What is the maximum triglyceride level for which the Friedewald formula for computation of LDL-cholesterol is valid?

The Friedewald formula is used to estimate low-density lipoprotein (LDL) cholesterol levels based on total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides. This formula is valid under certain conditions, particularly regarding triglyceride levels.

The formula becomes less accurate when triglyceride levels are elevated. Specifically, the Friedewald equation is typically reliable when triglyceride levels are less than 400 mg/dL. When triglycerides exceed this threshold, the estimation of LDL cholesterol can become significantly incorrect because the assumptions underlying the formula break down.

In essence, the formula assumes that the triglycerides in the very low-density lipoprotein (VLDL) fraction can be estimated by dividing triglyceride levels by a factor (usually 5 or 6, depending on the laboratory's approach). However, at higher triglyceride levels, the composition of lipoproteins shifts, and the traditional calculation no longer reflects reality; thus, the accuracy is compromised.

Therefore, the maximum triglyceride level for which the Friedewald formula is considered valid is indeed a threshold of 400 mg/dL.