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The Friedewald Equation
- the ultracentrifugal measurement of LDL is time consuming and expensive
and requires specialist equipment. For this reason, LDL-cholesterol is most
commonly estimated from quantitative measurements of total and HDL-cholesterol
and plasma triglycerides (TG) using the empirical relationship of Friedewald
- [LDL-chol] = [Total chol] - [HDL-chol] - ([TG]/2.2) where all concentrations
are given in mmol/L (note that if calculated using all concentrations
in mg/dL then the equation is [LDL-chol] = [Total chol] - [HDL-chol] -
- the quotient ([TG]/5) is used as an estimate of VLDL-cholesterol concentration.
It assumes, first, that virtually all of the plasma TG is carried on VLDL,
and second, that the TG:cholesterol ratio of VLDL is constant at about
5:1 (Friedewald et al. 1972). Neither assumption is strictly true.
- Limitations of the Friedewald equation
- The Friedewald equation should not be used under the following circumstances:
- when chylomicrons are present
- when plasma triglyceride concentration exceeds 400 mg/dL (4.52 mmol/L)
- in patients with dysbetalipoproteinemia (type III hyperlipoproteinemia
Last reviewed 02/2021