High-Density Lipoprotein, also known as HDL, is your "good" cholesterol. It helps to remove the bad cholesterol in our bodies and keeps our blood vessels healthy. But a new study finds HDL cholesterol can sometimes become dysfunctional and lose its cardio-protective properties.

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." explained Cleveland Clinic's Dr. Stanley Hazen, who led the study.

Hazen and his team of researchers 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.

"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," explained Hazen. "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."

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