It’s not just about cholesterol. 1 in 5 have high levels of this artery-clogging substance that can lead to heart disease

Sandra Revill Tremulis was a healthy 39-year-old who taught fitness classes and had recently run a marathon when extreme fatigue and chest tingling drove her to see a cardiologist. The doctor discovered she had 95% blockage in one of her coronary arteries and that a heart attack was imminent. And though her own father had died of a heart attack at 50, she was blindsided, believing she was “doing everything right” to stay healthy.

Further bloodwork revealed the culprit: high levels of a particle called lipoprotein(a) in her arteries. That wake-up call, in 2003, prompted her to become an expert on the condition, starting a nonprofit foundation dedicated to research and education (though it dissolved in 2020).

“We need global awareness of lipoprotein(a),” Tremulis tells Fortune. “High lipoprotein(a) impacts one in five globally…And it's not just the individual, it's the families, because each child born to someone with it has a 50% chance of inheriting it.”

According to a solid collection of scientific evidence, high levels of lipoprotein(a)—also known as Lp(a), pronounced “L-P-little-a”—leads to an increased risk of atherosclerotic cardiovascular disease (ASCVD), the group of conditions, such as heart attack and stroke, caused by the buildup of plaque on artery walls. This is especially true for those with familial hypercholesterolemia (FH), an inherited condition that affects the body’s ability to process LDL, or “bad,” cholesterol.

More than 1 billion people worldwide, in fact, are unaware they have at least a 60% increased risk for cardiovascular disease or death due to elevated Lp(a) levels, according to the recently published Lipoprotein(a), a comprehensive book for physicians. "More than 1 billion families worldwide are unaware of their actual risk," Tremulis writes in one of the chapters. "I thought I was rare and an outlier, but, as I discovered, high Lp(a) is not a rare disorder."

So why haven’t you ever heard of lipoprotein(a)? And why isn’t everyone routinely encouraged to have their levels tested?

“The short answer to that is, since we have not had any medication to treat it, there has not been as much interest amongst clinicians as other risk factors,” says Dr. Michael Shapiro, professor of cardiovascular medicine at the Wake Forest University School of Medicine and president of the American Society for Preventive Cardiology.

“Everybody's familiar with LDL cholesterol, so-called bad cholesterol,” he tells Fortune, “because there are measures that people can take, both through lifestyle and with medication, to reduce their LDL cholesterol and reduce the risk for cardiovascular disease.”

In fact, many physicians are still unfamiliar with Lp(a), Shapiro says. But that’s shifting quickly because of major therapeutic developments, with three Lp(a)-lowering drugs currently in their final phase of trials. That will be a game-changer, he says. Because while it’s clear that having high Lp(a) ups one’s risk of cardiovascular disease, what remains unclear is whether lowering that Lp(a) will definitely lower the risk of heart attack and stroke, too.

What is lipoprotein(a)?

Lipoproteins are particles of protein and fat that transport cholesterol within our bodies. Lp(a), mostly produced in the liver, is one form, along with low-density lipoprotein (LDL) and high-density lipoprotein (HDL).

But unlike LDL cholesterol, which can be lowered through diet and other lifestyle changes, Lp(a) is “absolutely genetic,” explains interventional cardiologist Dr. On Chen, director of the lipid management program at the Stony Brook Heart Institute. “Lipoprotein(a) is determined genetically, and there's almost nothing that we can do to modulate that,” he says. “You're going to live and die with the same amount of lipoprotein.” In fact, adult levels of Lp(a) are typically reached by age 5, according to the American College of Cardiology (ACC).

Also unlike cholesterol, Lp(a) is not exactly the topic of frequent conversations. That’s due to its study being a “rapidly evolving” field, according to the National Lipid Association, which released updated guidance for clinicians on how to monitor and treat patients with high Lp(a) earlier this year.

Part of the reason Lp(a) testing has not been as widely adopted as cholesterol measuring, Chen tells Fortune, is because of lingering discrepancy in the medical world about what can be done with the knowledge, given that there is no approved Lp(a)-lowering treatment. (One extreme exception, lipoprotein apheresis, is an efficient but time-consuming way of clearing lipoprotein through “sort of a dialysis for cholesterol,” reserved for only the highest-risk patients, says Chen.)

It means you could have gone to a primary care physician who ordered the test, had trouble finding a lab that offered it, and then found it was not covered by the patient’s insurance. On top of that, if the test was done and Lp(a) levels were found to be high—meaning above 50 mg/dL— the doctor would have likely said there was nothing that could be done about it.

“So [the tests] weren't encouraged,” Chen says, adding that, more recently, "with all the information we have and the fact that we have more tools to use to modulate it…we're more encouraged to use it.”

The National Lipid Association, in its new guidelines, now recommends every adult have Lp(a) levels checked at least once for cardiovascular risk assessment. That follows three other major associations—European Atherosclerosis Society, the European Society of Cardiology, and the Canadian Cardiovascular Society—recommending the same.

While the specific test is not automatically included in most cholesterol screenings, your doctor can order a separate blood test for it. Just don’t be surprised if the test—which can cost anywhere between $25 and $150 depending on where you live—is not covered by your insurance plan.

Why test Lp(a) levels if there’s no treatment yet?

While you cannot change your Lp(a) levels with lifestyle changes as you can with cholesterol levels, you can still lower your risk of cardiovascular disease overall.

That’s particularly important if you have one of several elevated risk factors for high Lp(a), including:

• family history of high Lp(a), early-onset heart disease, familial hypercholesterolemia (FH)

• a personal history of heart attack, stroke, or coronary artery disease before 55 (for men) or before 65 (for women)

• poor leg circulation because of peripheral arterial disease

• aortic stenosis, a narrowing of the valve between the heart’s lower left chamber and the aorta

• being of South Asian descent or Black-African descent, as high Lp(a) numbers disproportionately affect these two racial groups (though people of any race can be affected)

Any of these elevated risk factors could even be a reason to get tested as a young adult, says Chen.

“I think that if I told you when you're 20 that you have an Lp(a) of 200 instead of 50, you'd have said, ‘Oh, my God, I'm going to change my bad lifestyle. I'm going to exercise, because I know that I have a much greater risk of having a heart attack or stroke,’” he notes. "It won't change your Lp(a), but to every given risk, someone with a good lifestyle or a good diet and a good exercise routine will reduce their risk.”

Further, he says, “we’ve learned that when we control cholesterol really aggressively,” a person’s overall stroke and heart attack risk factor goes down, despite the Lp(a) remaining high. Those LDL-lowering treatments might include statins, or newer drugs called PCSK9 inhibitors.

It's why Shapiro is a strong believer in testing every adult, as having a high Lp(a) level puts a person “at least one risk category higher” than they would have been before. Knowing one's levels, he says, would be a signal to be more aggressive about keeping LDL cholesterol and blood pressure down, and just being aware enough to live a heart-healthy life.

He also believes in across-the-board testing because it’s a very common condition. “One in five people have an Lp(a) that’s putting them at risk for atherosclerotic disease or severe stenosis," he says, "but it's hiding in plain sight because it's not being checked."

More on cardiovascular health:

• Will you have a stroke? These 17 factors can be predictors, say new prevention guidelines

• You can lower your cholesterol by up to 25% with diet and exercise. Here’s what to eat more of, and what to cut out

• UPS Store president shares 4 lessons she learned from surviving a ‘widowmaker’ heart attack

This story was originally featured on Fortune.com