ApoB or LDL particle number: which test is better?
ApoB, for almost everyone. Both try to count the particles that build plaque. ApoB counts all of them with one protein each, on a test that’s standardized and doesn’t need fasting. Particle tests sort the particles by size with methods like NMR, and the 2026 US guideline says most of what they report doesn’t improve risk or treatment beyond a standard panel plus ApoB or Lp(a).
What we’d do
Ask for ApoB. If you already have an LDL particle number from an NMR test, it’s telling you roughly the same thing, and you don’t need both. Spend your attention on what moves the count, like saturated fat and the protein on your plate, since the size mix of your particles adds little once you know how many there are.
Two ways to count
| ApoB | LDL particle number | |
|---|---|---|
| What it counts | Every particle that can build plaque: VLDL, IDL, LDL and Lp(a), one ApoB each | LDL particles, sorted by size |
| How | An antibody test on the same lab machines as a standard panel | Specialty methods such as NMR or ion mobility |
| Standardized | Yes, against an international reference | The guideline points to a lack of standardization across assays |
| In the 2026 guideline | Class 2a once LDL goals are met on treatment, 2b for risk before treatment | Limit to cases where it would change the plan |
The National Lipid Association says ApoB tests run on the high-throughput machines labs already use for cholesterol, so “the cost of performing the test is low and its accuracy is high”. In the College of American Pathologists survey, most ApoB tests came within 4 mg/dL of the true value. ApoB tests have been around since the 1980s.
Does particle size matter?
This is the real argument behind particle tests. Some researchers think small, dense LDL particles are worse than large ones, so knowing the size mix should help. A 2019 feeding trial even found that meat and saturated fat raised ApoB mostly by adding large LDL particles, and its authors pointed out that large LDL hasn’t been tied to heart disease in several cohorts.
The biggest study on particle kinds points the other way. In UK Biobank and two drug trials, Marston and colleagues looked at 429,959 people. Once they knew how many ApoB particles someone had, it made no difference to heart attack risk whether those particles were LDL or the triglyceride-rich kind, or how much cholesterol they held. Risk “was best captured by the number” of particles, they wrote. That study compared kinds of particles, not LDL sizes, but it points the same way.
It’s like counting cars on a bridge. A toll counter that clicks once per car gives you the number you need, and a camera that sorts them into sedans and SUVs adds detail that doesn’t change how crowded the bridge is.
What the guideline says
The 2026 guideline lists the reasons it holds back on particle tests: “lack of standardization across assays, the potential for information overload, and uncertainty as to which patients are most likely to benefit”. It says they “should be limited to scenarios where availability of such information is likely to meaningfully change the treatment plan”. Who should get an ApoB test? covers when ApoB helps most.
5 sources
- Blumenthal RS, Morris PB, Gaudino M and others, 2026 ACC/AHA guideline on the management of dyslipidemia, JACC, 2026doi.org
- The same guideline, full text, Circulation, 2026api.iscpcardio.org
- Soffer DE, Marston NA, Maki KC and others, Role of apolipoprotein B in the clinical management of cardiovascular risk in adults: an Expert Clinical Consensus from the National Lipid Association, Journal of Clinical Lipidology, 2024pmc.ncbi.nlm.nih.gov
- Marston NA and others, Association of apolipoprotein B-containing lipoproteins and risk of myocardial infarction in individuals with and without atherosclerosis, JAMA Cardiology, 2022pubmed.ncbi.nlm.nih.gov
- Bergeron N and others, red meat, white meat and plant protein on high and low saturated fat diets, a feeding trial in 113 adults, American Journal of Clinical Nutrition, 2019pmc.ncbi.nlm.nih.gov
