feline chronic renal failure

Re: feline chronic renal failure

Rob Davis — Wed, 29 Dec 2010 12:28:58 GMT

Surely creatinine levels should be viewed no only against the laboratory's "normal" range and IRIS guidelines, but also in relation to the cat's body condition score. Creatinine of 190 would surely be more significant in a skinny cat vs a large muscular beast. In a perfect world it would be nice to have reference values from the individual before renal problems were diagnosed.

Re: feline chronic renal failure

Laurence Webb — Wed, 29 Dec 2010 11:12:41 GMT

I use the IRIS guidelines are intended for use in cats that have been diagnosed with CRF. If a cat's signalment fits it and it's got dilute urine in the absence of any other obvious cause (UTI, diabetes, big lumpy kidneys etc) then I use the IRIS guidelines. Ideally you'd demonstrate the persistence of suboptimal urine concentration as transient isothenuria can occur in normal animals.

If a cat's got well concentrated urine then it can't have CRF and you can accept higher urea/creat levels in those individuals than you would in a cat that is isothenuric. For those I use the lab reference figures although high normals should still be viewed with some suspicioun

Re: feline chronic renal failure

HMC — Wed, 29 Dec 2010 10:25:37 GMT

[quote user="Graham Bilbrough"]

It doesn't surprise me that different analysers have different reference intervals for creatinine (or other analytes). What does surprise me--and this is is NOT directly specifically at IRIS--is how frequently guidelines are issued without mention of the analyser used for the original study and how this might compare to the analysers commonly used in veterinary practice and at the UK reference laboratories. A pertinent example is for the Urine Protein to Urine Creatinine ratio (UPC). Here you will find a very different number when done 'in-house' or 'at the lab' and it really does emphasize the need for consistency when monitoring a trend.

[/quote]

Can we have a poll to see who uses the IRIS guidelines for creatinine and UPC cut-offs versus those published by the lab used?

I use IRIS and I would be interested to hear what other people use.

Re: feline chronic renal failure

Mark Holmes — Fri, 24 Dec 2010 13:37:33 GMT

Novartis advise that you can expect a 10mmhg reduction in systolic bp using fortekor whilst you can on occasion get more you cannot expect it. They suggest it is ok for borderline hypertension but not for true hypertension. (200+)

Re: feline chronic renal failure

Martin Atkinson — Fri, 24 Dec 2010 12:44:36 GMT

I have had experience on several occasions of benazepril causing profound systemic hypotension and have had to reduce dose or even stop, so it clearly can have a marked effect on BP. However in hypertensive cats (>200mmHg or showing occular symptoms) I would use amlodypine and would have no issue running it with ACEi if that was required for therapeutic purposes for either renal or cardiac disease but I would continue to closely monitor BP.

Re: feline chronic renal failure

Christopher Saul — Thu, 23 Dec 2010 22:39:03 GMT

I was thinking of mild/moderate hypertension when I wrote that post. It's true theat ACEi only lead to a moderate reduction in hypertension; nice point well made.

To be honest it depends on how hypertensive the patient is. If hypertension is severe ( more than about 200mmHg or so) or if there is any evidence of end-organ damage ( eg retinal vessel tortuosity) then I tend to go for amlodipine as my first line treatment. If SBP is elevated but less than this, and there is no evidence of end-organ damage, then I go for ACEi first. I use benazepril (fortekor), then re-test after about 3-4 weeks of treatment. If the ACEi alone fails to control the BP I'll add or change to amlodipine.

I think this approach is appropriate under the cascade as you have to justify using an unlisenced drug ( amlodipine)

Hope this helps

Chris

Re: feline chronic renal failure

Rob Davis — Thu, 23 Dec 2010 10:17:17 GMT

[quote user="Christopher Saul"]As for ACEi, in general terms I prescribe them if a patient has one or both of the following: 1) Proteinuria or borderline proteinuria ( I use the cut off value of 0.4 to define borderline proteinuric) 2) systemic hypertension[/quote]

I didn't think ACEi made a significant difference to systemic BP. I have always preferred to use amlodipine in hypertensive cats, or would you be using both?

Re: feline chronic renal failure

Christopher Saul — Wed, 22 Dec 2010 19:14:27 GMT

[quote user="Hannah Chilton"]Do you recommend the patient says on renal diet/ACEi?[/quote]

If I were sure that my patient had CKD, I would generally recommend a 'renal' diet - it is debatable whether a low phosphorous diet is necessary in normophospataemic patients, though 'renal' diets have benefits beyond just being low in phosphorous... they are high in omega 3 (which is known to be renoprotective), moderate in protein and high in soluble fibre ( thus increasing ammonia trapping within the GI tract) .

