The patients who have CHD or CHD risk equivalents should have LDL-C level less than 100 mg/dL because of the great reduction of risk for major coronary events. Direct measurement of LDL-C is the most accurate but is expensive. But with the practical use of the Friedewald equation for calculating LDL-C, the authors noticed that the accuracy declined with triglyceride level being higher than 300 mg/dL. The authors determined the correlation of direct measurement of LDL-C with calculation LDL-C from the Friedewald equation and postulated the new modified Friedewald equation for calculating LDL-C by using 1/6 triglyceride to minus. From a total of 1079 fasting serum samples analysis, and determining the correlation of LDLC from the direct measurement (dm LDL) while calculating LDL-C from equations of the standard Friedewald (sf LDL), and the new modified Friedewald (mf LDL), by using 1/6 triglyceride to minus instead of 1/5 triglyceride, if triglyceride was over 200 mg/dL. The authors found an excellent correlation within 0 + 10% difference of dm LDL and sf LDL if triglyceride was less than 200 mg/dL, but sf LDL is less accurate when the triglyceride level is high, and mf LDL has better correlation with dm LDL within 0 + 10% that sf LDL vs mf LDL, 72.3% vs 91.6% (p = 0.0001), and 58.3% vs 83.3%, (p = 0.01) when the triglyceride level is 200 -299, and 300–399 mg/dL respectively. It is shown that sf LDL has more underestimation than mf LDL when compared with dm LDL (more than 10 mg/dL) as 26.9% vs 2.5% (p < 0.0001) and 41.6% vs 5.6% (p = 0.0003) with triglyceride of 200-299, and 300–399 mg/dL respectively, although mf LDL showed overestimation of more than 10 mg/dL difference with dm LDL as sf LDL vs mf LDL of 0.8% vs 5.8% ( p = 0.03), and 0.0% vs
11.1% (p= 0.03) if the triglyceride is in the range of 200-299 and 300-399 mg/dL respectively, even with a triglyceride level of 400-499 mg/dL, mf LDL still has good correlation with dm LDL up to 75.0%. The authors conclude that the standard Friedewald equation is excellent for LDL calculation if triglyceride is less than 200 mg/dL, but the accuracy is declined when triglyceride is over 200 mg/dL, the authors offer a new modified Friedewald equation to calculate LDL-C if triglyceride is in the range of 200-499 mg/dL which has a better correlation with direct measured LDL-C. However this new modified Friedewald equation needs to be testified again especially with dyslipidemic patient sera.

Keyword : Calculating LDL-C, Friedewald equation, New modified Friedewald equation, Ban Paew Project