Effect of hormone replacement therapy on the validity of the Friedewald equation in postmenopausal women: The Postmenopausal Estrogen/Progestins Interventions (PEPI) trial

The Friedewald equation is often used to estimate low-density lipoprotein c holesterol (LDL-C). Hormone therapy is known to raise triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) and alter lipid contents of l ipoproteins. We compared Friedewald estimated LDL-C to measured LDL-C in PE PI participants on placebo or four different hormone treatment groups. At b aseline, the 0.2 coefficient for triglyceride (TG) was accurate for all fiv e treatment groups. Among women who took >80% of their pills and whose TG w as <4.5 mmol/l (400 mg/dl), LDL-C was underestimated for 69-82% of the part icipants in the active treatment groups, compared to 50% in the placebo gro up. After 3 years of therapy, the TG coefficient that offered a better fit of the Friedewald equation in the active treatment groups was 0.39 for the equation in mmol/l (0.17 for the equation in mg/dl). Using this coefficient is clearly warranted for greater accuracy in research studies. (C) 1999 El sevier Science Inc.