Feline Urine Specific Gravity

RE: Feline Urine Specific Gravity

Lucy Fleming — Mon, 07 Dec 2015 12:19:25 GMT

[quote user="Shoshannah McCarthy"]I think I'm going to have to measure my cat's USG just to see if it's over 1.035, dammit! >.<[/quote]

Would you? I'd love to know! (Genuinely :-))

RE: Feline Urine Specific Gravity

Anthony Todd — Wed, 02 Dec 2015 22:41:08 GMT

[quote user="Shoshannah McCarthy"]I think I'm going to have to measure my cat's USG just to see if it's over 1.035, dammit[/quote]

Factor in the diet and prawn water or you may worry unnecessarily

[see what I mean about worrying owners!!]

RE: Feline Urine Specific Gravity

Shoshannah McCarthy — Wed, 02 Dec 2015 20:09:21 GMT

I think I'm going to have to measure my cat's USG just to see if it's over 1.035, dammit! >.<

RE: Feline Urine Specific Gravity

Anthony Todd — Wed, 02 Dec 2015 16:33:48 GMT

[quote user="Thomas Johnson"]But what were the specific gravities? Cats on dry food often have a USG of 1.060, and I suspect cats on wet food have a USG of at least 1.040, so significantly lower, but still over 1.035.[/quote]

I can't copy and paste the table from the paper but quoting from it, and much to my surprise, these are the relevant bits which others with the paper can confirm:

"Characteristics of 949 apparently healthy adult cats Age 0.6-21, SG median 1.050 (1.005-1.090)

Young cats Age 0.15- 0.45 median 1.050 (1.017-1.080)"

I don't think I've seen any urine anywhere at 1.090??? [bet it was on very very dried food!!]

and 1.005 must have been on lots and lots of prawn water

RE: Feline Urine Specific Gravity

Thomas Johnson — Wed, 02 Dec 2015 15:50:47 GMT

[quote user="Anthony Todd"]

Just this from the cited paper:

Investigators have found that cats fed canned (highmoisture)
diets consume more total water (through food
and drinking) and have lower USGs than cats consuming
dry diets.2,10–13 Similarly, the USG in healthy male adult
cats decreased after oral water loading with 4–10 ml/kg
of water.4

[/quote]

But what were the specific gravities? Cats on dry food often have a USG of 1.060, and I suspect cats on wet food have a USG of at least 1.040, so significantly lower, but still over 1.035.

RE: Feline Urine Specific Gravity

Anthony Todd — Wed, 02 Dec 2015 14:34:24 GMT

Just this from the cited paper:

RE: Feline Urine Specific Gravity

Danny cazabon — Wed, 02 Dec 2015 13:17:31 GMT

Idexx have a new SDMA biomarker for kidney function. Able to detect changes at 40% functional nephron loss. Out next month. At 60% functional nephron loss we see a lower USG so if a renal cat, it should be supported with new biomarker test.

RE: Feline Urine Specific Gravity

Glen McIntosh — Wed, 02 Dec 2015 11:50:29 GMT

[quote user="Anthony Todd"]There is no such thing as a 'normal' USG without context.[/quote]

While that is certainly true, I think we are getting bogged down on the wrong context.

I think that most people would agree that USG should be interpreted in the context of a cat's hydration status, not its type of diet or water intake.

For example, a normal cat that is dehydrated (for reasons other than disease) will have a very high USG.

A normal cat that has normal hydration will have an sg > 1.035 in most cases.

A normal cat that is over-hydrated will have a lower than normal SG.

This will be true no matter what the normal cat is eating or drinking.

Normal cats will tend towards homeostasis with regard to hydration status, as is true for all physiological systems.

A normal cat, eating wet canned food and drinking prawn juice will simply drink less water to avoid becoming over hydrated. A normal cat, eating only dry food will drink comparatively more water to avoid dehydration. Both will have a normal SG (>1.035).

A normal cat being force fed water by its owner will become overhydrated and its SG will fall in order to maintain homeostasis.

In the cat with renal disease, it will almost always be dehydrated. SG will be lower because of the disease and it will stay lower even though it is dehydrated and it will stay dehydrated even if it drinks more.

