Given the lipid results Total cholesterol 400 mg/dL; triglycerides 300 mg/dL; HDL-C 100 mg/dL, what is the LDL-C?

• A. 240 mg/dL
• B. 160 mg/dL
• C. 200 mg/dL
• D. 300 mg/dL

Answer: (A)

The calculation uses the Friedewald equation: LDL-C = total cholesterol − HDL-C − (triglycerides/5), valid when triglycerides are under 400 mg/dL and the patient is fasting. Here, triglycerides are 300 mg/dL, so triglycerides/5 = 60 mg/dL. Then LDL-C = 400 − 100 − 60 = 240 mg/dL. So the LDL-C is 240 mg/dL. This method is appropriate because TG is below the 400 mg/dL threshold; if TG were higher, the equation wouldn’t be reliable and direct LDL measurement or alternative calculations would be needed.