Wednesday, June 8, 2011

Fasting blood tests

Every time I've had my cholesterol levels tested, I've been instructed to fast the night before heading to the lab for the blood test.  It's probably the same for you.

For some time now, I've been meaning to post an extensive study published in the Journal of the American Medical Association in 2009 that found that fasting makes no difference when it comes to your cholesterol.

The authors also concluded that measuring HDL relative to total cholesterol is no less effective than fractionating LDL.

You will recall that while blood tests can easily identify HDL and total cholesterol, the LDL count is derived by subtracting HDL and triglycerides from total cholesterol using the Friedewald formula.

Since LDL, or low density lipoprotein, comes in differing densities, not all of which are problematic, a more sophisticated, and hence more expensive, blood test is needed than the one we commonly get at our Canadian labs to identify the LDL components more accurately.  This is what is known as fractionating LDL.

You'll think I'm HDL-obsessed, but this study gives us one more reason to focus on the ratio of HDL to total cholesterol for heart health.  LDL, as far as I can tell, is relatively meaningless as far as its predictive powers for cardiovascular problems are concerned. 

Yet manufacturers of products that lower total cholesterol, conveniently don't go into any further detail when their cholesterol-lowering product does nothing to raise HDL.

I won't have an appointment scheduled for a little while yet, but I'm interested to show my family physician this study when I do go.  Where we live, fractionated LDL isn't an option, but I'm curious whether she will prescribe a fasting cholesterol test.   However, I suspect I know the answer to that already.

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