Question

Consider the following statements: In nephrogenic diabetes insipidus, the patient is likely to have
1. High vasopressin level.
2. Poor or no response to desmopressin.
3. Low plasma osmolality.
4. Elevated plasma glucose level.
Which of these statements are correct?

• A. 1, 2 and 3
• B. 2, 3 and 4
• C. 1 and 4
• D. 1, 2, 3 and 4

Hint:

NDI raises vasopressin but the kidney tubules will not respond to it.

Answer 1

The Correct Option is A

Nephrogenic diabetes insipidus (NDI) means the collecting ducts of the kidney do not answer the call of vasopressin, even though the hormone is present in normal or high amounts.

1. High vasopressin level: True. Since the kidney cannot concentrate urine, the body keeps losing water, the plasma gets slightly more concentrated, and this pushes the pituitary to release more vasopressin. So plasma vasopressin runs high in NDI, unlike central DI where it runs low.
2. Poor or no response to desmopressin: True, and this is the classic test used at the bedside. Give desmopressin: central DI patients concentrate their urine because they were simply short of hormone, while NDI patients show little change because their kidney tubules cannot respond regardless of how much hormone is supplied.
3. Low plasma osmolality: This does not match NDI as literally worded. The real finding is low urine osmolality (dilute urine), while plasma osmolality tends to run high, not low, because the patient keeps losing free water. This looks like a transcription error in the original statement, most likely meant to say urine osmolality.
4. Elevated plasma glucose level: False. This belongs to diabetes mellitus, an unrelated disease that only shares part of its name with diabetes insipidus.

Only statements 1 and 2 hold up cleanly as true features of NDI. None of the four listed option combinations gives exactly 1 and 2 only. Between the two options containing both 1 and 2, '1, 2 and 3' is the better fit, since statement 3 is at least arguably true under a charitable reading, unlike statement 4 in the other option, which is clearly false.

Let's summarize:

• High vasopressin level and poor response to desmopressin are the two solid, textbook features of nephrogenic DI.
• The statement about low plasma osmolality is most likely a wording slip for low urine osmolality, and elevated glucose has nothing to do with this condition.

Because none of the given combinations correctly isolates just statements 1 and 2, '1, 2 and 3' is taken as the best available answer among the flawed options.