Lp(a) in mg/dL and nmol/L: why there is no conversion factor

Lipoprotein(a), or Lp(a), is reported in two units that measure different things. mg/dL is the weight of the particles. nmol/L is the number of them. For most lab tests, going from one to the other takes a single factor. For Lp(a) it doesn’t, because the particles come in different sizes, and the size is set by your genes. The 2022 European Atherosclerosis Society consensus statement says plainly: “This panel does not recommend using a standard factor to convert between mg/dL and nmol/L, as assays vary extensively.”

You don’t need a conversion to read your result, though. Each unit has its own cutoffs. Enter your result in the unit your report uses.

Why one factor doesn’t work

An Lp(a) particle is an LDL particle with an extra protein, apolipoprotein(a), wrapped around it. That protein contains a repeating section, and the number of repeats varies from person to person, from a few copies to more than 40. Each repeat adds weight. Two people with the same number of Lp(a) particles can have very different mg/dL results because one person’s particles are much heavier.

So the number of nmol/L in each mg/dL depends on the person, not just the test. The EAS panel calls a factor of 2 to 2.5 “only a ‘best guess’” for comparing the two units in general. For one person, the true figure can fall outside that range, and it tends to be lower in people with large, heavy particles. That’s why the calculator shows a span for the other unit and labels it a guess.

The cutoffs in each unit

The EAS statement gives cutoffs in both units. They are not conversions of each other. Each was set for its own kind of measurement.

The 2026 ACC/AHA dyslipidemia guideline uses the same 125 nmol/L line: at or above it, Lp(a) counts as a risk enhancer when deciding on treatment. Some European labs report in mg/L, which is a mass unit and does convert: 300 mg/L is 30 mg/dL. The calculator handles that for you.

Measure once, then compare like with like

Lp(a) is mostly set by your genes, so it changes little over a lifetime. The EAS panel and the 2026 ACC/AHA guideline both recommend measuring it at least once in every adult. Many people will only ever have one or two results.

If your history has Lp(a) in both units, from two labs or two eras, don’t convert one to match the other. Keep each result in its own unit and read it against that unit’s cutoffs. A result of 60 mg/dL and a later 140 nmol/L are both above the “rule in” line, and that is the comparison that holds up. Saying the second is “higher” isn’t meaningful.

Labs that report nmol/L should use an assay that isn’t affected by particle size and is calibrated to the international reference material. Older mg/dL assays often weren’t, which is one more reason the two kinds of result don’t line up.

Lp(a) and the rest of your lipid panel

Lp(a) carries cholesterol, so it’s counted inside your total cholesterol, non-HDL, and often your LDL as well. A high Lp(a) can make LDL look less responsive to treatment than it is. The non-HDL and remnant cholesterol calculator and the LDL cholesterol calculator cover the rest of the panel, and how to track your cholesterol over time covers charting it. For every other test, the lab unit converter has a real conversion factor.

Lp(a) in HealthViewer

HealthViewer is a lab results tracker that runs on your own computer. It imports Lp(a) from lab report PDFs, MyChart downloads, and direct connections to your health system. It treats mg/dL and nmol/L as units that can’t be converted, so a result in one is never plotted on the other’s scale. In Trends, a result it can’t put on the chart is left off with a note saying why.

Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.

This page is for understanding your lab report, not for making treatment decisions. Ask your clinician what your Lp(a) result means for you.