RE: Feline Urine Specific Gravity

Thomas Johnson — Mon, 30 Nov 2015 18:01:04 GMT

[quote user="Anthony Todd"]

But he already is in the 100% wet food!

His SG will almost certainly be < 1.030 too, but he is normal!

If you gave him a treat of boiled prawn water, as well, he would drink even more and his SG would be even lower, but still totally irrelevant as far as renal disease is concerned.

[/quote]

And I think this is where the big disagreement comes in, I think a normal cat on wet food will have a USG of over 1.035. If the owners are adding extra water to its diet then yes, this will lower its SG, but they're only likely to do be doing that if we've told them to. And giving a treat of cat milk or flavoured water will also lower they're SG, but from my conversations with owners about diet I think very few owners are doing this.

RE: Feline Urine Specific Gravity

Anthony Todd — Mon, 30 Nov 2015 17:45:40 GMT

[quote user="Kate Richardson"]You reckon?[/quote] etc.

Last word.

A SG of < 1.035 in an otherwise healthy and well cat is unusual and warrants monitoring and/or further investigations, if it is on a dry diet but with water available.

As so many cats now are on exactly that, so, because of that, you are quite right.

RE: Feline Urine Specific Gravity

Kate Richardson — Mon, 30 Nov 2015 16:53:21 GMT

[quote user="Anthony Todd"]

But he already is in the 100% wet food!

His SG will almost certainly be < 1.030 too, but he is normal!

[/quote]

You reckon? I would bet that it's more likely than not >1.035 despite his diet (as the study Shoshannah McCarthy has highlighted has shown

and I also bet that if it is less than 1.035 Shoshannah would be repeating it and monitoring it.

No where that I can see has anyone said that an SG of <1.035 is 100% diagnostic of renal disease in cats. Personally I have simply tried to suggest to you that an SG of < 1.035 in an otherwise healthy and well cat is unusual and warrants monitoring and/or further investigations and I think this study backs that up. Informing an owner that this USG is unusual and MAY indicate an underlying problem is not alarming them unnecessarily; possibilities are discussed and a plan is made- this may be simply doing nothing and rechecking the USG in 1 months time to see if repeatable and therefore IF further investigations are justified. If owner's consent to a test eg urinalysis in the first place (for whatever reason) then it is surely our job to report any anomalies and advise further. At least that's my take on it.

Bored now

RE: Feline Urine Specific Gravity

Anthony Todd — Mon, 30 Nov 2015 11:35:52 GMT

[Sorry turbo-posting, and, Arlo, block me if you like, but why don't others get it?]

[quote user="Shoshannah McCarthy"] I don't think he's one for taking in or excreting any unnecessary extra water.[/quote]

But he already is in the 100% wet food!

His SG will almost certainly be < 1.030 too, but he is normal!

If you gave him a treat of boiled prawn water, as well, he would drink even more and his SG would be even lower, but still totally irrelevant as far as renal disease is concerned.

There is no such thing as a 'normal' USG without context.

As someone much smarter than me has already said.

You could be alarming owners unnecessarily by flagging a low USG.

RE: Feline Urine Specific Gravity

Shoshannah McCarthy — Mon, 30 Nov 2015 00:40:49 GMT

This one was in JFMS earlier this year:

http://m.jfm.sagepub.com/content/17/4/329

1040 healthy cats had their USG measured by refractometry. It was >1.035 in 88% of the cats.

Only 126 of those 1040 had a USG under 1.035. Of those, only 48 had no medical cause identified (27 did, and 51 weren't worked up so we don't know either way).

This study has its limitations, which become apparent if you read the whole paper, but taken at face value these figures suggest that only 48 of 1040 cats (that's less than 5%) had a USG of <1.035 while definitely being free of identifiable pathology. I guess this is why seeing a USG of <1.035 can be worrying - especially in an older cat.

Diet type (wet or dry), sex, fasting status etc were variable and no factor greatly affected USG, though increasing dietary moisture decreased USG only in the female cats (I can't explain that and neither could the authors; I'm doubtful of the reliability significance of that result).

