Friedewald Formula (LDL Cholesterol)
Estimates LDL cholesterol from total cholesterol, HDL and triglycerides without ultracentrifugation.
When to use
Fasting adults with measured total cholesterol, HDL and triglycerides, when LDL was not measured directly and triglycerides are below 400 mg/dL.
Pearls and pitfalls
- The equation assumes that VLDL cholesterol is 20% of triglycerides (TG/5), a ratio that varies between people and with the triglyceride level.
- With triglycerides of 400 mg/dL or more the estimate is not valid; the interface flags the result instead of applying it silently.
- Chylomicrons and dysbetalipoproteinemia (type III) break the TG/5 assumption even with triglycerides below 400 mg/dL.
- The sample must be fasting; in the original paper the estimate was compared with ultracentrifugation, with correlations from 0.94 to 0.99 depending on the population.
- Negative values are possible when total cholesterol is very low and triglycerides are high; a negative LDL means the equation does not apply to that case.
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Formula
LDL cholesterol (mg/dL) = total cholesterol − HDL cholesterol − triglycerides/5.
Evidence
Empirical equation derived from 448 patients and compared with ultracentrifugation, with correlations from 0.94 to 0.99. The TG/5 term estimates VLDL cholesterol and becomes unreliable above 400 mg/dL of triglycerides.
References
- 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(6):499-502. doi:10.1093/clinchem/18.6.499
- Oliveira MJ, van Deventer HE, Bachmann LM, et al. Evaluation of four different equations for calculating LDL-C with eight different direct HDL-C assays. Clin Chim Acta. 2013;423:135-140. doi:10.1016/j.cca.2013.04.009
Frequently asked questions
What is Friedewald Formula (LDL Cholesterol)?
Estimates LDL cholesterol from total cholesterol, HDL and triglycerides without ultracentrifugation. Fasting adults with measured total cholesterol, HDL and triglycerides, when LDL was not measured directly and triglycerides are below 400 mg/dL.
How is the result calculated?
LDL cholesterol (mg/dL) = total cholesterol − HDL cholesterol − triglycerides/5.
How should the result be interpreted?
Empirical equation derived from 448 patients and compared with ultracentrifugation, with correlations from 0.94 to 0.99. The TG/5 term estimates VLDL cholesterol and becomes unreliable above 400 mg/dL of triglycerides.
What are the sources?
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(6):499-502. Oliveira MJ, van Deventer HE, Bachmann LM, et al. Evaluation of four different equations for calculating LDL-C with eight different direct HDL-C assays. Clin Chim Acta. 2013;423:135-140.