T4: How low is too low?

Re: T4: How low is too low?

Anthony Todd — Sat, 10 Jan 2015 18:07:41 GMT

[quote user="John Dennis"]Hope this clears the matter[/quote]

Thanks, understand now; I'm a bit thick most of the time....

Re: T4: How low is too low?

Sammy82 — Sat, 10 Jan 2015 17:57:03 GMT

We should also keep in mind how the reference range is defined: 95% of all normal(healthy) animals will fall inside the range, which means that 5% have values outside the range without being abnormal or ill in any way, that's 1 in 20 healthy animals we test.

Re: T4: How low is too low?

John Dennis — Sat, 10 Jan 2015 17:43:30 GMT

[quote user="Anthony Todd"]Is this reply in the right thread??[/quote]

Sorry.

I really intended to be supportive about your statement on T4 variations in greyhounds and also the fact that normal values have become set in stone. I tried to indicate that clinical welfare is the priority not ensuring the "fit" to lab results.

Hope this clears the matter

Re: T4: How low is too low?

Anthony Todd — Sat, 10 Jan 2015 11:18:00 GMT

[quote user="John Dennis"]SNAP!!!!!. Patient welfare governs all, they can't always be made to live forever.[/quote]

Is this reply in the right thread??

Re: T4: How low is too low?

John Dennis — Sat, 10 Jan 2015 11:02:14 GMT

[quote user="Anthony Todd"]

Makes me smile when I remember the drubbing I got when I suggested that the "normal" T4 for a 7yo spayed greyhound might be different from the "normal" in a 2yo fit racer....

It seems that these days normal levels are set in stone!

[/quote]

SNAP!!!!!. Patient welfare governs all, they can't always be made to live forever.

Re: T4: How low is too low?

David Mills — Fri, 09 Jan 2015 19:47:47 GMT

T[quote user="Simon Neuhoff"]

Right found the article - Lucy Preece

"..ongoing hyperthyroidism has the potential to worsen CKD through activation of the RAAS system. Therefore, the idea that keeping T4 levels higher in patients with CKD in order to maintain GFR is outdated. In all patients - whether or not CKD is already present - it is important to tT4 levels in the lower half of the reference range."

ie NOT hypothyroid but lower half reference range.

[/quote] There is no evidence to support this opinion stated as fact.

Re: T4: How low is too low?

Simon Neuhoff — Fri, 09 Jan 2015 16:12:06 GMT

Right found the article - Lucy Preece

ie NOT hypothyroid but lower half reference range.

Re: T4: How low is too low?

Anthony Todd — Fri, 09 Jan 2015 15:43:03 GMT

[quote user="Martin Atkinson"]The problem being you don't know what is normal for this cat i.e. if it normally had a TT4 of near 50 then lower half may be too low.[/quote]

Makes me smile when I remember the drubbing I got when I suggested that the "normal" T4 for a 7yo spayed greyhound might be different from the "normal" in a 2yo fit racer....

It seems that these days normal levels are set in stone!

[quote user="Martin Atkinson"] importance of monitoring blood pressure in hyperthyroid and CKD cats.[/quote]

Having seen my 2 week old grandson having his blood pressure checked using the same instrument as adults but with a tiny inflatable cuff makes me hope the same would work in cats and dogs.

Re: T4: How low is too low?

Martin Atkinson — Fri, 09 Jan 2015 13:36:49 GMT

[quote user="Simon Neuhoff"]From what I have read more recently though this approach is now apparently outdated.[/quote]Well in that case it is outdated since the last seminar I went to by Mayank Seth from the Animal Health Trust in September but I'm happy to learn something new.

If nothing else it highlights that a common sense approach is indicated and that we should treat our patients not lab results.

Re: T4: How low is too low?

Richard Carter — Fri, 09 Jan 2015 11:38:08 GMT

thought the current feeling is to approach total control of hyperT4 with caution if it unmasks concurrent renal disease - ie better to be slightly hyper T4, eating, drinking, active etc to counter the anorexia of CRF

Re: T4: How low is too low?

