Ans. d. 245 (Ref :Harrison 19/e p2446; Clinical Laboratory Medicine by Kenne 2/e p3I9)"Plasma lipid and lipoprotein levels should be measured in all adults, preferably after a 12-h overnight fast. In most clinical laboratories, the total cholesterol and TGs in the plasma are measured enzymatically, and then the cholesterol in the supernatant is measured after precipitation of apoB-containing lipoproteins to determine the HDL-C. The LDL-C is then estimated using the following equation: LDL-C = total cholesterol -- (TG/5)-HDL-C (The VLDL cholesterol content is estimated by dividing the plasma TG by 5, reflecting the ratio of TG to cholesterol in VLDL particles.) This formula (the Friedewald formula) is reasonably accurate if test results are obtained on fasting plasma and if the TG level does not exceed ~200 mg/dL; by convention it cannot be used if the TG level is >400 mg/dL. "--Harrison 19/e p2446Friedewald EquationThe ultra centrifugal measurement of LDL is time consuming & expensive and require specialist equipment.For this reason, LDL-cholesterol is most commonly estimated from quantitative measurements of total and HDL-chntesterol and plasma triglycerides using the empirical relationship of Friedewald et al.Total cholesterol = LDL + HDL + Triglycerides/5Total cholesterol = LDL + HDL + Triglycerides/5300 = LDL+ 25+ 150/5LDL = 300 - (25 + 30) = 245 mg/dlLimitations of Friedewald EquationFriedewald Equation should not be used under the following circumstances:When chylomicrons are presentWhen plasma triglyceride concentration exceeds 400 mg/dLIn patients with dysbeta-lipoproteinemia (type III hyperlipoprteinemia)