The apoB test could detect the risk of heart attack and stroke better than LDL

When assessing the risk of heart disease, doctors typically rely on LDL cholesterol analysis, known as "bad cholesterol". However, a recent study by researchers at Northwestern Medicine suggests that this measurement may not capture the full picture, and that another test — apolipoprotein B (apoB) — could more accurately identify people who need more aggressive treatment to prevent heart attacks and strokes.

The difference between LDL and apoB

Cholesterol travels through the bloodstream via particles called lipoproteins, some of which can contribute to the formation of atherosclerotic plaques that narrow the arteries. Currently, doctors primarily use two values to assess risk: LDL cholesterol, which estimates the amount of cholesterol carried by particles considered harmful, and non-HDL cholesterol, which encompasses several types of particles that can promote deposits.

Apolipoprotein B takes a different approach: rather than measuring the amount of cholesterol, it counts the number of particles capable of causing these deposits. "Research strongly shows that apolipoprotein B is more effective at identifying people at risk because it counts the total number of harmful particles in the blood," explained Ciaran Kohli-Lynch, lead author of the study and assistant professor of preventive medicine at Northwestern University Feinberg School of Medicine. In practice, two people may have the same LDL value but a different number of apoB particles, which translates to a different level of cardiovascular risk.

How the study was conducted

The research, published in the journal JAMA, was based on a computer model that simulated health outcomes for approximately 250,000 adults in the United States who were eligible for statin treatment but did not already have cardiovascular disease.

The model compared three decision-making strategies for intensifying treatment:

• using LDL cholesterol, with a target below 100 mg/dl;
• using non-HDL cholesterol, with a target below 118 mg/dl;
• using apoB, with a target below 78.7 mg/dl.

When patients failed to reach their target, treatment was intensified with stronger statins and, where necessary, with the medication ezetimibe. The researchers tracked the long-term number of heart attacks and strokes, life expectancy, quality of life, and healthcare costs.

Better outcomes with apoB

The apoB-based strategy outperformed those based on LDL or non-HDL. According to the authors, using apoB to guide treatment could prevent more cardiovascular events than current practice and would offer a favourable cost-benefit ratio for healthcare systems.

"We found that testing apoB to guide the intensification of cholesterol-lowering medication would prevent more heart attacks and strokes than current practice," said Kohli-Lynch. The researchers assert that this is the first large-scale analysis to demonstrate that using apoB to determine treatment is effective both medically and economically.

Why the test is not yet widely used

Although the evidence in favour of apoB continues to grow, the test is not routinely used for most patients, primarily because it typically requires an additional blood draw beyond standard cholesterol tests, which can increase costs for the patient.

"Our study asked the question: is it worth spending extra money to use apoB instead of LDL to guide treatment intensification?" said Kohli-Lynch. The researchers conclude that, in many situations, the additional information provided by apoB could justify this cost.

The context of new medical guidelines

The study comes at a time when doctors have more cholesterol-lowering treatment options available than ever before. Earlier this year, the American Heart Association and other medical organisations published updated guidelines on cholesterol management, placing greater emphasis on the earlier identification of high-risk individuals. In this context, the central question for specialists is how to most accurately identify the patients who would benefit most from intensive treatment.

What this means for patients

The study's findings do not render LDL testing obsolete — it remains an important indicator, widely used in cardiovascular risk assessment. The researchers' message, however, is that LDL does not always capture the full picture of risk.

For certain individuals — particularly those with elevated cardiovascular risk, multiple risk factors, or inconclusive results — measuring apoB could provide additional information that is useful in selecting the right treatment. The decision to request this test or to modify treatment should be made together with a doctor, taking into account each patient's individual medical history and risk profile.