CHICAGO (Reuters) - New tests that measure individual particles of LDL -- so-called bad cholesterol -- may one day help doctors predict which patients will develop heart problems, but not quite yet, U.S. researchers said on Monday.

Doctors routinely measure low-density lipoprotein, or LDL, as one of many risk factors used to calculate a person's heart disease risks.

But several companies including Quest Diagnostics Inc and privately held Atherotech Inc, LipoScience Inc and Berkeley HeartLab Inc have developed more refined tests that measure the size and concentration of individual LDL particles.

Smaller LDL particles are thought to be more dangerous than larger ones because they can easily become embedded in artery walls, forming clots that may break off and cause a heart attack or stroke.

And several studies have found a variety of such LDL particle tests might predict heart complications.

Dr. Ethan Balk of Tufts Medical Center in Boston and colleagues looked at data from 24 published studies that found a link between LDL particle concentrations and heart disease.

In all of the studies, they found the higher the LDL particle number, the higher the risk for heart disease, regardless of the levels of other fats, such as high-density lipoprotein or HDL, the so-called good cholesterol considered protective against heart disease.

Nevertheless, the studies have not yet proven that tests measuring LDL concentrations are any better than traditional assessments, the researchers wrote in the Annals of Internal Medicine.

The study was funded by the Agency for Healthcare Research and Quality.

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