EFFECT OF SERUM LIPOPROTEIN(A) ON ESTIMATION OF LOW-DENSITY-LIPOPROTEIN CHOLESTEROL BY THE FRIEDEWALD FORMULA

The calculation of serum low-density lipoprotein cholesterol (LDL-C) b y the Friedewald formula does not account for the cholesterol associat ed with lipoprotein(a) Lp(a). To quantify the contribution of Lp(a) cholesterol to total serum cholesterol, we measured concentrations of serum Lp(a) by an ELISA and concentrations of other serum lipids and l ipoproteins by standard assays in 23 normolipemic women, ages 50-60 ye ars. In measuring serum high-density lipoprotein we found that polyeth ylene glycol 6000 precipitated >99.8% of all Lp(a). When serum Lp(a) c oncentrations were less than or equal to 300 mg/L, 301-600 mg/L, and > 600 mg/L, the uncorrected serum LDL-C was overestimated, respectively, by a mean of 4.1% (n = 7), 8.5% (n = 8), and 21.4% (n = 8). Serum Lp( a) concentrations were positively correlated with percentage overestim ation (P <0.001), but were not correlated with either corrected or unc orrected serum LDL-C. We conclude that the Friedewald formula should b e modified to take into account the contribution of Lp(a) cholesterol to total serum cholesterol.