Why is the ApoB cholesterol test a better indicator than standard tests?

Why is the ApoB cholesterol test a better indicator than standard tests?

It’s a familiar ritual, regular cholesterol testing. You wake up, skip breakfast — not even coffee — and sit in the exam room sadly, looking up at the ceiling while the phlebotomist inserts a needle into your vein. After a few days, the results appear in your graph.

For decades, primary doctors and cardiologists have focused on two numbers: LDL or low-density lipoproteins, known as “bad cholesterol,” and HDL or high-density lipoproteins, also known as “good cholesterol.” The two numbers are considered major determinants of a patient’s risk of developing cardiovascular disease.

But a growing number of doctors and researchers say it’s time to move beyond this outdated focus on “good” or “bad” cholesterol.

Instead, there is a potentially more accurate marker of heart attack risk: apolipoprotein B (“apoB” for short).

Better test for cholesterol

Research shows that the risk of heart disease depends on the number and type of cholesterol particles in the blood, not on the cholesterol itself. ApoB is the particle that carries cholesterol into the circulation.

Decades of evidence show that measuring the number of apoB molecules in the blood predicts cardiovascular risk much more accurately than a standard lipid panel of good cholesterol and bad cholesterol, but cholesterol guidelines barely acknowledge its existence. Current guidelines only offer this option as an option for certain high-risk patients.

As a result, most patients and even many doctors have no idea that a better cholesterol test exists. “Old habits die hard,” says Anne Marie Navarre, MD, a preventive cardiologist at the University of Texas Southwestern Medical Center in Dallas.

A standard cholesterol panel calculates the total amount Or the concentration of “bad” cholesterol, or LDL, in the blood, in milligrams per deciliter (technically, LDL-C). Since cholesterol is a fatty substance and therefore insoluble in water, it must be carried in small molecules known as lipoproteins.

The test for apoB, a protein found on the outside of LDL-carrying particles, counts number of these lipoprotein molecules in the blood. In addition to LDL, it also picks up other types of cholesterol such as IDL (intermediate-density lipoprotein) and VLDL (very low-density lipoprotein), which carry triglycerides.

Why is this important? As our understanding of heart disease improves, scientists are realizing that apoB molecules are more likely to lodge in the arterial wall, causing it to thicken and eventually form atherosclerotic plaques. Thus, the total number of apoB molecules is more important than the total amount of cholesterol they carry.

ApoB and LDL-C track fairly closely in most people, says Alan Snyderman, a professor of cardiology at McGill University in Montreal. But some people have a “normal” amount of LDL-C, but a high concentration of apoB molecules — a condition called “discordance,” which means they’re more at risk. But traditional cholesterol panels don’t pick up these patients.

“Two people can have exactly the same amount of cholesterol and a completely different number of particles bouncing off the arterial wall,” says Snyderman, who has been researching the lipoprotein ApoB for decades.

Why do people with low cholesterol still have heart attacks

The disagreement may help explain why people with ideal cholesterol numbers still have heart attacks. A widely cited study in 2009 found that more than half of patients admitted to hospital after a heart attack or other cardiovascular disease had “normal” levels of LDL cholesterol, using standard measurement techniques.

Testing for apoB instead of LDL-C could identify people at high risk due to this controversy. “We’re losing people we could have saved,” Snyderman says.

There is a lack of evidence in favor of apoB testing versus traditional LDL-C testing. In the past few years, three large clinical trials (called IMPROVE-IT, FOURIER, and ODYSSEY) have found strongly in favor of apoB as a better predictor of risk than LDL-C.

“There was already a lot of data on apoB,” says Seth Martin, MD, professor of medicine and director of the Advanced Lipid Disorders Program at Johns Hopkins University. “But the guideline recommendations about apoB don’t provide much guidance.” Martin is part of a group of cholesterol experts working with the National Lipid Association to help doctors implement and understand apoB testing.

Currently, U.S. cholesterol guidelines do not suggest that doctors test for apoB in all patients, only those with certain risks, such as those with high triglycerides. As a result, some insurance companies will refuse to pay for the test (I got a $25 one from United Healthcare earlier this year). But some international lipid guidelines support apoB testing.

Salim Virani, co-author of the latest US cholesterol guidelines, issued in 2018, acknowledges that ApoB is a “superior predictor of cardiovascular events compared to LDL cholesterol.” But he says another number on the standard lipid panel effectively conveys the same information: non-HDL cholesterol (total cholesterol minus HDL cholesterol).

“Although doctors can measure ApoB if necessary, non-HDL cholesterol provides free information from a standard lipid panel that doctors can use to stratify risk into what is Higher than LDL cholesterol and beyond.” Dean of Research at the Aga Khan University, Karachi, Pakistan.

Proponents of apoB say it offers more specificity than non-HDL cholesterol — and helps doctors identify individuals who may slip through the cracks with “normal” cholesterol numbers. “It’s not that non-HDL or LDL-C are bad lipid markers — it’s that apoB is better,” says John Wilkins, MD, a professor at Northwestern University Feinberg School of Medicine. . “It’s easy to add to a standard fat pad.”

Wilkins adds that ApoB testing may be especially important in people under 40. He co-authored a 2016 study showing that younger people with high levels of ApoB but normal LDL were at greater risk of developing coronary artery calcification, a relatively advanced stage of heart disease. “There is a very clear relationship between apoB levels and developing the disease later in life,” he says.

“The challenge is that atherosclerosis develops silently for years or decades,” says Martin, of Johns Hopkins University. “If someone develops plaque disease, due to high lipids or other factors, it can be a completely silent process — until the plaque breaks down and they have a heart attack. So it’s important to keep that on your radar even at a young age, especially if you have a specific family history.” “It’s about getting ahead of the curve.”

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