Friedewald Equation (LDL)

The Friedewald equation is a mathematical formula used to estimate low-density lipoprotein cholesterol (LDL-C), which is the primary indicator of atherogenic risk and cardiovascular disease. LDL-C represents the amount of cholesterol carried by low-density lipoprotein particles in the blood, typically expressed in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). The estimated LDL-C calculated by the Friedewald equation has been the standard method for assessing lipid profiles in daily clinical practice for decades, superseding the need for costly and time-consuming preparative ultracentrifugation. The formula was developed in 1972 to provide a highly accessible and practical estimation of LDL-C based on a standard fasting lipid panel. The calculation uses three main variables: total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides. However, the use of a fixed constant to estimate very-low-density lipoprotein (VLDL) by dividing triglycerides by 5 loses accuracy at extremes and is strictly invalidated when triglyceride levels exceed 400 mg/dL, prompting the adoption of newer, adjustable formulas (like the Martin-Hopkins or Sampson equations) for patients with high triglycerides or very low LDL-C. The LDL-C estimated by this equation is fundamental for cardiovascular risk stratification, diagnosing dyslipidemia, and guiding lipid-lowering therapies, such as initiating or adjusting the dosage of statins to meet specific clinical targets.