Which Test Best Spots Diabetes?

Prediabetes and diabetes identified more often by OGTT than HbA1c

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) There are many tests used to diagnose prediabetes and type 2 diabetes. These same tests can also give doctors a picture of patients' blood sugar control and risk of heart problems. But which tests work best?

The oral glucose tolerance test (OGTT) spotted more people with prediabetes and type 2 diabetes, compared to HbA1c (a measure of blood sugar over time).

"Get tested for diabetes if you're overweight or over 45."

In their recent study, Stefano del Prato, MD, of the University of Pisa in Italy, and colleagues wanted to see how well HbA1c and OGTT could spot people with different causes of diabetes and risks of heart problems.

People with type 2 diabetes have high levels of sugar, or glucose, in the blood. Before developing type 2 diabetes, people almost always have prediabetes - a condition in which blood sugar levels are higher than normal but not high enough to be called diabetes.

HbA1c is a test that shows the average amount of sugar in the blood over a 3-month period. The test is not only used to diagnose prediabetes and diabetes, but also to see how well patients are controlling their diabetes.

OGTT is another tool commonly used to diagnose prediabetes and diabetes. This test measures how well the body uses glucose.

In the study, results from OGTT showed that 42 percent of participants had prediabetes and 15 percent had type 2 diabetes. In comparison, HbA1c showed that 38 percent had prediabetes and 11 percent had type 2 diabetes.

Of those patients diagnosed with prediabetes, 54 percent tested positive for prediabetes in both tests. Of those diagnosed with type 2 diabetes, 44 percent tested positive for type 2 diabetes in both tests.

People who had prediabetes according to both tests were more resistant to insulin and produced less insulin than people who had normal blood sugar according to both tests.

Insulin is a natural hormone that helps control blood sugar levels. The hormone takes sugar from the blood so it can be used as energy by the body.

If someone is insulin resistant, the body does not respond to insulin, causing sugar to build up in the blood and eventually leading to prediabetes and diabetes. Blood sugar also builds up if a person's body does not produce enough insulin.

The study's authors concluded that HbA1c spotted a smaller amount of people with prediabetes and an even smaller amount of people with type 2 diabetes, compared to OGTT.

There was no difference in insulin resistance, insulin production or risk of heart problems.

People who were shown to have prediabetes or type 2 diabetes by both tests had a worse metabolic profile. That is, their body's ability to use sugar as energy was worse than those diagnosed in just one test.

The study - which included 844 people - was published August 21 in Diabetes Care, a journal of the American Diabetes Association. 

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Review Date: 
August 28, 2012
Last Updated:
September 6, 2012