Friedewald

Friedewald is a surname of German origin. It is best known in the medical field for the Friedewald equation, a formula used to estimate low-density lipoprotein cholesterol (LDL-C) from routine lipid measurements.

The Friedewald equation estimates LDL-C from total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG) in fasting plasma. The standard form is LDL-C = TC − HDL-C − TG/5, with TG expressed in milligrams per deciliter. In SI units (millimoles per liter), the equivalent form is LDL-C = TC − HDL-C − TG/2.2, assuming triglycerides are below 400 mg/dL (or 4.5 mmol/L). The method relies on a constant relationship between very-low-density lipoprotein cholesterol (VLDL-C) and TG and is most accurate when the patient has fasted and TG concentrations are not elevated.

Limitations include reduced reliability when TG is high (typically TG ≥ 400 mg/dL), when nonfasting samples are used, or in certain lipid disorders where lipoprotein composition deviates from the assumptions of the model. Despite these caveats, the Friedewald equation has been widely adopted in clinical practice because it provides a simple, cost-effective means to estimate LDL-C without direct ultracentrifugation or direct measurement.

The equation was first described in 1972 by Friedewald, Levy, and Fredrickson, and it has since become a standard reference in lipid profiling, though modern assays increasingly supplement or replace it with direct LDL-C measurements in some settings.