CLEVELAND, Ohio -

As if cholesterol wasn't confusing enough, now there's this. 

It seems the "good" cholesterol that we've all heard about, sometimes isn't so good after all.

High-density lipoprotein, known as HDL, is what doctors typically refer to as our “good" cholesterol.  That's because it helps to remove the "bad" cholesterol in our bodies and keep our blood vessels healthy.

But a new study led by Cleveland Clinic’s Dr. Stanley Hazen finds HDL cholesterol can sometimes become dysfunctional and lose its cardio-protective properties.  So what causes "good" cholesterol to go bad?  The change occurs when HDL is lifted from the bloodstream and latches onto the artery wall.

"This paradox we are now seeing is because HDL in the artery wall is different than HDL in the bloodstream," said Hazen.

Hazen and his team tested the blood of more than 600 people.  They found that when HDL is moving throughout our bloodstream, it does a lot of good, but when it latches to the artery wall, something bad happens.  A protein known as apoA1, which normally gives HDL its cardio-protective qualities, is oxidized in the artery wall.

When this happens, it strips the HDL of its good qualities and causes it to contribute to the development of coronary artery disease.

Hazen said the hope now is to find ways to stop this process in its tracks.

"It’s a big advance in terms of first, being able to identify people who are at risk, who we didn’t understand were at risk, and also a way of monitoring the HDL raising efforts by so many drug companies that have been failing.  They haven’t been able to monitor what’s been happening in the artery wall, they’re monitoring what is happening in the bloodstream, which we now realize is not reflecting what is happening in the artery wall," said Hazen.

Complete findings for this study are in the journal Nature Medicine.

To learn more about "good" and "bad" cholesterol, click here.