Low Specific Gravity

[BigD]

Hi there - anyone out there have any experience with a Low specific gravity in urine? My 12 week old pup had some sort of urinary infection which was treated 4 weeks ago (for 2 weeks). She seemed to improve and today we took in a sample (not a clean one mind you) and it tested for more bugs. She also had a low specific gravity on both urine tests.

 

The vet was concerned - I guess that can make it easier for the bugs to live in the urine. So he said that we could do blood work around 6 months to check for kidney issues. I asked if we could do it now - to check now and have a base line for future anyway. He said sure. I get results tomorrow.

 

I did a quick look on the web for this issue and something came up called Fanconi syndrome. Sounds nasty. Sounds bad. So I'm hoping this could be an issue just since she is:

1. young

2. Plays a lot and thus drinks a lot

3. The urine sample was not a first thing in the morning, it was an hour and a half after she woke up and did some play/eating

4. Something that will improve with time.

 

Basically, hold my hand and tell me it will be ok...that's what i'm looking for. The vet will call me tomorrow with results. She does drink a lot, but she plays a lot too. It's been hot here - especially when she first came to us. She will drink and drink when she plays and then have to pee within 30 to 40 minutes afterwards. She would wet herself in her sleep when she was younger (8-10 weeks) but hasn't done that in a long time.

 

Waa! I hate this waiting crap...ugh...

 

The vet did say to NEVER with hold water from a dog. Period. I'm going to post on the other thread about water in crate. He says you can do some kidney damage this way. Heck, I agree!

 

Ok, going to try and work, work to get my mind off of this.

 

Denise

[AK dog doc]

How low is "low"?

 

Adult dogs I usually like to see at 1.020 or higher. Puppies can't concentrate their urine as well so I don't worry if they're lower for a while. a specific gravity of 1.010 is not concentrated at all ("isosthenuric") - it's the same concentration as the fluid in the bloodstream. Below 1.010 is "hyposthenuric", meaning the urine is LESS concentrated that what you'd expect the blood to be (in an adult dog - puppies are more water per pound of dog than adults are.) This can happen if the dog is drinking excessive amounts of water for whatever reason (mental or physical).

 

Dilute urine can be because the dog drinks excessively (polydipsia) and then the body urinates extra in trying to dump extra fluid; or because the kidney is unable to concentrate the urine in order to conserve fluid (polyuria) and so the dog drinks excessively in order to keep up with fluid loss. So excessive drinking can cause excessive (and dilute) urine, or excessive (and dilute) urine can cause excessive drinking. Chicken-or-egg dilemma.

 

There are a lot of possible causes for dilute urine - kidney problems are one, but only one. There are reasons the dog might not concentrate its urine even if the kidney tissue is 100% normal and healthy - one is a lack of or failure of response to a hormone called ADH, which tells the kidney to concentrate the urine. The kidney is just fine, but no one is telling it to concentrate the urine, so it doesn't (this is called diabetes insipidus, not to be confused with the more farmilliar diabetes mellitus, which used to be called "sugar diabetes".) This can occur due to a lack of ADH production (rare, except with alcohol intake - why you pee a lot when you drink) or a failure to respond to the ADH (like when you have caffiene, or with certain types of bacterial infection, which block the ADH receptor and prevent it from signalling the kidney to concentrate the urine.)

 

Another cause is called renal medullary washout. to explain this, I'll back up a moment, and sorry if this is redundant (so many of the folks here are well-educated, I don't know whch ones have which info, so I'm not trying to insult anyone's intelligence here)...

 

Remember in high school bio when you talked about osmosis? To recap, fluid will cross a semi-permeable membrane in such a way as to make the concentration of solutes the same on either side of the membrane. So if you have, say, 100 salt molecules per ml on one side and only 10 on the other, water will move over from the 10 side to the 100 side until both sides have the same concentration. In the renal medulla (which is the inner layer of the kidney), there is a salt gradient that helps concentrate the urine by osmosis. If that salt gradient gets washed away, osmosis doen't help concentrate the urine, because each side of the membrane is at 10 (for example), so no fluid moves out of the urine and back into the body to be saved. There is nothing at all wrong with the cells or tissues of the kidney - it's just an absence of appropriate salt concentrations.

 

One of the ways you wash out the gradient is by excessive drinking (here I'm talking water! ), which puppies do a lot of anyway, especially if they have a kidney infection. That may persist until they rebuild the salt gradient. There IS a medical indication to withhold water (called a water deprivation test) but it's done in a special cage called a metabolic cage, and the patient's blood osmolality (the concentratin of things in the blood) is carefully monitored and not allowed to go over a certain level. Realistically this is usually done at a university or a specialty hospital. In the absence of that, you really shouldn't withold water on a puppy, especially one with a UTI.

 

So, that was a lot of info to basically let you know that a low specific gravity is not necessarily an indicator of something wrong with the kidney - it MIGHT be, but there are a lot of other possibilities. I don't suppose telling you not to worry will make you not worry, though. Meantime, cut out all the alcohol and caffiene in the puppy's diet and at least TRY not to worry. Fanconi's syndrome is pretty rare, so not very likely. (I've never seen one, but I've seen lots of renal medullary washouts from infection, shock, primary polydipsia, etc., so odds are against Fanconi's just based on the numbers.)

[BigD]

Hi AK Dog doc -

 

We did another test on Marzipan's urine. She's now 1024. I don't remember where the decimal went, but it was 1024. She's about 15 weeks now.

 

At 12 weeks - she was 1015, at 9 weeks she was 1012.

 

We had blood work done at 12 weeks and didn't find anything specific. The vet says he likes to see dogs at 1030. But admits that 1024 is better than 1012 and 1015. He wants us to retest in a few months - to make sure she stays at this level or above - around the 1030 is what he would like.

 

You say - 1020 is where you like to see the adults, so is my vet just being over protective - which is fine with me! I'm glad she's getting better...just curious what you think.

 

Thanks a bunch - hope you are keeping warm. Still hasn't gotten cold enough here to close the windows...

 

Denise

[AK dog doc]

Still keeping warm, though there's a knife-edged breeze out tonight, so I'm staying in (dark by now anyway, and my headlamp is out of bateries, which makes night skiing hazardous, what with moose and snowmachiners in varying stages of inebriation and so on...)

 

On the specific gravity, I like to see adults at 1020 *or higher* - 1020 is the low end of what I'd consider to be normal (assuming it's persistent). (As a BTW, the decimal goes after the first "1" - so, 1.020, but by convention we all tend to say "ten-twenty" since it's WAAAAAAY too hard for us to force ourselves to say "one point oh two oh". We might forget what we were talking about by the time we get through all that.)

 

I'll stick with my premise that pups cannot concentrate their urine as well as adults, so I'd probably be pretty comfortable with a 1024 on a pup less than 4 months old. Remember that 1010 is not concentrated at all - so even at 1012 and 1015 she WAS concentrating her urine, just not very much. I'd be okay with that in a puppy if everything else was looking good and there were no clinical signs of trouble, but I would expect that to come up a bit as the pup matures - it would be too low for an adult.

 

So yes, I think your vet is maybe being a teeny bit overprotective, but that's generally a good trait in a vet, IMO, and I don't think you should try to talk him out of it! Everyone has their own comfort zone, and if his is at 1030, that's fine; for me, I'm cool with 1020 or better, since low end of normal is still *normal*, and I expect some fluctuation here and there. So in a pup Marzipan's age, I'd be fine with a 1020 specific gravity. JMO.