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May 2, 1990

Système International Units and Familiar Formulas: The Case of Lipids

JAMA. 1990;263(17):2302. doi:10.1001/jama.1990.03440170024029

To the Editor.—  In the article by Stern et al,1 we had difficulty understanding the formula used for calculating low-density lipoprotein cholesterol levels, ie, low-density lipoprotein cholesterol= total cholesterol — high-density lipoprotein cholesterol — serum triglycerides/5. Every time they mention triglyceride levels, units are expressed in millimoles per liter, and every time they mention cholesterol or high-density lipoprotein cholesterol levels, units are expressed in milligrams per deciliter. The formula is erroneous when the units are mixed together, and if Système International units are employed, the triglycerides' coefficient in the equation should be 2.18 instead of 5. It is not the first time that such a mistake has been made in a lipid article in an international publication.2,3 Indeed, the use of the Système International, contrary to the belief of its promoters, favors the mistake, because the expression of plasma lipid concentration still remains in milligrams per deciliter or