ApoB: The Cholesterol Number Most Panels Skip

A standard lipid panel reports total cholesterol, HDL, LDL and triglycerides. LDL cholesterol is the number most people and most doctors treat as the bad one, and it is a reasonable proxy. But it measures the wrong thing for the question we actually care about. It measures how much cholesterol is being carried. ApoB measures how many particles are carrying it.

Cargo versus trucks

Cholesterol does not float freely in the blood. It travels packed inside lipoprotein particles, and every particle that can cause plaque, LDL, VLDL and their remnants, carries one molecule of apolipoprotein B on its surface. Count ApoB and you have counted the trucks on the road.

LDL cholesterol, by contrast, weighs the cargo. Two people can have the same LDL cholesterol of 110 while one carries it in a smaller number of large, well packed particles and the other in a much larger number of small, half empty ones. The second person has more trucks on the road and more risk, and the standard panel cannot tell them apart.

Why particles matter

Plaque starts when a particle slips through the lining of the artery and gets stuck in the wall, where it is oxidized and draws in immune cells. The chance of that happening scales with how many particles are passing by, over how many years. The more particles traveling through the arteries, the greater the chance one gets stuck to the wall. That is the whole picture, and it is why ApoB tracks heart attack risk more closely than LDL cholesterol does, especially when the two numbers disagree.

The mismatch is most common in exactly the people who look fine on a basic panel: someone with high triglycerides, insulin resistance, a larger waist or type 2 diabetes. Their LDL cholesterol often sits in the normal range while their particle count is high. "Everything looks normal" and a first heart attack in the 50s are closer together than they should be.

What we do with it

Adding ApoB and ApoA1 to a lipid panel costs about $30 cash. ApoA1 is the protein on HDL particles, so the pair gives a particle level view of both sides.

European guidelines set ApoB goals of under 100 milligrams per deciliter at moderate risk, under 80 at high risk, and under 65 for very high risk, such as someone with established plaque. When it is high, the levers come in a familiar order: less saturated fat, less refined carbohydrate and alcohol, more fiber, more muscle, and medication when lifestyle does not get it there or when the risk is already high. The difference is that we are watching the number that tracks the risk most closely.

Unfortunately it is very common for primary care to check a basic lipid panel and stop there. If nobody has looked at this for you, it's worth a conversation.

This article is educational and is not medical advice.

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