Blood Protein Ups Heart Risk

Sept. 19, 2006 -- It's long been suspected of aiding and abetting bad cholesterol. Now medical detectives looking for a heart disease culprit say very high levels of a blood protein called lipoprotein(a) nearly double heart disease risk.

This dangerous substance helps cholesterol stick to the walls of your arteries. But it's been hard to make a case against it -- mainly because there's been no reliable way to measure the protein.

But technology -- and researchers at Brigham and Women's Hospital -- finally has caught up with lipoprotein(a).

The researchers did it by using a state-of-the-art lipoprotein(a) test to analyze frozen blood samples collected 10 years ago from nearly 28,000 middle-aged women in the Women's Health Study. The women were healthy at the start of the study.

As it turns out, most of us have little to worry about from lipoprotein(a). Only very high levels of the protein are linked to heart disease. In fact, the study suggests it is dangerous only at levels more than twice as high as those previously thought harmful.

However, when lipoprotein(a) levels are high, it's bad news. One in 10 women has a lipoprotein(a) level of 65.5 mg/dL or greater. Those women have a 66% higher risk of heart disease.

One in 100 women has a level of 130.7 mg/dL or greater. That doubles a woman's risk of heart disease.

Lipoprotein(a) doesn't do its dirty work alone. It teams up with LDL cholesterolLDL cholesterol -- the bad cholesterol.

The link between lipoprotein(a) and heart disease is strongest among women with above-normal LDL cholesterol levels, find Jacqueline Suk Danik, MD, MPH, and colleagues.

Because lipoprotein(a) showed increased risk only at very high levels, and because there is no proof yet that lowering lipoprotein(a) levels lowers heart risk, the researchers don't advise routine testing.

"Determination of lipoprotein(a) levels should … be reserved for high-risk subsets of the population, such as individuals with premature [heart attacks] who have otherwise normal risk profiles or are at particularly high risk because of circumstances such as [inherited high cholesterolhigh cholesterol]," Danik and colleagues suggest.

The study appears in the Sept. 20 issue of The Journal of the American Medical Association.