ApoB versus LDL cholesterol: counting particles instead of cargo

LDL cholesterol and ApoB usually agree, and the interesting cases are the ones where they do not. Knowing which number your report actually gave you — and how it was arrived at — is most of the work.

The difference in one paragraph

LDL cholesterol measures the cholesterol carried inside LDL particles. ApoB counts the particles: each atherogenic particle carries exactly one apolipoprotein B molecule, so an ApoB concentration is a particle count in all but name. LDL-P, measured by NMR or ion mobility, counts the same thing a different way.

Established clinical use They diverge when particles are unusually cholesterol-poor or cholesterol-rich. Someone with many small dense particles can carry a reassuring LDL-C and a high ApoB — more particles, less cargo in each. Where the two disagree, meta-analysis has found ApoB the better marker of risk.² That discordant pattern travels with insulin resistance and high triglycerides, which makes it relevant to a good part of this audience.

Which LDL number did your lab actually give you?

Established clinical use Most LDL-C is not measured at all — it is calculated. The classic Friedewald equation derives it from total cholesterol, HDL and triglycerides, and it is unreliable when triglycerides are high, which is the app's own note on this marker. The Martin-Hopkins method uses an adjustable factor instead of a fixed one and misclassifies substantially fewer people, particularly at low LDL and high triglycerides.¹ Direct LDL assays measure it, and are less common.

The registry tracks all three because they are not interchangeable, and because the case where they disagree most — high triglycerides — is exactly the case where someone is most likely to be looking. If your LDL-C came from Friedewald with high triglycerides, it is not a usable number, and that is a laboratory fact rather than an opinion.

Off-label or community practice Non-HDL cholesterol sidesteps the calculation problem: it is total cholesterol minus HDL, requires no fast and no equation, and captures cholesterol in all atherogenic particles. It is the cheapest sensible answer to "my LDL number looks odd", and it sits in guideline practice alongside ApoB.³

Particle counts do not travel between platforms

Established clinical use LDL-P measured by NMR and LDL-P measured by ion mobility are not interchangeable, and the app's registry says so explicitly: do not trend across platforms. The absolute numbers differ, so a change of laboratory can produce an apparent change in you that is entirely a change of method.

ApoB is the more portable of the two. It is a standardised immunoassay, widely available, inexpensive, and does not require a fast — which is a large part of why it has been gaining ground as the preferred single measure of atherogenic burden.³

What moves these on protocol

Off-label or community practice The lipid effects of androgens are dose- and route-dependent and are not uniform: oral 17-alpha-alkylated compounds are the ones associated with the sharpest HDL suppression, while injectable testosterone at replacement doses has a more modest effect. What the community reports and what the literature describes agree that the effect is real and that it is worth measuring rather than assuming.

GLP-1 receptor agonists generally move lipids favourably, largely through weight loss. A lipid panel that improves on semaglutide or tirzepatide is expected. Neither direction is a reason to change anything on your own — an atherogenic burden that is genuinely elevated is a long-horizon cardiovascular question, and the person to have it with is a clinician who can see your whole risk picture rather than one line of a panel.

What the app records for this marker

Questions people actually ask

Should I ask for ApoB instead of a standard lipid panel?

ApoB is inexpensive, standardised, needs no fast and answers the particle question directly, so asking for it alongside a standard panel is reasonable. Whether it changes anything about your management is a clinical question — but it is the number least likely to mislead you, and the one least sensitive to how your lab calculates LDL.

My LDL is fine but my ApoB is high. What does that mean?

It means your particles are carrying less cholesterol each, so you have more of them than the LDL number implies. That discordant pattern is the reason ApoB is measured at all, and it travels with insulin resistance and high triglycerides. It is worth showing to a clinician rather than reconciling yourself — the discordance is the finding.

Does the converter handle mmol/L?

Yes, for LDL and non-HDL cholesterol — mmol/L times 38.67 gives mg/dL, using the app's own factor. ApoB converts from g/L. LDL-P is reported in nmol/L only, and the app refuses to convert particle counts between platforms because there is no valid conversion.

Sources

Every claim above that is not a definition is either labelled by evidence tier or carries a numbered reference to one of these.

1. Martin SS et al., Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels, JAMA 310(19):2061 (2013) The Martin-Hopkins method, and where Friedewald misclassifies — particularly at low LDL and high triglycerides.
2. Sniderman AD et al., A meta-analysis of LDL-C, non-HDL-C and apoB as markers of cardiovascular risk, Circ Cardiovasc Qual Outcomes 4(3):337 (2011) Head-to-head comparison of the three measures as risk markers.
3. Grundy SM et al., 2018 AHA/ACC Guideline on the Management of Blood Cholesterol Where ApoB and non-HDL cholesterol sit in guideline practice, and the thresholds used.