The Friedewald’s equation [Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18:499-502. (Cited in: Clin. Chem. 1990; 36:15-19)] is used to calculate VLDL (very low density lipoprotein) and LDL (low density lipoprotein) cholesterol levels in a lipoprotein estimation test. In this method, total cholesterol, triglycerides and HDL cholesterol are directly estimated using reagents.
VLDL = Triglycerides/5
LDL = Total cholesterol – (HDL + VLDL)
This method of indirect LDL estimation becomes unreliable when the triglyceride levels are high. In that case direct LDL measurements have to be resorted to. Some laboratories are switching to direct LDL measurements in all situations.