SIADH and urine specific gravity

Hi all,

I'm sure this is really obvious but I can't get my head around it and can't find the answer/explanation anywhere I search....
Why/how does the urine specific gravity go up in SIADH?? In my head it should go down because the urine would be more diluted due to less water output. I know this is wrong but can't work out why?!

Thanks,
Jill
Quote from JillNasWhy/how does the urine specific gravity go up in SIADH?? In my head it should go down because the urine would be more diluted due to less water output.

What is specific gravity (SG)? What does it tell you about a solution (such as urine)? If SG is very close to 1 what does this mean about the solute content of the urine? If it is higher (what would a high SG for urine be?), what does it tell you about the solute content of the urine?So, what happens in the kidney with SIADH? What can you then say about the nature of the urine--specifically solute content of the urine? Given that solute content, what would you expect the SG to be?What about the opposite of SIADH? What is this condition called? What would SG be here?

Ha, of course!! I was (stupidly) thinking of the fluid in the body instead of excreted urine. I knew it was something simple. Thank you!!

Good answer, get me thinking! I have it straight in my head now. I was having a really silly mind block. Thank you

Oh great. Now I have got a question on Kaplan regarding low sodium (122) and low specific gravity (1.008) and the answer states that it is due to SIADH, which "results in increased water absorption and dilutional hyponatremia". But the specific gravity should be high!?!?!

The only way I can make sense of a low specific gravity in the presence of SIADH is if they're actually talking about the blood's specific gravity rather than the urine's. However, I did find this old thread: http://allnurses.com/nursing-student...ic-385300.html that may offer a more reasonable explanation.

Quote from JillNasOh great. Now I have got a question on Kaplan regarding low sodium (122) and low specific gravity (1.008) and the answer states that it is due to SIADH, which "results in increased water absorption and dilutional hyponatremia". But the specific gravity should be high!?!?!