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LDL Particle Number (LDL-P)

The number of LDL particles in your blood. Some clinicians use it next to LDL cholesterol to see how many cholesterol-carrying particles you have.

AI-verified against cited sources. Awaiting expert reviewAlso called LDL-PLOINC 54434-6

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What it is

LDL cholesterol (LDL-C) tells you how much cholesterol is inside your LDL particles. LDL particle number (LDL-P) counts the particles themselves. Particles carry different amounts of cholesterol, so two people with the same LDL-C can have different particle counts. Labcorp and Mayo Clinic Laboratories measure LDL-P with nuclear magnetic resonance (NMR), and Quest offers both NMR and ion mobility. The methods count a little differently, so use the same lab and method when you compare results over time.

Why it matters

LDL particles carry cholesterol into artery walls, where plaque builds up, so more particles is linked to a higher chance of heart attack and stroke over many years. LDL-C and LDL-P usually rise and fall together, but they often disagree. In a large US study (MESA), when the two disagreed, heart events and artery thickness followed LDL-P more closely than LDL-C. Even so, a 2026 Circulation review says the current ACC/AHA guideline recommends against NMR and other advanced lipoprotein testing beyond a standard lipid panel, apoB and Lp(a), because it has not clearly improved risk prediction. Some clinicians still use LDL-P for people with high triglycerides, diabetes or insulin resistance.

If it’s low

A lower count means fewer LDL particles, which is the direction heart-health goals aim for. It is often the result of diet, lifestyle or cholesterol-lowering treatment. A very low count without treatment is uncommon. Sometimes it comes from an inherited condition or another illness, so a clinician may want to look into it.

Common causes

  • Cholesterol-lowering treatment
  • A diet low in saturated fat, regular activity and a healthy weight
  • An overactive thyroid
  • Poor absorption of nutrients (malabsorption) or malnutrition
  • Advanced liver disease
  • Rare inherited conditions that cause very low LDL

What can help

  • If you aren't on cholesterol treatment and your count is very low, ask your clinician whether anything else should be checked, such as your liver, thyroid or nutrient absorption

If it’s high

A higher count means more LDL particles are circulating. It usually causes no symptoms. Over many years, higher counts are linked to more plaque in the arteries and a higher chance of heart attack and stroke. Labcorp and Mayo sort results into low, moderate, borderline high, high and very high groups. Your clinician can put your result in context with your LDL cholesterol, apoB and other risk factors.

Common causes

  • High LDL cholesterol, since the two usually rise together
  • Eating a lot of saturated fat, found in fatty meat, butter, cheese and many baked goods
  • High triglycerides, low HDL cholesterol or insulin resistance, which are linked to more LDL particles that each carry less cholesterol
  • Extra body weight, little physical activity, prediabetes, type 2 diabetes or metabolic syndrome
  • Family history and genes, including inherited conditions such as familial hypercholesterolemia
  • An underactive thyroid, kidney problems such as nephrotic syndrome, or liver conditions that slow bile flow
  • Some medicines

What can help

  • Eat more vegetables, fruit, whole grains and nuts, and less saturated fat
  • Be active most days. Physical activity can lower LDL cholesterol and triglycerides
  • If you carry extra weight, ask your clinician about a realistic weight goal
  • Ask your clinician whether your result changes your plan, and whether apoB or non-HDL cholesterol would be a useful way to follow it
  • Ask whether thyroid, kidney, liver or blood sugar tests are worth checking as possible causes

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: up to 1,000 nmol/L. Source: Labcorp, Mayo Clinic Laboratories (testcatalog.org).

Labcorp and Mayo NMR LDL-P categories (exactly 2,000 nmol/L is 'High' at Labcorp and 'Very high' at Mayo)

  • Low (Mayo: Desirable)below 1,000 nmol/L
  • Moderate (Mayo: Above desirable)1,000 to under 1,300 nmol/L
  • Borderline high1,300 to under 1,600 nmol/L
  • High1,600 to under 2,000 nmol/L
  • Very high2,000 and above nmol/L

What can affect your result

  • Method: NMR (Labcorp, Mayo) and ion mobility (Quest) count LDL differently, and NMR counts include IDL, so results and ranges differ between labs
  • Fasting: Labcorp asks for 8 hours and Mayo requires 12 hours, while Quest's ion mobility test accepts a non-fasting sample
  • Triglycerides, insulin resistance, diabetes and body weight, which change how much cholesterol each LDL particle carries
  • Diet, especially saturated fat, and physical activity
  • Family history and genes
  • Thyroid, kidney and liver conditions
  • Cholesterol-lowering treatment
  • Labcorp asks for an 8-hour fast, and Mayo Clinic Laboratories requires a 12-hour fast with no alcohol for 24 hours before the draw. Quest's ion mobility test says fasting is preferred but a non-fasting sample is acceptable. Follow the instructions your lab gives you.
  • NMR and ion mobility count LDL differently. The NMR count includes IDL particles and is worked out from NMR signals, while ion mobility counts each LDL subclass directly, so results and ranges are not interchangeable between labs.
  • Labs reject samples that are grossly hemolyzed, contaminated with red cells, or held too long at room temperature (Labcorp), and grossly hemolyzed or lipemic samples (Quest ion mobility).
  • When triglycerides are above 800 mg/dL, Labcorp does not calculate LDL cholesterol, so LDL-C and LDL-P can't be compared on that report.

About 4 to 12 weeks to show the effect of a change in diet, weight or lipid-lowering treatment.

