Did you know that there are better blood tests than total cholesterol and LDL cholesterol to predict future risk of heart problems such as coronary heart disease?  After all, the Centers for Disease Control says that half of all heart attacks occur in people with normal cholesterol levels.

I'll tell you about the better heart risk predictors, but first a little background to get you up to speed.

Warning: This is not water-cooler-conversation material.  Believe me, I wish there were a way to simplify it!  Since this is The Heart Health Blog, I had to get around to it eventually.

Cholesterol and trigyclerides (which are lipids) do not dissolve in our blood, which is mostly water.  Just like oil and water don't mix.  The cholesterol and triglycerides in our bloodstream have to be attached to proteins so that they can circulate.  Joining cholesterol or trigylceride to a protein creates a lipoprotein.

The five major lipoprotein classes include high density lipoprotein (HDL) and low density lipoprotein (LDL).  The lipoproteins can be further classified or fractionated based on the size and concentration (particle number) of the lipoproteins circulating in our blood. 

The protein component of the lipid-protein complex is called an apolipoprotein or apoprotein.  About ten specific apolipoproteins have been well-studied in humans.  The main protein associated with LDL cholesterol is apolipoprotein B-100.  All the lipoproteins that are linked with atherosclerosis are known as ApoB, which can be measured. 

When HDL cholesterol is measured, you're getting the amount of cholesterol physically linked to high density lipoprotein.  LDL cholesterol is the cholesterol in low density lipoprotein.

Traditionally, physicians have measured blood lipids to determine total cholesterol, HDL cholesterol (the good stuff), LDL cholesterol (boo!), and triglycerides.  In reality, the LDL cholesterol is usually a calculated value, although it can be measured directly.  The LDL calculation is worthless if triglycerides are over 400 mg/dl.

Rather than total cholesterol, it's elevated LDL cholesterol that is associated with heart disease.  That's why most physicians focus on LDL cholesterol.  A normal LDL level is under 130 mg/dl.  

LDL particles come in various sizes, from small and dense, to large and fluffy.  Large fluffy LDL particles may not be very harmful, if at all.  Small LDL particles seem to be the most damaging to our arteries.  The small LDL particles circulating in our blood are more likely to enter artery walls, become oxidized, then set off a cascade of events we eventually recognize as clinical atherosclerosis.  For too many people, the first clinical event is sudden death from a heart attack. 

The latest theory to explain most heart attacks is that it's the size and number of LDL particles that matters.

The size and number of LDL particles in our blood is a better predictor of heart disease than is the LDL cholesterol level.  ApoB, mentioned above, is also a better predictor.

In my next post, I'll review some practical applications of this new knowledge and theory.   

-Steve Parker, M.D.

References:

Ip, S., et al.  Systematic review: association of low-density lipoprotein subfractions with cardiovascular outcomes.  Annals of Internal Medicine, 150 (2009): 474-484.

Brunzell, John, et al.  Lipoprotein management in patients with cardiometabolic risk: consensus statement from the American Diabetes Association and American College of Cardiology Foundation.  Diabetes Care, 31 (2008): 811-822.