Who should have their ApoB measured?

ApoB (apolipoprotein B) is a protein found on every single LDL particle. By measuring ApoB, you are directly counting the number of harmful cholesterol particles, whereas the standard LDL-cholesterol test only measures the total weight of cholesterol carried inside those particles. These two things are not the same. Population research shows that at an LDL-cholesterol level of 100 mg/dL, the corresponding ApoB value ranges from 66 to 99 mg/dL -- a difference of more than 30 mg/dL among people with apparently similar cholesterol values. Someone with a high ApoB alongside a 'normal' LDL-cholesterol is carrying more particles and therefore has a higher risk that currently goes undetected.

People with metabolic risk factors have the most to gain from an ApoB measurement. In the presence of excess weight, diabetes, or elevated triglycerides, ApoB more often and more substantially diverges from what LDL-cholesterol indicates. Current guidelines recommend ApoB testing mainly in the case of elevated triglycerides, but research shows that even metabolically healthy people without known risk factors can have a notably high ApoB. This suggests that the threshold for measuring ApoB may have been drawn too narrowly.

Children with familial hypercholesterolaemia (an inherited condition in which LDL-cholesterol is markedly elevated from birth) form a distinct group for whom ApoB is particularly useful. In a study of children with genetically confirmed familial hypercholesterolaemia, more than 34 percent had an elevated ratio of ApoB to ApoA (the protective protein on HDL). This ratio, combined with abnormalities of the vessel wall detected on ultrasound, was used as a reason to start statin treatment earlier.

In people who are already taking statins, ApoB can serve as an additional measurement to assess whether treatment is adequate. This is especially relevant when triglycerides remain persistently elevated, because in that situation the small, dense LDL particles pose an extra risk that LDL-cholesterol underestimates. The ApoB value then shows whether the actual number of harmful particles has fallen sufficiently.

Women around and after the menopause form a group that may particularly benefit from an ApoB measurement. After menopause, ApoB levels rise and variation between women increases. Before the menopause, lifestyle factors (such as diet) still play a relatively large role in determining the ApoB value; afterwards, that influence shifts. This makes testing around the time of the transition worthwhile in order to determine whether cardiovascular risk has changed.