Does correction of the friedewald formula using lipoprotein(a) change our estimation of ischemic heart disease risk? The Quebec Cardiovascular Study

Background: LDL-cholesterol is usually calculated using the Friedewald formula. This calculation method does not take into account the presence of Lp(a), which is associated with LDL-cholesterol. Dahlen has suggested that the Friedewald formula should be modified to account for Lp(a) associated cholesterol. This study was undertaken to determine if correction of the Friedewald formula would result in a better evaluation of ischemic heart disease (IHD) risk. Methods: 2222 men free from IHD were prospectively followed for 5 years for the appearance of myocardial infarction, coronary insufficiency or coronary death. At the baseline evaluation all had a complete fasting lipid profile which included Lp(a) determinations. LDL-cholesterol levels were calculated from total cholesterol, total triglycerides and HDL-cholesterol using the Friedewald formula and also using the Dahlen modification of the Friedewald formula. Results: During the follow-up there were 89 first IHD events. Both types of LDL-cholesterol calculations showed that the last tertile of the LDL-cholesterol distribution in comparison to the first tertile, doubles the relative risk (RR: 2.15; 95% confidence limits: 1.23–3.75) using the Friedewald formula (RR: 2.18; 95% confidence limits: 1.25–3.81) using the Dahlen modification. Lp(a) levels were not an independent predictor of IHD risk. Conclusion: Modification of the Friedewald formula to account for Lp(a) levels does not improve our evaluation of IHD risk.