Apolipoprotein B (Apo B)

Apolipoprotein B (Apo B) is the structural protein on LDL, VLDL, IDL, and Lp(a) particles — one Apo B molecule per particle. Because each atherogenic particle carries exactly one Apo B, the measurement directly reflects the number of atherogenic particles in circulation. Many lipidologists consider Apo B a more accurate predictor of cardiovascular events than LDL cholesterol.

Elevated Apo B indicates a higher number of atherogenic lipoprotein particles, which increases the probability of arterial wall penetration and plaque formation. Notably, Apo B can be elevated even when standard LDL-C is normal (concordance/discordance), making it particularly informative for risk stratification in metabolically complex individuals.

Individuals with low body fat and high fitness levels can still carry elevated Apo B — a pattern sometimes described in lean mass hyper-responders, particularly on low-carbohydrate or ketogenic diets. Apo B provides a particle-level view of atherogenic risk that is not captured by standard cholesterol measurements alone.