Recent research suggests that more people should be screened for a protein called apoB. A growing number of doctors agree.

"Bad," or LDL, cholesterol is a major risk factor for heart disease and most people are screened for it as part of their yearly physicals.

There`s another marker in the blood that may be a better predictor of heart disease risk, a recent large review suggests. But it`s not part of routine blood testing.

Apolipoprotein B (apoB) is a protein that attaches to harmful fat particles in the blood. The apoB protein is found on the surface of harmful lipoproteins like low density lipoprotein, or LDL, that contribute to heart disease. Since each one of the harmful particles contains one apoB molecule, testing for it essentially captures the overall number of harmful plaque-producing compounds.

Doctors typically keep a close eye on LDL as a main clue whether someone is at risk of developing heart disease. If it`s elevated, they may recommend lifestyle changes or starting medication to lower it.

Cholesterol is a waxy, fat-like substance the body uses to build cells and make hormones such as testosterone and estrogen. A blood lipid panel typically provides insight into the total level of cholesterol in the blood, including LDL, very low-density lipoprotein (VLDL) and high-density lipoprotein (HDL). The blood test also checks for triglycerides, another type of fat in the blood that can contribute to heart disease.

LDL and VLDL can get stuck in the walls of an artery, ultimately causing narrowing of the vessel and contributing to heart disease, said Dr. Ann Marie Navar, a preventive cardiologist at UT Southwestern Medical Center in Dallas.

"Cholesterol isn`t dissolved in the blood like sugar and sweet tea. It`s packaged up in these things called lipoproteins," said Navar.

The problem is, a normal LDL level may not necessarily mean you`re in the clear. Some people may have undetected elevated apoB - a phenomenon called discordance. Factors such as being overweight or having diabetes or high triglyceride levels make that mismatch between normal LDL and elevated apoB more likely.

The American Heart Association`s current guidelines don`t recommend routine testing for apoB as part of cholesterol screening, except for some patients with high triglycerides.

Navar, however, believes all adults should be screened for it, and she routinely checks apoB in her patients.

Dr. Samia Mora, a cardiologist and the director of the Center for Lipid Metabolomics at Brigham and Women`s Hospital, recommends testing for apoB at least once to make sure it`s in line with LDL screening results.

How is apoB tested?

Heart disease is the No. 1 cause of death for men and women in the U.S.

According to Dr. Thomas Dayspring, a fellow of the National Lipid Association and a renowned cholesterol expert, hardening of the arteries caused by a buildup of plaque-producing particles is best evaluated using the apoB test.

"ApoB is by far the best metric that every human should get tested for when they do their cardiovascular risk assessments," Dayspring said last fall during an appearance on the "Proof with Simon Hill" podcast.

An apoB test looks directly at the number of artery-clogging particles in the blood. "LDL cholesterol is telling me how much cholesterol is carried by the LDL particles, and apoB is telling me how many of the LDL particles I have," said Mora.

Dr. Jeffrey Berger, a preventive cardiologist at NYU Langone, said "apoB offers a practical and comprehensive way to basically assess cholesterol burden," which is involved in the accumulation of bad cholesterol and plaque formation.

However, less than 1% of adults in the U.S. have been tested for the blood protein, according to a 2024 study sponsored by drugmaker Regeneron and published in The American Journal of Preventive Cardiology.

ApoB testing is hot among health influencers and increasingly touted in the commercial blood testing market. Recently, the Sweetgreen salad chain - which has tied itself to anti-seed-oil influencers - launched a collaboration with the testing company Function Health and is promoting apoB screening along with its menus.

Dr. Michael Shapiro, a preventive cardiologist and the chair of the American Heart Association Council on Lipidology, Lipoprotein, Metabolism & Thrombosis, said that he typically uses an apoB test in select patients.

"I think the best use case is when you`re treating somebody with lipid-lowering therapy," he said, referring to medications such as statins, which are taken to lower cholesterol. "Maybe you`ve gotten them to the LDL cholesterol you were trying to get them to and now you want to adjudicate whether they`ve really gotten to the goal that you want them to get."

In some cases, insurance may cover the test. If not, it typically costs around $70 at a lab.

There aren`t clear guidelines for what target apoB levels should be. In healthy people, apoB values less than 90 mg/dL are typically considered acceptable, with some saying lower targets closer to 70 mg/dL may be more optimal for preventing heart disease.

For Navar, the real concern is that people aren`t getting their cholesterol checked at all. Almost 25% of eligible adults haven`t been screened in the last five years, according to research from Johns Hopkins University.