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

Step 1: Understanding the Question.
We need to sort out which features truly belong to nephrogenic diabetes insipidus (NDI), a condition where the kidney tubules do not respond properly to the hormone vasopressin (ADH).

Step 2: Key Concept.
In NDI the problem sits at the kidney, not the pituitary. The pituitary keeps releasing vasopressin normally, but the collecting duct cells fail to respond to it, so the urine stays dilute no matter how much hormone is around. This is the opposite of central diabetes insipidus, where the pituitary itself makes too little vasopressin.

Step 3: Detailed Explanation.
Statement 1, high vasopressin level, is a true and well known feature of NDI. Because the kidney cannot concentrate urine, the body keeps losing free water, and the osmoreceptors respond by driving the pituitary to release more vasopressin, so plasma vasopressin runs high, not low as it would in central DI. Statement 2, poor or no response to desmopressin, is also true and is in fact the standard bedside test used to tell NDI apart from central DI. Central DI improves after a desmopressin dose because the drug supplies the missing hormone, while NDI shows little to no improvement because the kidney tubule itself is unresponsive. Statement 4, elevated plasma glucose, is not a feature of NDI. Blood glucose belongs to diabetes mellitus, a completely different disease that only shares the word diabetes with DI, and it is placed here as a distractor. Statement 3, low plasma osmolality, is the confusing part of this question. What NDI actually gives you is a low urine osmolality, since the urine cannot be concentrated, while plasma tends to run high or high normal in osmolality if the patient cannot keep up with the water loss. Taken word for word, low plasma osmolality does not fit NDI, and this is most likely a copying slip in the original question for what should read urine osmolality. Because of this defect in the statement itself, no combination among the four options exactly matches only the two statements that are cleanly true, statements 1 and 2. Of the two options that include both 1 and 2, option '1, 2 and 3' is the closer fit, since it only adds the flawed statement 3 (arguably true if read as urine rather than plasma osmolality), while the other such option also drags in the clearly false statement 4.

Step 4: Final Answer.
Statements 1 and 2 are the features that are clearly and reliably true of nephrogenic diabetes insipidus. Statement 3 is only correct if read as low urine osmolality rather than plasma osmolality, and statement 4 is false. Because of this wording issue, no option cleanly fits, but '1, 2 and 3' is the best available fit among the four choices.