Friedewald LDL Equation: Estimates LDL cholesterol from standard lipid panel measurements (Total Cholesterol, HDL, and Triglycerides).
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
To estimate Low-Density Lipoprotein (LDL) cholesterol when a direct LDL measurement is not available (which is the standard in most clinical laboratories).
Do Not Use If
Triglycerides are severely elevated (>400 mg/dL or >4.5 mmol/L). The formula assumes a fixed ratio of triglycerides to VLDL cholesterol, which breaks down entirely in severe hypertriglyceridemia.
Section 2
Formula & Logic
The Formula
LDL = Total Cholesterol - HDL - Very Low Density Lipoprotein (VLDL). Since VLDL is difficult to measure directly, it is estimated as Triglycerides / 5 (if using mg/dL) or Triglycerides / 2.2 (if using mmol/L).
Underestimation Risk
01
The absolute ratio of TG to VLDL-C is rarely exactly 5. It varies across the spectrum of triglyceride and cholesterol levels.
02
When triglycerides are high (e.g., 200-399 mg/dL) or LDL is very low (<70 mg/dL), the Friedewald equation systematically underestimates true LDL levels.
03
This underestimation can falsely reassure clinicians and lead to undertreatment of high-risk patients.
Section 3
Pearls/Pitfalls
The Martin/Hopkins Alternative
The newer Martin/Hopkins equation replaces the fixed dividing factor of "5" with an adjustable factor derived from a 180-cell lookup table (ranging from 3.1 to 11.9) based on the patient's non-HDL cholesterol and triglyceride levels. It is significantly more accurate, especially when LDL is <70 mg/dL.
Non-HDL Cholesterol
In patients with hypertriglyceridemia, diabetes, or metabolic syndrome, calculating Non-HDL Cholesterol (Total Cholesterol - HDL) is often a better predictor of cardiovascular risk than estimated LDL, as it accounts for all atherogenic apolipoprotein B-containing lipoproteins.
Section 4
Evidence Appraisal
Original Derivation
Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge.
Friedewald WT et al. • Clin Chem.. 1972;18(6):499-502. The seminal paper outlining the calculation.
