Calculate the LDL cholesterol given total cholesterol 250 mg/dL, HDL 40 mg/dL, and triglycerides 210 mg/dL (use Friedewald equation).

Calculate the LDL cholesterol given total cholesterol 250 mg/dL, HDL 40 mg/dL, and triglycerides 210 mg/dL (use Friedewald equation).

• A. 120 mg/dL
• B. 168 mg/dL
• C. 210 mg/dL
• D. 95 mg/dL

Answer: (B)

LDL cholesterol is estimated by subtracting HDL-C and a VLDL-C estimate from total cholesterol. In the Friedewald equation, VLDL-C is approximated as triglycerides divided by 5 when triglycerides are expressed in mg/dL and are under about 400 mg/dL. So, VLDL-C = 210/5 = 42 mg/dL. Then LDL-C = 250 − 40 − 42 = 168 mg/dL. This is valid here because the triglycerides are 210 mg/dL (below 400) and the calculation uses mg/dL. If triglycerides were ≥400 mg/dL, the Friedewald estimate becomes unreliable and a direct LDL measurement would be preferred. The numbers given thus yield 168 mg/dL, matching the correct result.

LDL cholesterol is estimated by subtracting HDL-C and a VLDL-C estimate from total cholesterol. In the Friedewald equation, VLDL-C is approximated as triglycerides divided by 5 when triglycerides are expressed in mg/dL and are under about 400 mg/dL. So, VLDL-C = 210/5 = 42 mg/dL. Then LDL-C = 250 − 40 − 42 = 168 mg/dL. This is valid here because the triglycerides are 210 mg/dL (below 400) and the calculation uses mg/dL. If triglycerides were ≥400 mg/dL, the Friedewald estimate becomes unreliable and a direct LDL measurement would be preferred. The numbers given thus yield 168 mg/dL, matching the correct result.