As for ACEi, in general terms I prescribe them if a patient has one or both of the following: 1) Proteinuria or borderline proteinuria ( I use the cut off value of 0.4 to define borderline proteinuric) 2) systemic hypertension

Hope this helps

Chris

Re: feline chronic renal failure

Laurence Webb — Wed, 22 Dec 2010 17:58:46 GMT

[quote user="Martin Atkinson"]I would give Fortekor at the ealiest signs of kidney disease in cats based solely on persistant azotaemia

[/quote]But the cat doesn't have persistent azotaemia. 197 a year ago and 111 now. That's a marginal temporary change.

[quote user="Martin Atkinson"]where other causes of this have been ruled out. [/quote] It doesn't appear that they have.

Re: feline chronic renal failure

HMC — Wed, 22 Dec 2010 17:54:22 GMT

[quote user="Graham Bilbrough"]It doesn't surprise me that different analysers have different reference intervals for creatinine (or other analytes). What does surprise me--and this is is NOT directly specifically at IRIS--is how frequently guidelines are issued without mention of the analyser used for the original study and how this might compare to the analysers commonly used in veterinary practice and at the UK reference laboratories. [/quote]

I agree, but I think the IRIS guidelines are very different from all other reference ranges that I have come across...

Re: feline chronic renal failure

Graham Bilbrough — Wed, 22 Dec 2010 17:32:39 GMT

Re: feline chronic renal failure

HMC — Wed, 22 Dec 2010 16:57:14 GMT

[quote user="Mark Holmes"]

1025 and 1030 is extrapolated from humans who only have the ability to concentrate to 1040,

In dogs who can concentrate to 1060, 1040 is considered a better indicator of a functionally adequate population of nephrons, USG levels of 1030-1040 in dehydrated or azotaemic dogs should raise suspicion of impairment of renal concentrating ability.

In cats who can concentrate to 1080+ values of 1045+ suggest urine concentrating capacity to proevent intrarenal azotaemia

[/quote]

So basically, not only have the creatinine reference ranges been updated with the IRIS guidelines but now the usg values I was taught at uni have been upgraded!

That is something that confuses me (bear of very little brain): why are the reference ranges for creatinine so different for any given analyser versus IRIS? For example: our in-house analyser has 190 as the upper limit for normal for creatinine but the IRIS grading system would count 190 as mildly azotaemic:

<140umol/l = grade 1/4 ie no azotaemia

140-249 = grade 2/4 ie mild azaotaemia

250-439 = grade 3/4 ie moderate azotaemia

>440 = grade 4/4 ie severe azotaemia

Re: feline chronic renal failure

Martin Atkinson — Wed, 22 Dec 2010 16:22:27 GMT

My views on this subject have are unequivocal and have been expressed (and criticised) on this forum previously. Benazepril has been shown to decrease glomerular damage by reducing intraglomerular blood pressue and renal protein loss. I would give Fortekor at the ealiest signs of kidney disease in cats based solely on persistant azotaemia where other causes of this have been ruled out. Rising creatinine and phosphate, reduced urine SG and raised UPC ratio just tell you the cat is in increasingly severe renal failure - why wait until then? Give the client the option. Unless they can't afford it or the cat won't take it - its a no-brainer for them, it will do no harm and will probably do a lot of good.

Re: feline chronic renal failure

Laurence Webb — Tue, 21 Dec 2010 19:21:47 GMT

Sarah Caney hedges her bets a bit more on the Renalzin website

72 1024x768 Normal 0

Normal cats produce concentrated urine with a USG usually greater than 1.035-1.040. A loss in renal concentrating ability is seen once two thirds or more of the functioning nephrons have been lost. Azotaemia with a USG <1.035-1.040 is usually considered evidence of primary renal disease.

So I would assume >1.045 is fine, <1.035 is dodgy if they've got azotaemia. Between is a grey area.

My understanding is that ACEi reduce GFR (efferent arteriole vasodilation reduces the hydrostatic pressure in the glomerular bvs) so you would often expect Fortekor etc to cause some increase in creatinine. The diet may be reducing the azotaemia although, as you point out, the initial diagnosis is a bit uncertain.

If the cat is well in itself then there is probably little harm in continuing the ACE-i but the benefits of it are uncertain. Rather than refute the entire diagnosis I'd probably advise the clients that the bloods look better so reasessment of the case is indicated. Aim to firm up the diagnosis with fuller biochem including BUN/creat/Phos/electrolytes plus full urinalysis including UPC, culture, sediment exam, check BP etc.

