If you care about your heart, then you’ve probably been told to keep an eye on your cholesterol. For decades, low-density lipoprotein cholesterol (LDL-C) has been the poster child for cardiovascular risk. The higher your LDL-C, the higher your risk of heart attack and stroke. So we measure it, we target it, and we try to lower it.

However, it is little known that LDL-C is just a proxy. What actually damages arteries is not the cholesterol floating around your blood, but the particles that carry it. Each of those particles has, on it’s surface, a protein called apolipoprotein B (apoB). The more apoB particles you have, the more chances they have to burrow into your artery walls and trigger atherosclerosis.

ApoB is, in effect, a headcount of all the atherogenic particles in your blood. For years, evidence has been mounting that it is a better marker of risk than LDL-C. In 2019, European guidelines even stated that apoB was more accurate, easier to measure, and more precise. And yet LDL-C still reigns supreme in clinical practice.

The reason Apob is not used more frequently in current clinical practice is partly inertia. It is also partly habit. And it is partly the argument that LDL-C and apoB are so highly correlated, it makes no practical difference. If you lower one, you lower the other. So many cardiologists and primary care doctors would argue, why bother changing the guidelines?

A new UK Biobank study has put that argument to bed.

Researchers followed nearly 300,000 healthy adults for 11 years. They looked at LDL-C, non-HDL cholesterol, triglycerides and apoB, and tracked how each one related to future heart attacks and strokes.

Yes, LDL-C and apoB were highly correlated. But the correlation was not perfect. At any given LDL-C level, individual apoB levels varied widely. Two people could have the same LDL-C, but one might have far more apoB particles quietly driving up their cardiovascular risk.

Across every LDL-C or non-HDL-C level, people with higher apoB levels had significantly more cardiovascular events. ApoB gave extra risk information that LDL-C or non-HDL-C simply missed.

When the researchers ran adjusted statistical models, apoB consistently came out on top as the stronger predictor of risk. LDL-C added no meaningful information once apoB was taken into account.

Some guidelines only recommend testing apoB if your triglycerides are high. The idea is that apoB might only be useful in those cases, when cholesterol particles are small and harder to measure accurately using standard tests. But this study found no support for that.

In fact, apoB was consistently useful regardless of triglyceride levels. Even when triglycerides were taken into account, apoB still gave meaningful extra information about risk. The reverse wasn’t true. Once you knew someone’s apoB, their triglyceride level didn’t add much.

This suggests apoB is giving us more useful insight, across the board, not just in people with high triglycerides.

Because in clinical practice, we are treating individual patients, not population averages. Knowing your apoB level helps tailor your treatment far more accurately. Without it, there is too much guesswork. Two patients with the same LDL-C could have very different numbers of atherogenic particles, and very different risk.

We now have safe and powerful therapies, from statins to PCSK9 inhibitors. But they are costly and need to be used wisely. ApoB is the best tool we have to target those therapies to the right people.

One argument that is frequently given is cost. But measuring apoB is inexpensive. In the US, it would raise lipid testing costs by about 1 percent. And in reality, once apoB is used, there is little need to keep measuring LDL-C or non-HDL-C, so the total cost of care need not rise.

Another barrier is familiarity. Doctors and labs are used to ordering LDL-C. Changing habits takes time. But with evidence like this, the argument for change is becoming hard to ignore.

ApoB is the best available measure of atherosclerotic risk. LDL-C and non-HDL-C are imperfect stand-ins. If you want the most accurate picture of your cardiovascular risk, you should know your apoB.

If you are already on treatment, it is the best way to know if your therapy is working. If you are not yet on treatment but considering it, it can help you and your doctor make a better-informed decision.

If guidelines and clinical practice catch up to the evidence, we will prevent more heart attacks and strokes. And that, surely, is the whole point.