Toxicology: choice of EDTA salt: practice question

A Forensic Medicine 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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Forensic Medicine · Toxicology: choice of EDTA salt

Sample item

A nurse has two vials, disodium EDTA and calcium disodium EDTA, for a child with lead poisoning. Which should be used, and why?

ACalcium disodium EDTA, because disodium EDTA binds serum calcium and can cause fatal hypocalcaemiaBEither, since the two salts are equivalentCDisodium EDTA, because sodium enhances renal excretion of leadDNeither, since only succimer can chelate lead

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

The answer and the reasoning

A. Calcium disodium EDTA, because disodium EDTA binds serum calcium and can cause fatal hypocalcaemia

Calcium disodium EDTA exchanges its calcium for lead, forming a soluble complex excreted in urine. Disodium EDTA lacks the calcium and removes the patient's own ionised calcium, causing tetany, arrhythmia and death. It is given with dimercaprol in lead encephalopathy.

Option by option

A. Calcium disodium EDTA, because disodium EDTA binds serum calcium and can cause fatal hypocalcaemia (correct)
Correct. The calcium salt avoids profound hypocalcaemia.
B. Either, since the two salts are equivalent
The salts are not interchangeable because of the hypocalcaemia risk.
C. Disodium EDTA, because sodium enhances renal excretion of lead
Sodium has no role in lead excretion, and this salt is dangerous.
D. Neither, since only succimer can chelate lead
EDTA is an effective lead chelator, and succimer is not the only option.

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.

Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is A, Calcium disodium EDTA, because disodium EDTA binds serum calcium and can cause fatal hypocalcaemia. Calcium disodium EDTA exchanges its calcium for lead, forming a soluble complex excreted in urine.

Why is "Either, since the two salts are equivalent" not the answer?

The salts are not interchangeable because of the hypocalcaemia risk.

Why is "Disodium EDTA, because sodium enhances renal excretion of lead" not the answer?

Sodium has no role in lead excretion, and this salt is dangerous.

Why is "Neither, since only succimer can chelate lead" not the answer?

EDTA is an effective lead chelator, and succimer is not the only option.

What concept does this question test?

It tests Toxicology: choice of EDTA salt in Forensic Medicine. Disodium EDTA lacks the calcium and removes the patient's own ionised calcium, causing tetany, arrhythmia and death. It is given with dimercaprol in lead encephalopathy.

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 Toxicology: choice of EDTA salt?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.