If they don't want to do all that then you could check UPC now and if non-proteinaemic stop the ACEi and recheck after 2-4 weeks (or just stop the ACEi, recheck UPC after 2-4 weeks then see if it may be worth restarting)

Re: feline chronic renal failure

Mark Holmes — Tue, 21 Dec 2010 17:32:26 GMT

[quote user="Hannah Chilton"]

I would have said that a usg of 1.036 is not submaximal but good concentrating ability? I use 1.030 and 1.025 as the cut-offs for cats and dogs respectively for well concentrated urine.

[/quote]

Danielle GM Uses 1045 as far as I am aware, and I have just checked my values,

1025 and 1030 is extrapolated from humans who only have the ability to concentrate to 1040,

In cats who can concentrate to 1080+ values of 1045+ suggest urine concentrating capacity to proevent intrarenal azotaemia

(Taken and paraphrased from Bayer: Urinalysis: A Clinical Guide to Compassionate Patient Care)

That would suggest azotaemia and USG of 1035 to be submaximal and suggestive of some but not complete renal insufficiency.

Re: feline chronic renal failure

Anonymous — Tue, 21 Dec 2010 17:26:57 GMT

Not wishing to add confusion to what I generally find a murky subject, but different people can mean different thngs when they report a urine SG as 1.036. Believe it or not, UK commercial labs operate on 2 different reporting scales but to my knowledge none of them tell you what 'scale' they are using! (Obviously most people do urine SG in-house, but if you are conned into buying a 'vet refractometer', then 1.036 to you will be different on most of the rest of the world's standard medical refractometers...)

Doesn't make a huge difference, but relevant if you're talking about 'cut-off points' (e.g. 1.035 or 1.040 or even 1.045 in a cat) for adequate concentration in presence of azotaemia.

Incidently, an inadequate urine SG (e.g. 1.020) in the presence of azotaemia in a polydipsic cat losing weight would also be entirely consistent with hyperthyroidism - I believe it can be very difficult to be totally sure you've diagnosed CKD in a GP setting without spending more money than a lot of clients wish to. Havng said that, think the potential benefits of ACEi are mild/moderate at best and not sure very good value for money (though better since 'Prilben' etc.). My general philosophy in the situation you describe is to continue to dispense the fortekor if that's all the client wants - i agree that you're stuck wth the dilemma of is it helping or was there a misdiagnosis in first place or just general variation in lab findings etc, but if stop it and cat becomes azotaemic and requires fluid therapy, you rsk being blamed! I generally am not a fan of any treatment which requires regular tabletting of cats, so if the owner-cat relationship is in anyway affected by the process, then I suggest that they could try stopping for a few weeks as "The kidnneys might be doing better..." and we could retest then if they wanted (BUN/Crea/Phos + simultaneous cystocentesis urine for SG, sediment check and UPC)...

Re: feline chronic renal failure

HMC — Tue, 21 Dec 2010 16:52:20 GMT

[quote user="Mark Holmes"]However as far as I am concerned then provided the cat has been azotaemic, with a submaximal urine concentration I would assume so. My understanding of SG is that you are not looking for isosthenuric urine but submaximal sg. [/quote]

I would have said that a usg of 1.036 is not submaximal but good concentrating ability? I use 1.030 and 1.025 as the cut-offs for cats and dogs respectively for well concentrated urine.

[quote user="Mark Holmes"]As far as soes this cat have renal disease, then I guess the age etc of the cat would help to tip the balance[/quote]

The cat is 12 years old (11 years at the time of the initial bt/ua).

Re: feline chronic renal failure

Rob Loxley — Tue, 21 Dec 2010 16:38:55 GMT

Urinalysis would be my next step.

Re: feline chronic renal failure

Mark Holmes — Tue, 21 Dec 2010 15:47:15 GMT

I think there are two aspects to this, firstly what benefit are ACEi in renal failure without an increase in UPCR. This has been covered many times and I am still not sure. I now usually present it to client with the arguments and let them decide what they would like to do.

As far as soes this cat have renal disease, then I guess the age etc of the cat would help to tip the balance. However as far as I am concerned then provided the cat has been azotaemic, with a submaximal urine concentration I would assume so. My understanding of SG is that you are not looking for isosthenuric urine but submaximal sg.

My assessment would be that as the kidneys can lose 65-70% function before showing symptoms of renal insufficiency, there will be a point at which they have some (but not full) concentrating function and at this point azotaemia may fluctuate around the upper end of normal. They might not have renal failure but will still be 60%ish reduced functional renal mass. If that were the state of my kidneys I would be worried. I would be more confident in making this diagnosis in 16yo cat than a 2yo and would request further investigations, ultrasound, urine cultures etc before being confident at the younger age and would suggest culture in the older cat as well.

Re: feline chronic renal failure

Richard Fox — Tue, 21 Dec 2010 15:30:40 GMT

I am no expert in U/C ratios but if you are unsure about the initial dx then re-review - I do it every week in my job.