You went for your annual and your cholesterol test checked out just fine, so you’re all set, right? Think again, say researchers from Johns Hopkins School of Medicine who recently found the standard formula used to calculate LDL (bad cholesterol) to be largely inaccurate.

The widely used formula, known as the Friedewald equation, is more an estimate than a measurement, said researchers, and it underestimates LDL (bad) cholesterol in high-risk patients. In this group, such inaccuracies can have serious negative repercussions as doctors often base risk assessments and treatment options on the equation. The equation involves taking total cholesterol minus HDL cholesterol minus triglycerides divided by five.

When researchers compared samples (detailed lipid profiles from more than 1.3 million adults) gathered using the Friedewald equation to direct calculations of LDL cholesterol, they found that nearly one in four samples from the high-heart-disease-risk patients, which was cleared as being in the desirable range, was actually wrong. Thus, many patients were led to believe they had reached their target LDL (bad) cholesterol levels, when, in fact, they had not. The common goal is to reduce LDL to below 70.

As an alternative, researchers suggest looking at non-HDL (subtracting HDL from total cholesterol) as a more accurate measure. This number (which includes LDL and other plaque-causing VLDL, or Very Low-Density Lipoproteins) would be about 30 points higher but would provide a better indication of heart health. Researchers add that this measure can be easily obtained using the same test at no extra cost.

“Non-HDL cholesterol is a much better target for quantifying risk of plaques in coronary arteries,” said Jones, in a statement. “Looking at non-HDL cholesterol would make it simpler and more consistent.”

If you are being monitored for high cholesterol, a risk factor for heart disease, ask your doctor whether analyzing your non-HDL is an appropriate and possible step in measuring your heart health and progress in reaching your target cholesterol goals.

How often do You have your cholesterol levels tested? 

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