Advanced Lipid Testing (NMR LipoProfile, ApoB, Lp(a))#

LDL-C is the amount of cholesterol carried by all LDL particles combined, in mmol/L.

LDL-P is the number of LDL particles, regardless of how much cholesterol each is carrying.

Most of the time these track together, but in about 20 to 30% of people they do not. Someone with lots of small, cholesterol-poor LDL particles can have a normal LDL-C but a high LDL-P - and they carry the cardiovascular risk that goes with the particle number, not the cholesterol amount.

A high LDL-P or ApoB means you have a lot of cholesterol-carrying particles in your blood that can deposit in artery walls. Numerous studies have shown that LDL-P and ApoB are stronger predictors of future heart attack and stroke than LDL-C alone. If your LDL-P or ApoB is high - even with a normal LDL-C - the same lifestyle and medication strategies that lower LDL-C also lower particle number.

Discordance is when LDL-C and LDL-P (or ApoB) tell different stories. Two common patterns:

• Low LDL-C, high LDL-P / ApoB: many small cholesterol-poor particles. Common in diabetes, metabolic syndrome, and high triglycerides. Risk is higher than the LDL-C suggests.
• High LDL-C, lower LDL-P / ApoB: fewer but larger cholesterol-rich particles. Risk is lower than the LDL-C suggests.

When discordance is present, most cardiology guidelines now recommend treating to the LDL-P or ApoB target rather than the LDL-C target.

NMR can also report whether your LDL particles are predominantly:

• Pattern A - mostly large, buoyant particles. Lower risk.
• Pattern B - mostly small, dense particles. Higher risk. Common with diabetes, abdominal obesity, and high triglycerides.
• Pattern AB - intermediate.

Pattern B is improved by the same things that lower triglycerides: weight loss, less refined carbohydrate, regular exercise, and treatment of insulin resistance.

Lp(a) is a particle that looks like LDL but has an extra protein attached. Your Lp(a) level is roughly 90% determined by your genes and is essentially set from childhood. It does not change much with diet, exercise, or most cholesterol-lowering medications. So a single measurement in adulthood tells you your lifetime risk, and there is no need to repeat it.

High Lp(a) is independently linked to:

• Heart attack and stroke at younger ages
• Aortic valve narrowing (calcific aortic stenosis)
• Family clusters of early cardiovascular disease

Diet and exercise do not meaningfully lower Lp(a). The standard approach is:

• Aggressively control everything else that contributes to cardiovascular risk - LDL, blood pressure, diabetes, smoking, weight. The total risk is what matters, and you can lower the other contributors.
• Many clinicians use a lower LDL or ApoB target when Lp(a) is high.
• Newer medications that specifically lower Lp(a) are in clinical trials but not yet approved for general use in Canada.
• Family screening: if your Lp(a) is high, your first-degree relatives have about a 50% chance of also having high Lp(a) and should consider one-time testing.

Sometimes useful. Cholesterol-lowering medications (especially statin-class medications) lower both LDL-C and LDL-P, but they often lower LDL-C more than LDL-P percentage-wise. So a patient at LDL goal on medication may still have a high LDL-P or ApoB - "residual risk."

In this situation, an ApoB or NMR can guide whether your clinician should:

• Add a second cholesterol-lowering medication
• Adjust your current dose
• Reassess other risk factors

This is usually only done if there is a specific clinical question - it is not routine for every patient on a statin-class medication.

Yes - for ApoB, LDL-P, particle size, and triglyceride-rich remnants:

• Weight loss of 5 to 10% improves all of these
• Lower refined carbohydrate intake improves triglycerides, particle size, and HDL
• Regular aerobic exercise (150+ minutes per week) raises HDL particle number and lowers LDL-P modestly
• Quitting smoking improves multiple lipid measures and lowers cardiovascular risk substantially

Lp(a) is the exception - it does not respond meaningfully to lifestyle change.

NMR has been validated in several large cardiovascular studies, including data from the Framingham Heart Study and MESA (Multi-Ethnic Study of Atherosclerosis). LDL-P measured by NMR is a strong predictor of future cardiovascular events. The test is technically reliable, but Canadian guidelines have not yet adopted NMR-specific targets the way they have for ApoB - so clinicians interpret NMR results in the broader context of your standard lipid panel and overall risk.

Atherogenic risk is the risk of developing atherosclerosis - the buildup of cholesterol-rich plaque in artery walls that causes heart attacks and strokes. Particles that contain ApoB (LDL, VLDL, IDL, Lp(a)) are the ones that drive atherosclerosis, which is why ApoB and LDL-P are often called "atherogenic particle counts."

Several reasons:

• Canadian provincial health plans do not cover NMR, so cost is a barrier.
• Treatment thresholds and targets are still defined using LDL-C and ApoB in most guidelines.
• For most patients, ApoB plus a standard lipid panel plus a one-time Lp(a) captures the information that NMR adds, more cheaply.

NMR is most useful when there is a specific clinical question that LDL-C and ApoB cannot answer - which is a minority of patients.

ApoB, LDL-P, particle size, and triglyceride-rich remnants all respond to lifestyle changes and to cholesterol-lowering medications - sometimes within 8 to 12 weeks. Lp(a) does not change meaningfully and only needs to be measured once in your lifetime.

• ApoB: generally not insured as a stand-alone test in most provinces - usually self-pay through TeleTest's partner labs.
• Lp(a): generally self-pay.
• NMR LipoProfile: self-pay through Dynacare.

If you have private insurance, some plans reimburse advanced lipid testing with a prescription - check with your insurer.