Lipid profile: Friedewald calculation: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Lipid profile: Friedewald calculation

Sample item

A fasting lipid profile shows total cholesterol 260 mg/dL, HDL cholesterol 40 mg/dL and triglycerides 150 mg/dL. Using the Friedewald equation, what is the calculated LDL cholesterol?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. 190 mg/dL

The Friedewald equation estimates LDL as total cholesterol minus HDL minus triglycerides divided by 5, the last term approximating VLDL cholesterol. Here VLDL is 150 divided by 5, which is 30. LDL is therefore 260 minus 40 minus 30, which is 190 mg/dL. The equation is invalid if triglycerides exceed 400 mg/dL.

Option by option

  • A. 230 mg/dL

    230 results from subtracting VLDL but forgetting to subtract HDL.

  • B. 220 mg/dL

    220 is total cholesterol minus HDL only, which is non-HDL cholesterol, and it forgets to subtract VLDL.

  • C. 70 mg/dL

    70 results from subtracting the whole triglyceride value rather than one fifth of it.

  • D. 190 mg/dL (correct)

    The arithmetic is 260 - 40 - 30 = 190 mg/dL.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, 190 mg/dL. The Friedewald equation estimates LDL as total cholesterol minus HDL minus triglycerides divided by 5, the last term approximating VLDL cholesterol.

Why is "230 mg/dL" not the answer?

230 results from subtracting VLDL but forgetting to subtract HDL.

Why is "220 mg/dL" not the answer?

220 is total cholesterol minus HDL only, which is non-HDL cholesterol, and it forgets to subtract VLDL.

Why is "70 mg/dL" not the answer?

70 results from subtracting the whole triglyceride value rather than one fifth of it.

What concept does this question test?

It tests Lipid profile: Friedewald calculation in Biochemistry. Here VLDL is 150 divided by 5, which is 30. LDL is therefore 260 minus 40 minus 30, which is 190 mg/dL. The equation is invalid if triglycerides exceed 400 mg/dL.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Lipid profile: Friedewald calculation?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.