How do you calculate non-HDL cholesterol?

Laboratory analysis directly measures HDL, triglycerides and total cholesterol, and these values are used to indirectly determine LDL using the Friedewald equation: LDL = total cholesterol - HDL - (triglycerides/5), according to About.com. There are four components to total cholesterol: HDL, LDL, VLDL and triglycerides.

In cases where triglycerides are very high, above 400 milligrams per deciliter, the Friedewald equation may not be accurate, and additional lipid profile testing is performed to directly measure LDL levels, states About.com. VLDL is determined indirectly as a percentage of the triglyceride value, but it is often not reported during routine cholesterol screening, according to the Mayo Clinic.