Clinical enzymology: LDH isoenzymes: 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 · Clinical enzymology: LDH isoenzymes

Sample item

A 58-year-old man presents 3 days after an episode of prolonged chest pain. Electrophoresis of serum lactate dehydrogenase is requested. Which pattern supports a recent myocardial infarction?

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

The answer and the reasoning

C. LDH1 greater than LDH2, the flipped pattern

The heart is rich in the H4 isoenzyme LDH1, which is released after myocyte necrosis and rises within about 24 to 48 hours, so LDH1 exceeds LDH2 (normally LDH2 is higher). LDH5 rises in liver and skeletal muscle injury. Troponin has replaced LDH for diagnosis, but the flipped pattern remains a classic late marker.

Option by option

  • A. Isolated rise of LDH3

    LDH3 predominance suggests pulmonary or lymphoid disease rather than cardiac injury.

  • B. LDH5 greater than LDH4

    A predominant LDH5 band points to hepatic or skeletal muscle damage.

  • C. LDH1 greater than LDH2, the flipped pattern (correct)

    Correct. Release of cardiac LDH1 reverses the normal LDH2 to LDH1 relationship.

  • D. LDH2 greater than LDH1 with raised LDH3

    This is close to the normal pattern, with LDH3 reflecting lung or lymphoid tissue.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, LDH1 greater than LDH2, the flipped pattern. The heart is rich in the H4 isoenzyme LDH1, which is released after myocyte necrosis and rises within about 24 to 48 hours, so LDH1 exceeds LDH2 (normally LDH2 is higher).

Why is "Isolated rise of LDH3" not the answer?

LDH3 predominance suggests pulmonary or lymphoid disease rather than cardiac injury.

Why is "LDH5 greater than LDH4" not the answer?

A predominant LDH5 band points to hepatic or skeletal muscle damage.

Why is "LDH2 greater than LDH1 with raised LDH3" not the answer?

This is close to the normal pattern, with LDH3 reflecting lung or lymphoid tissue.

What concept does this question test?

It tests Clinical enzymology: LDH isoenzymes in Biochemistry. LDH5 rises in liver and skeletal muscle injury. Troponin has replaced LDH for diagnosis, but the flipped pattern remains a classic late marker.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Clinical enzymology: LDH isoenzymes?

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.