Who should have their ApoB measured?

ApoB is a protein found on every harmful cholesterol particle. Measuring ApoB directly counts those particles. Standard LDL cholesterol only measures the total weight of cholesterol, which is not the same thing. Population research shows that at an LDL of 100 mg/dL, the corresponding ApoB can range from 66 to 99 mg/dL. Someone with a high ApoB alongside a 'normal' LDL is carrying more harmful particles. That risk stays hidden if you only measure LDL.

People with excess weight, diabetes, or elevated blood fats benefit most from measurement. In those groups, ApoB most often diverges markedly from what LDL indicates. Guidelines recommend measuring ApoB in cases of elevated blood fats, but research shows that people without known risk factors can also have a strikingly high ApoB. The threshold for testing has probably been drawn too narrowly.

Children with familial hypercholesterolaemia (an inherited condition in which LDL is strongly elevated from birth) form a separate group. In one small study of children with genetically confirmed familial hypercholesterolaemia, more than 34 percent had an unfavourable ratio between ApoB and the protective protein ApoA. That ratio, together with vascular abnormalities, was sometimes a reason to start statins earlier.

Are you already taking cholesterol-lowering medication? ApoB can then help assess whether the treatment is working well enough. Especially with persistently elevated blood fats, LDL underestimates the risk. ApoB shows whether the actual number of harmful particles has fallen sufficiently.

Women around and after the menopause also benefit particularly from measurement. After menopause, ApoB rises and the variation between women increases. Twin research shows that lifestyle plays a relatively larger role before menopause, but that shifts afterwards. Measuring around the time of menopause helps determine whether your risk has changed.