LDL cholesterol - Change from Friedewald equation to Sampson equation
15 Feb 2026
We are changing the way we calculate LDL-C from Friedewald equation to Sampson equation with effect from Monday 23 February.
Full story
Effective immediately, LDL-cholesterol will now be reported in patients with serum triglycerides up to 9 mmol/L, as the method of estimation of LDL-C is changing from Friedewald to the Sampson equation.
What is the reason for this change?
Friedewald’s formula has been in use for 40-50 years for estimation of LDL-C from measured total cholesterol, HDL-cholesterol (HDL-C) and triglyceride (TG) levels.
The calculation assumes that triglyceride containing lipoproteins contain a constant proportion of LDL-C and uses a fixed number constant.
But this has been shown not to be the case and as the plasma concentration of TG rises, so does the proportion of cholesterol in the triglyceride-rich VLDL particles.
LDL-C calculation using the Friedewald formula becomes increasingly inaccurate above 2.5 mmol/L TG and is sufficiently unreliable to be not reported when TG >4.5 mmol/L.
In 2020, Sampson et al published a new equation that links total cholesterol (TC), HDL-C, TG and non-HDL-C in the calculation of LDL-C.
It was compared to the Friedewald equation and to direct methods of LDL-C estimation (including ‘gold-standard’ Beta quant - ultracentrifugation with cholesterol estimation).
Health Service Laboratories (HSL) have conducted our own studies comparing the Sampson equation to a direct method of measuring LDL-C and the gold standard Beta quant measurement.
The study showed better agreement between the Sampson method and direct LDL-C methods than the Friedewald formula up to a TG concentration of 9 mmol/L.
The Sampson equation provides a more accurate calculation of LDL-C than the older Friedewald equation, especially when triglyceride (TG) levels are high (up to 9.0 mmol/L) or LDL-C is very low.
Using the Sampson equation will result in fewer LDL-C values being unavailable because of high TG. The Sampson equation is more accurate at very low levels of LDL-C that are being reported now with use of more aggressive lipid control. There is likely to be little difference in LDL-C estimation in patients who currently receive a result as calculated by the existing Friedewald equation as there is excellent agreement between the two formulae at this level.
Contact:
Please contact the duty biochemist (duty.biochemist@hslpathology.com) if there are any issues associated with this change.
We sometimes use Artificial Intelligence to assist us in creating intranet content as efficiently as possible. In line with the Trust's acceptable use of AI policy, all AI generated content is checked by the communications team before it is published.