Apolipoprotein B (ApoB)

Apolipoprotein B (ApoB) is the single structural protein present on every atherogenic lipoprotein particle, one copy per LDL, VLDL, IDL, and Lp(a) particle, so an ApoB test counts the actual number of particles capable of depositing cholesterol in artery walls, rather than estimating cholesterol mass the way a standard LDL-C test does. The claim, increasingly adopted in cardiology guidelines: ApoB predicts atherosclerotic cardiovascular disease (ASCVD) better than LDL-C, especially when LDL-C and particle number are discordant, as commonly happens in people with insulin resistance, high triglycerides, or metabolic syndrome.

An analysis combining UK Biobank (primary prevention) and the FOURIER and IMPROVE-IT trial cohorts (secondary prevention, PCSK9 inhibitor and ezetimibe trials) found ApoB was the only lipid measure independently associated with incident myocardial infarction across both cohorts, with the risk captured by ApoB independent of whether the underlying lipid was cholesterol or triglycerides [1]. A 2024 JACC study of excess ApoB, the ApoB level above what LDL-C alone would predict, found a dose-dependent association with myocardial infarction and ASCVD across a median 9.6-year follow-up in both sexes, with hazard ratios up to 1.52 (men) and 1.75 (women) at the highest excess-ApoB category compared to the lowest, and this held across the entire LDL-C spectrum, meaning even people with normal LDL-C but high ApoB carried excess risk [2]. Mendelian randomization studies, which use genetic variants as natural experiments to infer causation, have separately supported ApoB-containing particle number, not cholesterol content per se, as the causal driver of atherosclerosis.

How to measure it: a standard non-fasting blood draw processed by immunoturbidimetric or nephelometric assay, reported in mg/dL or g/L [3]. Unlike LDL-C, which is often calculated rather than directly measured via the Friedewald equation, which becomes unreliable at high triglycerides, ApoB is measured directly and is not affected by triglyceride levels, which is part of its appeal in patients with metabolic syndrome or diabetes [4].

How to intervene on it: statins, ezetimibe, and PCSK9 inhibitors all lower ApoB, generally tracking their LDL-C-lowering effects, though the 2021 Canadian Cardiovascular Society guideline and a growing number of cardiology societies now recommend using ApoB directly as a treatment target (under 0.7 g/L for very high-risk patients) rather than inferring particle number from cholesterol content [3].

Critics note ApoB testing is not yet universally available or reimbursed everywhere, and most large outcome trials for lipid-lowering drugs were originally designed and reported around LDL-C, so the outcome evidence base for ApoB as a treatment target, while strong on prediction, is still catching up on treat-to-target trial data specifically powered around ApoB thresholds rather than LDL-C thresholds [4]. Bryan Johnson's Blueprint protocol reports ApoB alongside LDL-C on its public dashboard as a routine panel biomarker, an n=1 example of the dual-testing approach rather than trial evidence [5][6].

The plain takeaway: ApoB counts the actual particles that cause atherosclerosis and outperforms LDL-C at predicting heart attack risk, particularly in people with high triglycerides or metabolic syndrome, and cardiology guidelines increasingly recommend testing it directly rather than relying on LDL-C alone.