"Routine use of . . . LDL subfraction tests to estimate cardiovascular disease risk is premature," according to a recent review in the Annals of Internal Medicine.

Huh?  What the . . . ?

I'm starting to see advertisements for "advanced lipoprotein testing" to help clarify one's risk for developing serious heart disease, or to assess response to therapy for abnormal cholesterol and other blood lipids.  Cholesterol testing originally involved total cholesterol and the theory that high total cholesterol caused heart attacks.  Then we learned that heart attacks were more accurately linked to a specifiic type of cholesterol: LDL cholesterol. 

The Centers for Disease Control reports that half of all heart attacks occur in people with "normal" cholesterol levels.  So we have a lot of 'splainin' to do.  [That's "explaining" to those of you outside the South.]

Advanced lipoprotein testing breaks down LDL cholesterol further into the type and number of LDL cholesterol particles in the blood, which I wrote about recently.  Type refers to the size of LDL particles, for example, small and dense or large and fluffy.  It appears now that type and number of LDL particles are the most accurate lipid predictors of future heart attacks.

Some speculate that the late broadcaster Tim Russert, who died of sudden cardiac death, may have had a preponderance of small dense LDL or high LDL particle number, while having normal LDL cholesterol.   

[Doesn't this make you wonder what theory we'll have to explain heart attacks twenty years in the future?]

Some physicians and researchers recommend that clinicians focus on LDL particle size, number, and other subfractions (e.g., B-100, lipoprotein(a), ApoB) rather than total and LDL cholesterol values.  Hence, the increasing availability of advanced lipoprotein testing to determine these numbers.  NMR spectroscopy is the  current leader among the three competing measurement technologies. 

I found one company that offers the NMR test for about $100 USD.  Not too bad as far as lab tests go, although some sources describe the test as expensive.

I can imagine some scenarios where the advanced testing might be helpful, such as hereditary early-onset heart attacks, management of difficult lipid situations, or to convince someone at increased heart risk he really better do something about his abnormal lipids. 

I would also consider doing the test in someone with a normal LDL cholesterol but with multiple or serious risk factors for heart disease: the normal LDL cholesterol could be falsely reassuring if the LDL particle number is high. 

Here are some problems with using advanced lipoprotein testing widely among the general public.  It's never been shown that such testing offers any additional benefit over traditional risk factor assesement and management.  And all of the established clinical management guidelines utilize LDL cholesterol rather than LDL subfractions. Physicians know what to do with LDL cholesterol.  We don't have evidence-based protocols that tell us what to do with these subfractions. 

Advanced lipoprotein testing has great potential.  But the Annals article mentioned above suggests that the test is not helpful at this point for screeening the general public for heart disease risk, despite advertising to the contrary. 

-Steve Parker, M.D.

References:

Ip, S., et al.  Suytematic Review: association of low-denisty 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.