Common method used for the estimation of LDL cholesterol

Even though the 'Direct Estimation Methods' are more accurate and precise than the conventional methods,(ie Precipitation method for HDL-Cholesterol & Friedewald's formula for LDL-Cholesterol.)the direct methods are not commonly used by clinical laboratories because it is expensive, time consuming, and it requires equipment not commonly available in the clinical lab.

Friedwald’s Formula:It is the conventional method for the estimation of LDL-cholesterol in fasting specimen

The formula

LDL-cholesterol = Total cholesterol - HDL cholesterol - VLDL

VLDL=TRIGLYCERIDES /5


Limitation of Friedwald's formula

Friedewald formula is unreliable in the presence of chylomicronemia ,hypertriglyceridemia (when plasma triglyceride concentration exceeds 400 mg/dL or 4.52 mmol/L) and in patients with dysbetalipoproteinemia (type III hyperlipoproteinemia).

Further reading

http://www.clinchem.org/cgi/content/full/43/11/2183