Moving onto anecdotal evidence, I virtually never see my cat drink. Maybe once every few months? He is on 100% wet food. His need to take in fluid beyond that consumed in his diet is obviously small to nil. He pees once or twice a day, I don't think he's one for taking in or excreting any unnecessary extra water... but this is highly unscientific and I haven't actually measured his USG - perhaps I should!

RE: Feline Urine Specific Gravity

Martin Atkinson — Fri, 27 Nov 2015 19:22:44 GMT

[quote user="Kate Richardson"]For example, for both of our most commonly used external labs (and in-house machines) the upper part of the normal creatinine ref range would be considered elevated according to IRIS guidelines.[/quote]

[quote user="Kate Richardson"]I know what you mean. But there are plenty of people who I respect who have endorsed these values. I'm not sure why labs haven't changed their ref ranges or added info to say for example if creat less than 140 no worries, 140-180 monitor/reassess/check USG, >180 abnormal.[/quote]

This is why I believe you have to consider BUN. The IRIS guidelines suggest that a cat has stage 1 CKD with a creatinine of <140 which is perfectly normal for a erm... normal cat and 140-249 for stage 2 the lower end of which is still normal. Now I know that sarcopenic old cats should be expected to have a lower creatinine but it doesn't say in the IRIS guidelines that is necessarily the case nor does it give a break-even point on body score. Admittedly they do not say an animal needs to have a raised BUN, and azotaemia by definition is an increase in any protein containing compound which could be BUN or creatinine. So what criteria do you use to determine that a cat with a creatinine of <140 is still in stage 1 CKD. Mine has always been that there is an azotaemia due to raised BUN even if its just one notch over normal but am I now to use only a USG of <1.030 to determine this?

RE: Feline Urine Specific Gravity

Anthony Todd — Fri, 27 Nov 2015 16:20:31 GMT

[quote user="Martin Atkinson"]Time to put a cap on it I think Anthony.[/quote]

I agree, it's pretty obvious so why is it, apparently misunderstood?

RE: Feline Urine Specific Gravity

Martin Atkinson — Fri, 27 Nov 2015 16:00:59 GMT

[quote user="Anthony Todd"]

But, surely if the cat was drinking more than it's metabolic needs by drinking loads of milk, sloppy food, or boiled prawn water, which they love, it would pass loads of urine, with a low SG otherwise how do they get rid of all that unnecessary water?

This has been my point all along!

[/quote]

I thought there was a new rule on turbo posting. Time to put a cap on it I think Anthony.

RE: Feline Urine Specific Gravity

Anthony Todd — Fri, 27 Nov 2015 14:32:57 GMT

[quote user="Lucy Fleming"] I would tend to say that a cat on a moist diet still ought to be producing concentrated urine, and if a urine sample was isosthenuric I would want to at least repeat it and preferably follow it up with a blood sample.[/quote]

This has been my point all along!

Sure. cats on dried food, and only drinking their metabolic water needs, will pass the minimum volume of urine with the maximum SG.

This is what most posters have assumed and, if on dried food and just metabolic water intake, a low SG will be highly significant 'cos the SG should be at the max.

RE: Feline Urine Specific Gravity

Lucy Fleming — Fri, 27 Nov 2015 12:39:21 GMT

[quote user="Anthony Todd"]You should read the posts again, from the beginning[/quote]

I did read them all, from the beginning. When isosthenuric urine is being discussed, it is in the context of a cat that is azotaemic and/or dehydrated and therefore should be producing concentrated urine, regardless of how much water is in their food. I would tend to say that a cat on a moist diet still ought to be producing concentrated urine, and if a urine sample was isosthenuric I would want to at least repeat it and preferably follow it up with a blood sample.

RE: Feline Urine Specific Gravity

Anthony Todd — Fri, 27 Nov 2015 09:48:33 GMT

[quote user="Lucy Fleming"]no they aren't[/quote]

You should read the posts again, from the beginning, and note the weight given to urine SG without any consideration of water intake via diet or water content of food.

Creatinine and BUN are given licence to be variable; SG is given none [until the last page].

