In indirect calculation of LDL-C, which set of values is required?

• A. Total Cholesterol, HDL, and TAG
• B. Total Cholesterol, HDL, and LDL
• C. Total Cholesterol, VLDL, and HDL
• D. HDL, TAG, and VLDL

Answer: (A)

In indirect LDL-C calculation, you estimate the LDL cholesterol from the other lipid values using the Friedewald equation: LDL-C ≈ Total cholesterol − HDL-C − (triglycerides/5) in mg/dL. This means you need three inputs: total cholesterol, HDL cholesterol, and triglycerides. The triglycerides are divided by 5 to approximate the amount of VLDL cholesterol, which is then subtracted along with HDL-C from total cholesterol to yield the LDL-C.

So the required set is total cholesterol, HDL, and triglycerides. The other sets either replace triglycerides with VLDL (which isn’t measured directly in this method) or involve LDL as an input (LDL is the result, not an input), so they don’t fit this indirect approach. Note that the calculation is valid only when triglycerides are below about 400 mg/dL and the sample is suitable for this estimation.