Lp(a) results come in one of two units. Milligrams per deciliter (mg/dL) reports the weight of Lp(a) in your blood. Nanomoles per liter (nmol/L) reports the number of Lp(a) particles. A result of 60 means something very different depending on which unit follows it.
You cannot convert one unit into the other exactly, because Lp(a) particles differ in size from person to person. So the first step in reading your report is to find the unit. Then compare your number with the threshold for that unit: 50 mg/dL or 125 nmol/L.
Key takeaways
- Always read the unit before the number, since the same figure can be low in one unit and high in the other.
- The high-risk mark is 50 in mg/dL and 125 in nmol/L.
- Any conversion between the two is an estimate, so do not rely on a calculator for a borderline result.
- Results between the low and high marks sit in a gray zone and are read with the rest of your risk.
Two units that measure different things
The mg/dL unit is a mass measurement. It weighs the whole particle: its protein, cholesterol and other fats. The nmol/L unit is a count of how many particles are present in a given volume of blood.
For most blood tests, switching between weight and count is simple arithmetic, because every molecule weighs the same. Lp(a) is the exception.
Why you cannot convert exactly
Each Lp(a) particle carries a protein called apolipoprotein(a). Your genes decide how long that protein is, and its length differs widely between people. Some people make short, light versions. Others make long, heavy ones.
That means two people with the same number of particles can have different total weights. One conversion factor cannot be right for both of them. Lab methods add to the problem, since many tests react differently to small and large versions of the protein.
The European Atherosclerosis Society does not recommend using a standard factor to convert between mg/dL and nmol/L.1 It describes a factor of 2 to 2.5 as only a best guess.1 You will see "multiply by 2.5" online. Treat the answer as a rough guide and nothing more.
Thresholds in each unit
Because the units do not convert cleanly, expert groups publish their cut points in both.
| Risk reading | mg/dL | nmol/L |
|---|---|---|
| Low | Below 30 | Below 75 |
| Intermediate (gray zone) | 30 to 50 | 75 to 125 |
| High | 50 or more | 125 or more |
The National Lipid Association considers levels below 75 nmol/L (30 mg/dL) low risk, levels of 125 nmol/L (50 mg/dL) or more high risk, and levels in between intermediate risk.2
US cholesterol guidance uses the same high mark, 50 mg/dL or 125 nmol/L, as a risk-enhancing factor.34 Notice that these pairs are themselves built on the rough 2.5 factor. They are practical markers, not exact equivalents.
The cut points are also simplifications. Risk rises steadily as Lp(a) rises, with no sudden step at 50 or 125. An Lp(a) of 100 mg/dL, or roughly 250 nmol/L, approximately doubles the risk of cardiovascular disease.1 A result just over the line and a result several times over it are both "high", but they do not carry the same weight.
How to read your report
- Find the unit first. It is printed next to the result or in the reference range column.
- Use the threshold for that unit. Compare an mg/dL result with 30 and 50. Compare an nmol/L result with 75 and 125.
- Check the lab's own flag. Reference ranges differ between laboratories and test methods.
- Keep the lab name with the result. Experts advise that reports name the test method, so that results from different labs can be traced and compared with care.
- Be careful near a cut point. A result of 48 mg/dL and one of 52 mg/dL are effectively the same. Do not read much into which side of the line you fall.
If you have two results in different units, do not expect them to match after conversion. A gap between them usually reflects the units and the test method, not a change in you.
Which unit is better
Expert groups prefer nmol/L. The European consensus says Lp(a) should be measured in molar units where available, because a particle count is not distorted by particle size in the same way.1 Plenty of US labs still report mg/dL, and a result in either unit can be interpreted. What matters is using the right threshold.
Do you need a repeat test?
Usually not. Your level is set mostly by your genes, and with a few exceptions, such as kidney or liver disease and acute infections, repeat measurement is not required.1 Levels in women tend to rise around menopause, which is one situation where a clinician may choose to look again. Our Lp(a) test guide explains why one measurement is generally enough.
You do not need to fast for this test on its own. Lp(a) is not affected by whether you have eaten.5
If your result is high, the next read is what to do about a high Lp(a).
Lp(a) in a Cardio Res-Q assessment
Lp(a) is part of the lab panel in both Cardio Res-Q assessments, the Comprehensive Assessment ($775) and the Enhanced Assessment ($999). It is measured once, as an inherited baseline, and read alongside ApoB, hs-CRP and your metabolic labs. If you want to know which unit your report will use, ask our team.
The clinic asks you to fast for 10 to 12 hours because of the other tests in the panel. For the full sequence, see what to expect at your assessment, or go to the Cardio Res-Q program page to book.
Are You a Candidate for Cardio Res-Q?
Three quick questions about the risk factors we screen for. Your answers stay between you and the clinic.
Frequently asked questions
Can I just multiply mg/dL by 2.5 to get nmol/L?
Only as a rough estimate. The true relationship differs from person to person and from one lab method to another, so the answer may be noticeably off. For a result near a threshold, do not rely on it.
My Lp(a) is 40 mg/dL. Is that high?
It falls in the intermediate range of 30 to 50 mg/dL. It is not classed as high on its own, but it can matter more if you have other risk factors or a family history of early heart disease. Your clinician will read it with the rest of your results.
Why did two labs give me different Lp(a) numbers?
The most common reason is that they used different units. Even in the same unit, test methods vary in how they respond to different particle sizes. A real change in your level is the least likely explanation.
My report says 150 with no unit. What should I do?
Ask the lab or the clinician who ordered it. A result of 150 nmol/L is modestly above the high mark, while 150 mg/dL would be very high. The unit changes the meaning completely.
Related reading
This article is for general education and is not medical advice. Decisions about testing and medication should be made with your clinician. If you have chest pain or other symptoms of a heart attack, call 911.
