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I'd still suggest trying him on tapazole for a while ... obtain the tapazole in compounded form to avoid giving pills.

He will be having an Feline Early Renal Detection test just before he goes in as I know blood tests are not that indicative. This is a new procedure and is very accurate.

I read your other posts and I don't think the ERD is as accurate or reliable as you seem to think it is. We've used it.. The ERD is a screening test - not a definitive renal function test... - It detects nephron damage - it doesn't measure actual renal function.. nor can it predict renal function after I-131 tx. Also, the results can be affected by a slew of conditions other than CRF. I wouldn't make any irreversible decisions based on the results of the test.
The smart play would be treating your cat with methimazole for a month or two and closely monitoring kidney function (BUN/Cr) while on the medication. If his kidney function remains stable when he reaches euthyroidism - then I-131 may be an option -although I wouldn't opt for I-131tx for a 14 y/o cat... If azotemia develops or worsens when he reaches euthyroidism you can adjust the dosage until you strike a balance between an "acceptable" level of hyperthyroidism and an "acceptable" level of azotemia... You don't have this safety and flexibility with any other txs.
Think about it.
Good luck.
Phil
I read your other posts and I don't think the ERD is as accurate or reliable as you seem to ... slew of conditions other than CRF. I wouldn't make any irreversible decisions based on the results of the test.

Hmmnn, I was getting the impression it was the holy grail of testing.
The smart play would be treating your cat with methimazole for a month or two and closely monitoring kidney function ... and an "acceptable" level of azotemia... You don't have this safety and flexibility with any other txs. Think about it.

I've heard enough so far of the above advice that I'm going to reopen discussions with my vet and the specialists. I will post the summary of my discussions as soon as I can reach them on Monday.

Thanks Phil and everyone else who also expressed the same concerns.

-mhd
I'd still suggest trying him on tapazole for a while ... obtain the tapazole in compounded form to avoid giving pills.

He will be having an Feline Early Renal Detection test just before he goes in as I know blood tests are not that indicative. This is a new procedure and is very accurate.

It's promising for detecting early CRF in itself, but it's not overly specific, so I would not rely on it for making a decision regarding the use of I-131. You might want to consider the iohexol clearance test which was mentioned in the link I sent you, but I don't know if you can get that run in Canada.
HTH
Helen
It's promising for detecting early CRF in itself, but it's not overly specific, so I would not rely on it ... was mentioned in the link I sent you, but I don't know if you can get that run in Canada.

I am now going to reexamine the I-131 treatment we had decided on. As I explained in a recent previous post I am now going to discuss all possibilities of CRF with my vet and the clinic (www.tvvs.ca).

I am especially interested in this iohexol treatment mentioned in your link and it's availability in Canada. Hopefully the clinic can perform this procedure since the facility is part of the Lawson Health Research Institute. As the research arm of the London Health Sciences Centre, the LHRI is one of Canada's three largest hospital-based research institutes.
I am a little confused about the CRF issue however. If the thyroid condition is masking an underlying CRF condition, is the implication that the CRF will get worse or just will expose itself.

Does it have to get worse to expose itself, or will a thyroid procedure unmask a condition at its current numbers?

Thanks
-Maurice
It's promising for detecting early CRF in itself, but it's ... I don't know if you can get thatrun in Canada.

I am now going to reexamine the I-131 treatment we had decided on. As I explained in a recent previous ... the clinic (www.tvvs.ca). I am especially interested in this iohexol treatment mentioned in your link and it's availability in Canada.

There's a much better and much more accurate renal function test than iohexol. The nuclear med facility that offers the I-131 tx probably also offers planar renal scintigraphy (a/k/a quantitative renal scintigraphy) because PRS uses the same principal and equipment as I-131tx.

PRS is so much better than iohexol because you can quickly and noninvasively* measure total and *individual* kidney function (GRF) in *awake cats! The procedure takes about 10 minutes and doesn't require overnight hospitalization.
Hopefully the clinic can perform
this procedure since the facility is part of the Lawson Health Research Institute. As the research arm of the London Health Sciences Centre, the LHRI is one of Canada's three largest hospital-based research institutes.

Sounds like a top-shelf facility - I'd be very surprized if they didn't offer PRS.
I am a little confused about the CRF issue however. If the thyroid condition is masking an underlying CRF condition, ... it have to get worse to expose itself, or will a thyroid procedure unmask a condition at its current numbers?

Hyperthyroidism masks true renal function because it falsely elevates GFR by increasing both, the heart's output and renal blood flow the volume of blood flowing through the kidneys to be filtered. This gives the impression that the kidneys are filtering more blood than they actually are instead of at just higher rate. Kinda like a clogged oil filter that cleans more oil only because the engine is revving faster.
After hyperthyroidism is treated, cardiac output, renal blood flow and true GRF slow down to their normal rates which will unmask CRF in cats with underlying disease. If the cat doesn't have underlying CRF, GRF will not slow down enough to cause develoment of overt renal failure.

