours. 

Here’s how the second part of the test works: 

• After your fasting blood glucose, you drink a small bottle of a very sugary drink. Then you wait. 

• After 2 hours, you’ll have another blood draw. And you might have a blood draw after 30 or 60 minutes. 

The results show how well your body is processing sugars. You’ll need to factor in at least 2.5 hours for this test.

OGTT results come back in the following ranges: 

• Normal: less than 140 mg/dL

• Prediabetes: 140 mg/dL to 199 mg/dL

• Diabetes: 200 mg/dL or higher

4. Urine glucose test

Your healthcare team may also order urine testing. This shows if you have glucose in your urine. Glucose in the urine is a sign that there’s too much glucose in the blood and the body is trying to pee it out. 

The test also looks for ketones in the urine. Ketones are a sign that your body isn’t working efficiently to balance its energy needs. It’s not normal to have glucose in urine or large amounts of ketones in urine. Either of these means there’s not enough insulin in the body. 

Urine testing isn’t as accurate as blood testing to help diagnose diabetes. But it can help to figure out which type of diabetes someone has.

5. Random plasma glucose test

A random plasma glucose test measures your blood glucose at any time of the day. It’s a non-fasting test, so you don’t have to stop eating. Healthcare professionals don’t use it to diagnose diabetes. But a random plasma glucose result of 200 mg/dL or higher may mean that you have diabetes. You’ll need more testing to confirm this.

How can you test for diabetes at home?

You can test for prediabetes or diabetes using an FDA-approved, at-home A1C test kit. Some people find at-home A1C testing to be more convenient than going to a laboratory. 

After purchasing a kit from a pharmacy or online, you’ll follow simple how-to instructions for collecting a finger-prick blood sample. Then, you’ll use an at-home reader or place the blood sample in the mail for processing. This varies from kit to kit.

Remember, you’ll need to follow up with a healthcare professional if you receive abnormal results. Do-it-yourself testing doesn’t replace a physical exam and ongoing care from a healthcare professional.

And, know this: An A1C test reflects what your blood sugar levels have been over the past 120 or so days. The test may seem similar to the finger prick test people with diabetes use to check their blood glucose at home. However, it’s very different. A finger prick and glucometer test only tells you what your blood glucose level is at the moment. 

What is the most accurate diabetes test?

A1C testing has become the gold standard for helping diagnose diabetes. It’s the most reliable measure of a person’s glucose over time. If test results show that you have high blood glucose levels, you may need more testing. This will help to figure out if you have prediabetes, Type 1 diabetes or Type 2 diabetes. Here’s what these terms mean:

• Prediabetes is when blood sugar levels are high, but they’re not in the diabetes range. At this point, you can delay and even prevent diabetes with lifestyle changes. 

• Type 1 diabetes is an autoimmune disease in which the body becomes confused and destroys cells that produce insulin. 

• Type 2 diabetes is a metabolic disease in which the body isn’t producing or using insulin properly. 

How can you tell which type of diabetes you have?

Both Type 1 and Type 2 diabetes cause high blood glucose, and so sometimes there can be confusion at diagnosis. In fact, research shows that about 20% of adults with Type 1 diabetes receive a misdiagnosis of Type 2 diabetes. 

So how do you know if you have Type 1 or Type 2 diabetes? There are two specific blood tests that can help: 

1. Anti-insulin antibody testing: The anti-insulin antibody testing measures the levels of antibodies the body has made against cells in the pancreas. 

2. C-peptide testing: The C-peptide testing measures the levels of insulin in the body. 

The diagnosis is usually Type 1 diabetes if the results show positive levels of antibodies and low levels of insulin. This is important information because treatment varies depending on the type of diabetes.

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Written by:

Jewels Doskicz, RN, BA

Jewels Doskicz, RN, is an Arizona-based registered nurse with more than 20 years of hospital-wide clinical nursing experience. She has spent over a decade in medical writing and editing, with a focus on diabetes and autoimmune disease.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Frank Schwalbe, MD

Frank Schwalbe, MD, is an assistant professor of anesthesiology at the Yale School of Medicine. He has practiced anesthesiology for 30 years.

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