Simon Neuhoff — Fri, 09 Jan 2015 10:19:38 GMT

[quote user="Martin Atkinson"]

[quote user="Simon Neuhoff"]As I understand it even in azotaemia you still want to control the hyperthyroidism - because it will contribute to ongoing renal damage (not to mention the other issues with poorly controlled hyperthyroidism). So you would aim for lower half of reference range, irrespective of azotaemia, [/quote]I would counter this although it does depend to some extent on the level of azotaemia. You are right that you need to control hyperthyroidism to prevent hypertension which could lead to further kidney damage but if it T4 goes too low then they may be hypotensive and cause under-perfusion. In mildly azotaemic cats I would go with what you say but in severe azotaemia I would aim for the upper half of normal range TT4. The problem being you don't know what is normal for this cat i.e. if it normally had a TT4 of near 50 then lower half may be too low.

I think if nothing else comes from this discussion it is the importance of monitoring blood pressure in hyperthyroid and CKD cats.

[/quote]

Shrug - that's what I used to do too. From what I have read more recently though this approach is now apparently outdated. Have looked for but can't find the damn article - will post it if I do.

Re: T4: How low is too low?

Martin Atkinson — Fri, 09 Jan 2015 10:06:57 GMT

I think if nothing else comes from this discussion it is the importance of monitoring blood pressure in hyperthyroid and CKD cats.

Re: T4: How low is too low?

Simon Neuhoff — Fri, 09 Jan 2015 09:55:40 GMT

As I understand it even in azotaemia you still want to control the hyperthyroidism - because it will contribute to ongoing renal damage (not to mention the other issues with poorly controlled hyperthyroidism). So you would aim for lower half of reference range, irrespective of azotaemia, but not so as to cause hypothyroidism. So I would be ok with the current doseage even if there was azotaemia.

Re: T4: How low is too low?

Kate Richardson — Thu, 08 Jan 2015 18:36:29 GMT

Agree with all the above, only thing I would add is don't just assess renal function with urea/creat, check urine SG as well, but I wouldn't change the dose in this cat if renal function is normal

Re: T4: How low is too low?

listhestar — Thu, 08 Jan 2015 16:32:33 GMT

[quote user="Hannah Wynne Richards"]What are his kidney parametrs like. If he's not obviously hypothyroid, then I'd use urea/creatinine to decide whether or not to slightly back off treatment.[/quote]

Would agree with the above. In a paper I read being hypothyroid didn't affect prognosis UNLESS azotaemic in which case then survival time was shortened (Williams et al, 2010)

Lisa

Reference

Williams, T. L., Elliott, J., & Syme, H. M. (2010). Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism. Journal of Veterinary Internal Medicine, 24(5), 1086-1092.

Re: T4: How low is too low?

Hannah Wynne Richards — Thu, 08 Jan 2015 15:40:39 GMT

What are his kidney parametrs like. If he's not obviously hypothyroid, then I'd use urea/creatinine to decide whether or not to slightly back off treatment.

Wynne

Re: T4: How low is too low?

james herriot lied — Thu, 08 Jan 2015 15:27:38 GMT

I've often wondered what the thyroid levels of some bilaterally-surgified cats would be - bet it'd be lower. I think you've got room to move, but thyroid meds tend to come in fairly discrete dosing regimes, so if the next step down causes increased clinical signs even with fairly normal T4, I'd be inclined to continue on your current dose.

Re: T4: How low is too low?

Martin Atkinson — Thu, 08 Jan 2015 15:27:19 GMT

Given that it is difficult to get it perfect I would not worry about chasing numbers, read what the cat is telling you. I aim to get T4 in the lower end of normal range and have only once had a cat show signs of hypothyroidism when it has been below normal and that had I131 therapy. Your 13.4 is in normal range so why worry and bet your bottom dollar next time you test it will be something different even if you leave the dose the same.

Other than the cat mentioned above, the only time it would concern me is if the cat is also azotaemic and I would aim for high end normal TT4 but sometimes you just have to live with what you can achieve in practical terms.