IOW, treatment doesn't cause or worsen CRF, it simply unmasks the true GRF.

HTH,
Phil
There's a much better and much more accurate renal function test than iohexol. The nuclear med facility that offers the ... and doesn't require overnight hospitalization. Sounds like a top-shelf facility - I'd be very surprized if they didn't offer PRS.

They do Gamma Scintigraphy but no mention of the planar renal test. Here is a link to the Scintigraphy service at the clinic

http://www.tvvs.ca/scintigraphy frameset.htm
I will ask therm tomorrow.
Thanks for the info.
-mhd
There's a much better and much more accurate renal function ... - I'd be very surprized if they didn't offer PRS.

They do Gamma Scintigraphy but no mention of the planar renal test. Here is a link to the Scintigraphy service at the clinic http://www.tvvs.ca/scintigraphy frameset.htm I will ask therm tomorrow. Thanks for the info. -mhd

As good as PRS is it still won't give you an accurrate assessment or prediction of renal functon after tx if you run the test while the cat is still hyperthyroid. PRS and iohexol both depend GRF to determine renal runction - Hyperthyroidism falsely elevates GRF - so the results you get won't be accurate.
Without invasive tests, the only way you'll know if his GFR will slow down enough after tx to unmask CRF is to measure his renal function when he reaches euthyroidism while taking Tapazole... This is what his true renal function should be after treatment when his T4 levels are normal.

Btw, the most accurate T4 test is fT4ED.
Good luck.
Phil
IOW, treatment doesn't cause or worsen CRF, it simply unmasks the true GRF.

So aren't we basically facing CRF anyway and shouldn't be avoiding getting his thyroid to function properly? Or is elevated GRF from hyperthyroidism tolerated to a certain extent as a lessor of 2 evils?

He does need dental work that has been delayed because of the hyperthyroidism and I don't really see any option but to get him to reach euthyroidism through treatment.
I just got back an email from TVVS with the following information...

"One more test that can be run at your home clinic is to run a creatinine test, this is also a kidney enzyme that can give us an idea of how the kidneys are functioning.
The other thing that I would consider is to give a low dose injection of 131-I to gradually bring the T4 down (this would mean that cat could go home the same day). We do this method with cats that we know are at risk with their kidneys and so far this has been an excellent way of treating them.
The only disadvantage is that we would need to repeat the bloodwork in
12 weeks and give another low dose injection. It is even possiblethat your cat may need a third injection."
Any comments on the above Phil?
-mhd
IOW, treatment doesn't cause or worsen CRF, it simply unmasks the trueGRF.

So aren't we basically facing CRF anyway and shouldn't be avoiding getting his thyroid to function properly?

Absolutely! Thyrotoxicosis affects virtually every organ system in the body - especially the cardiovascular system and the skin - can cause retinal detachment secondary to hypertension and myocardial hypertrophy (thyrotoxic heart disease) similar to hyperthrophic cardiomyopathy.
Or is elevated GRF from
hyperthyroidism tolerated to a certain extent as a lessor of 2 evils?

Elevated GRF isn't a problem in itself because it augments renal function. The causes of elevated GRF are the problems.
Cats with severe or end-stage CRF would probably benefit more by not treating the thyrotoxicosis because it augments GFR unless the clinical signs of thyrotoxicosis were so severe or unmanageable like if the cat develops congestive heart failure secondary to thyrotoxic heart disease, there'd probably be no choice but to treat the hyperthyroidism. In this case, an antithyroid drug would be the treatment of choice because the dosage can be adjusted accordingly - up or down. The cat could be left mildly ("acceptably") hyperthyroid and/or mildly (acceptably") azotemic - so neither parameter is in the critical area.
He does need dental work that has been delayed because of the hyperthyroidism and I don't really see any option ... creatinine test, this is also a kidney enzyme that can give us an idea of how the kidneys are functioning.

No no no... Creatinine clearence test also relies on GFR to determine renal function. Thyrotoxicosis falsely elevates GRF so the results won't refect the true renal function. The only way any GRF test will yeild an accurate result is when the GRF isn't affected by thyrotoxicosis or any other illness or condition.
The other thing that I would consider is to give a low dose injection of 131-I to gradually bring the ... dose injection. It is even possible that your cat may need a third injection." Any comments on the above Phil?

Three treatments? That's absurd. They're just trying to push the I-131 tx. You can eliminate all this trouble and triple expense and stress for the cat by simply beginning Tapazole tx at an initial low dose and gradually increasing the dose by 2.5 mg every 2 weeks until his T4 is in the normal range and see where his BUN/Cr are. Its a very simple process...

Phil
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