There’s more to LDL cholesterol: Particle size and number

There’s more to LDL cholesterol: Particle size and number

By Dr. Elizabeth Klodas  

Did you know that the regular cholesterol profile might not provide you with all the information you might need about your LDL? Turns out, the LDL story goes deeper.

Conceptually, when you get your LDL number, what we’re giving you is a value measured in mg/dL – or milligrams per deciliter. Huh?? A milligram is a unit of weight and a deciliter is a unit of volume. So what we’re telling you is that in a certain volume of blood, you have a certain weight of LDL cholesterol. This actually tells us nothing about the NUMBER OF LDL PARTICLES circulating in your blood stream.  And this is a significant piece of missing information, since LDL can exist in many forms – ranging from very small to very large particles. 

Which means that the total LDL weight might be coming from a few large particles or many small particles - small particles being worse since they can more easily sneak into artery walls, and because there would be more of them.  So you not only want a low LDL cholesterol mg/dL value, you also want the "mg" part to be made up of large particles.  And unless you know particle size or number, you can’t be sure if that’s the case.  Testing for LDL particle size and number is called “LDL subfraction analysis”. 

But if knowing particle size could tell us more, why isn't subfraction analysis a routine test?

Accurately determining particle size and number is much more difficult to do and requires specialized lab equipment, which is not universally available.  And the test is much more expensive to perform compared to a regular cholesterol check. Plus, it’s not always critical to know this information. 

For example, we have some major clues as to your LDL particle size based upon what we know about you and about your other findings in the cholesterol profile – diabetics, overweight individuals, and patients with high triglyceride levels and low HDL tend to have small LDL particles – making it less critical to check this test in some patients.

Furthermore, most of the major studies that have looked at the effects of cholesterol on heart disease have only dealt with the mg/dL type of LDL measurements, and all the recommendations for LDL goals have used the mg/dL values, removing LDL particle number/size from routine clinical use. 

So if your doctor has never checked your LDL particle number (or size), you are not alone.  And to be honest, even I don’t check these values very frequently.

What I find more useful is checking something called Apoprotein B.  Apoprotein B is a protein that attaches itself to all the really toxic cholesterol particles – especially small LDL.  So an Apoprotein B level is like a marker of how much of your cholesterol is in the most unfavorable form.  And it’s a widely available and inexpensive test.

And what I look for is a discrepancy between ApoB and LDL findings. So if LDL is high and ApoB is low, I’m feeling a bit better about the LDL level (since the low ApoB level is telling me that the LDL weight is made up of larger, less toxic particles).  If LDL is low and ApoB is high, I know that we may need to be more aggressive in terms of cholesterol lowering (since I’m dealing with a bunch of small particles).

You should know that I don’t test ApoB all the time either.  I find this test to be most helpful in instances where what to do (start a drug or don’t start a drug) is not absolutely clear. Normal ApoB levels fall below 100 mg/dL.  In individuals with known heart or vascular disease or with diabetes, ApoB should fall below 80 mg/dL.  And in case you're wondering, ApoB has nothing to do with Lipoprotein A, which is yet another marker of risk that doesn't show up in a regular cholesterol profile.

OK. That was a lot of information about the minutiae of cholesterol assessment. And it’s easy to get lost in this stuff and go down rabbit holes, especially if you start googling. Which is why I need to bring us back to the bigger picture. In the end, the “cure” for small particles is the same as the cure for nearly everything that ails us – a healthful diet, regular exercise and attainment/maintenance of a healthy weight. 

So just know that when you’re eating a Step One bar, going for a walk or doing something else good for heart health, your efforts are likely translating not only into lower LDL cholesterol mg/dL values but also improved LDL particle size.


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