RE: Feline Urine Specific Gravity

Lucy Fleming — Thu, 26 Nov 2015 21:31:20 GMT

[quote user="Kate Richardson"]there are plenty of people who I respect who have endorsed these values[/quote]

I didn't mean to suggest I didn't agree with the values! I also find it a bit frustrating that the lab hasn't changed their ref ranges at all - if only because I have to look them up from a second source.

[quote user="Kate Richardson"]With regard to UPC, as far as I am aware < 0.2 = normal, 0.2-0.4 borderline- monitor, > 0.4 treat (assuming no pyuria etc.) and this is what our Boehringer rep advised as well, so I certainly wasn't being pushed into using medication unnecessarily.[/quote]

That's interesting - from what I remember of the information I was given at the Boehringer 'chronic care' roadshow was that even in the 0.2-0.4 borderline range, survival times were similar to the >0.5 range. Good to know that isn't being wildly extrapolated into a sales push though.

RE: Feline Urine Specific Gravity

Lucy Fleming — Thu, 26 Nov 2015 21:25:33 GMT

[quote user="Anthony Todd"]I think most are now saying that a low SG is, re ipso facto, cast iron, indisputable, absolute evidence confirming a diagnosis of kidney disease.[/quote]

no they aren't

RE: Feline Urine Specific Gravity

Anthony Todd — Thu, 26 Nov 2015 09:48:02 GMT

[quote user="Michael Woodhouse"]There is no such thing as a 'normal' USG without context.[/quote]

[big sigh] That was all I was, obviously ineptly, ever trying to get across!

RE: Feline Urine Specific Gravity

Michael Woodhouse — Thu, 26 Nov 2015 01:14:33 GMT

Former Member - urine specific gravity is a function of water intake and concentrating ability of the kidneys. I don't think anyone is grabbing cats off the street with a net and randomly testing only their urine and declaring them as having bad kidneys. We are discussing the workup of a cat that has azotaemia (although I agree there is a discussion point over the overlap of the IRIS range and the 'normal' given by the labs).

If the creatinine level in the blood increases then homeostatic mechanisms should come into play to lower that back to normal levels. The normal physiological response would be to produce more concentrated urine - the body is trying to shove as many waste products as it can into the bladder. If the waste products are building up in the bloodstream AND the urine is dilute then that is an inappropriate physiological response.

Whilst I accept that some cats will consume more water and produce more dilute urine, in the face of azotaemia that is physiologically inappropriate. I do also agree that cats that consume more water (through their food or otherwise) will produce more urine and may be able to maintain their blood creatinine level in the 'normal' range for longer than a cat that restricts its water intake and eats dry food.

There is no such thing as a 'normal' USG without context.

Does that explain?

RE: Feline Urine Specific Gravity

Anthony Todd — Wed, 25 Nov 2015 23:46:30 GMT

[quote user="Kate Richardson"]But that's the whole point Anthony, they will only take in more fluid than they metabolically need if they have an underlying medical reason to do so! [/quote]

So the well regarded and standard method of getting more water into a cat by making the wet food sloppy with water means the cat stops eating [and therefore taking in the extra water] because "they will only take in more fluid than they metabolically need if they have an underlying medical reason to do so!"?

A cat that loves milk or prawn juice will not drink any of it because "they will only take in more fluid than they metabolically need if they have an underlying medical reason to do so"?

[quote user="Kate Richardson"]Cats do not over drink for the sake of it[/quote]

That's just nonsense.

And, er, what about their love of propylene glycol? There's no metabolic or underlying reason there!!

Of course a cat with "an underlying medical reason to do so" will try and drink water from any source 'cos they need it, but that is not the same as a cat drinking propylene glycol 'cos they like the taste or prawn water or milk or slushy tinned cat food.

RE: Feline Urine Specific Gravity

Kate Richardson — Wed, 25 Nov 2015 21:35:05 GMT

[quote user="Anthony Todd"]Cats on wet food or water containing milk or cat's milk are taking in more water than they metabolically need and eliminate this by passing more dilute urine with a lower SG.[/quote]

But that's the whole point Anthony, they will only take in more fluid than they metabolically need if they have an underlying medical reason to do so! Or if their owners decide to syringe an extra 100mls of fluid into them daily!!! Cats do not over drink for the sake of it! Did you read my quote from the iCat care website from their page on the origins of cats?