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NBME 20 Answers

nbme20/Block 2/Question#34

A 28-year-old man has excessive thirst and ...


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submitted by sugaplum(86),

These always tripped me up:
+ Polydipsia= responds to water deprivation, low serum Na
+ Central= responds to vasopressin, high serum Na
+Nephrogenic = responds to nothing, normal serum Na

lynn  I think serum Na+ only depends on the patient's access to water. FA19 pg 344 says serum osm is high in both and doesn't mention Na specifically. Spent a while double checking for DI, but low serum Na for polydipsia is definitely correct. +  

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submitted by hayayah(525),

Pt has diabetes inspidus.

If urine concentrates with administration of ADH analog, the kidneys are responsive and the problem is with ADH production in the hypothalamus or release in the post. pituitary.