When to talk to a clinician

Talk with a clinician if your result is in your lab's 'High' or 'Very high' group (1,600 nmol/L or more on Labcorp and Mayo reports), or sooner if you have diabetes, a family history of early heart disease, or a very high LDL cholesterol. This test can't tell you whether you have heart disease. If you have chest pain or pressure, trouble breathing, or signs of a stroke such as face drooping, arm weakness or trouble speaking, call 911 or your local emergency number, whatever your results are.

Questions you could ask

  • Does it matter that my LDL cholesterol and my particle count don't match?
  • Should I use the same lab and method each time so my results can be compared?
  • Is my particle count high because of my LDL cholesterol, my triglycerides, or both?
  • Would apoB or non-HDL cholesterol be a useful way for us to follow this?
  • Should we check things that can raise LDL, such as my thyroid or blood sugar?
  • When should we recheck, and what would you like to see change by then?

Questions people ask

What is the difference between LDL-C and LDL-P?

LDL-C is the amount of cholesterol carried inside your LDL particles, in mg/dL. LDL-P is the number of LDL particles, in nmol/L. Particles can carry more or less cholesterol each, so the two numbers do not always match.

My LDL cholesterol looks fine but my LDL-P is high. What does that mean?

This is called discordance. In MESA, about 1 in 3 people with an LDL-C below 100 mg/dL had a noticeably higher LDL-P than their LDL-C suggested. It is more common in people with high triglycerides, low HDL cholesterol, insulin resistance or diabetes. When the two disagree, LDL-P followed heart risk more closely in that study. It is not a diagnosis, and your clinician can tell you whether it changes your plan.

Is LDL-P the same as apoB?

No, but they are related. Both count particles. ApoB counts every particle that carries apoB, including LDL, IDL, VLDL and Lp(a), while LDL-P counts LDL only (plus IDL on NMR). ApoB is a standard blood test that many labs run, and current US guidance mentions apoB but advises against routine NMR testing.

Why is my result different at Labcorp and Quest?

Labs use different methods. NMR (Labcorp, Mayo) and ion mobility (Quest) count LDL in different ways, and each lab sets its own ranges. Compare your result only with results from the same lab and method, and use the range printed on your own report.

Do I need to fast for this test?

Often yes. Labcorp asks for an 8-hour fast and Mayo Clinic Laboratories asks for 12 hours with no alcohol for 24 hours. Quest says fasting is preferred for its ion mobility test but not required. Follow the instructions your lab gives you.

Show the science and sources

For clinicians and researchers

LDL-P is the molar concentration of LDL particles in nmol/L. Labcorp and Mayo Clinic Laboratories measure it by proton NMR: signals from lipid methyl groups are deconvoluted into lipoprotein subclasses, and the NMR LDL-P total includes IDL. Quest's Cardio IQ method is ion mobility, a gas-phase electrophoresis that sizes and counts each particle directly, and Quest also offers an NMR version. Labcorp's categories (below 1,000; 1,000-1,299; 1,300-1,599; 1,600-2,000; above 2,000 nmol/L) sit at the 20th, 50th, 80th and 95th percentiles of 5,362 MESA participants not on lipid medication, and Mayo prints the same groups. In MESA, LDL-C and LDL-P correlated at r = 0.75. Where they differed by 12 or more percentile units (about half of participants), incident CVD was associated with LDL-P (HR 1.45 per SD, 95% CI 1.19-1.78) but not with LDL-C (HR 1.07, 0.88-1.30), and about 32% of people with LDL-C below 100 mg/dL had a discordantly higher LDL-P (LDL-P below 1,060 nmol/L and LDL-C below 100 mg/dL each fell below the 30th percentile). Discordance with LDL-P above LDL-C clusters with high triglycerides, low HDL-C, diabetes and metabolic syndrome. ApoB counts every apoB-containing particle (LDL, IDL, VLDL, Lp(a) and chylomicrons), while LDL-P is limited to LDL (plus IDL by NMR). Small LDL size and small LDL-P track risk but not independently of LDL-P. A 2026 Circulation review states that prospective studies have not shown meaningful risk reclassification from NMR measures, and that the current ACC/AHA guideline recommends against advanced lipoprotein testing beyond the lipid panel, apoB and Lp(a). Labcorp positions NMR LDL-P as a management tool in high-risk patients (type 2 diabetes, metabolic syndrome, CVD risk equivalent, statin-treated) to judge treatment response. Labcorp's and Mayo's test pages state that their versions were developed and validated by the laboratory and have not been cleared or approved by the FDA.

LOINC 54434-6 (primary). Specimen: serum-or-plasma.

Sources

  1. NMR LipoProfile+Lipids+Graph, sample patient report (test 123810), Labcorp (2024)
  2. NMR LipoProfile With Lipids (With Graph) (test 123810), Labcorp
  3. Nuclear Magnetic Resonance Lipoprotein Profile, Serum (test NMRLP), Mayo Clinic Laboratories (testcatalog.org)
  4. Cardio IQ Lipoprotein Fractionation Ion Mobility: clinical education FAQ, Quest Diagnostics
  5. Lipoprotein Fractionation, NMR (test 37847), Quest Diagnostics
  6. Cardio IQ Lipoprotein Fractionation, Ion Mobility (test 91604), Quest Diagnostics
  7. Clinical implications of discordance between low-density lipoprotein cholesterol and particle number, Journal of Clinical Lipidology (2011)
  8. Lipid Profile Testing and Interpretation (summarizes the 2026 ACC/AHA Dyslipidemia Guideline), Circulation (Nguyen, Ahmad, Navar) (2026)
  9. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol: Executive Summary, Circulation (2018)
  10. Blood Cholesterol: Treatment (lifestyle changes), National Heart, Lung, and Blood Institute

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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