ADH question

[Radon]

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hey guys

i have a q Re: Central DI vs. Neurogenic DI vs. psychogenic...i'm obviously missing something...

in Goljan's notes it says that:

#1 = Posm post-water deprivation (NML: 292)
#2= Uosm post-water deprivation (750)
#3= Uosm post-ADH injection "(760)

For CDI: 319 110 550
NDI: 312 98 120
Psych: 288 760 780

my questions....
1. AFTER-ADH administration why would Uosm change in NDI if, as i understand, NDI is due to renal insensitivity to ADH?? And wouldnt CDI be corrected w/ ADH, or is 550 "good enough" ?
2. in psycho, why is the Uosm incr...it seems that if u drink a lot of water the urine is going to be diluted...i.e. hyposomotic not hyper...

please help!!!.....thanks

 

[Radon]

I guess everyone is on vacation huh? anyone out there?

 

[Idiopathic]

to answer your 1st question, the criteria in differentiating CDI from NDI after a water-deprivation test is to administer ADH and look for a 50% rise in UOsm. In NDI, the UOsm may fluctuate just a little, but since it does not go up by 50%, it is definitely NDI.

in psychogenic polydipsia, since the kidneys are fine, administration of ADH will be handled by the kidneys just as it normally would, pulling back all the free water it can. dont overthink the kidney, it can hurt.

 

[Radon]

Thank you!!!