T4 and TSH levels

RE: T4 and TSH levels

Anthony Todd — Tue, 17 May 2016 00:27:16 GMT

[quote user="Utlendigur"]

[quote user="Anthony Todd"]

[quote user="Utlendigur"]while on treatment and it was nearly 200. [/quote]

What happened in this particular case; could it have had hyperthyroidism, or triple dosed, for example?

[/quote]

No, T4 was slightly low before treatment (no other thyroid bloods done). Dog was hugely obese which increased suspicion of hypothyroidism. It was started on typical low-end starting dose (in answer to your previous question). Represented because of pupd, urinary incontinence, restlessness and panting. Symptoms resolved over several months after stopping treatment.

[/quote]

[sorry, on stupid ""notebook"]

What was the final dose rate and the final T4 level etc. because others on here say "therapeutic" dose rates in euthyroid animals cause no problems?

Seems odd that therapeutic rates caused such massive blood values even though the signs suggest "overdosing?

RE: T4 and TSH levels

Anthony Todd — Tue, 17 May 2016 00:19:54 GMT

sorry duplicate

RE: T4 and TSH levels

Utlendigur — Mon, 16 May 2016 16:10:11 GMT

[quote user="Anthony Todd"]

[quote user="Utlendigur"]while on treatment and it was nearly 200. [/quote]

What happened in this particular case; could it have had hyperthyroidism, or triple dosed, for example?

[/quote]

RE: T4 and TSH levels

Bob Russell — Mon, 16 May 2016 12:48:51 GMT

Leventa was unavailable for some time here so we had to move some patients to Thyforon. It is amazing how different the response was to liquid v's tablet. Absolutely not a straight swap!

The difficulty comes (and why I started the thread) when the dog 'looks' hypothyroid, has a low T4 but all confirmation tests come back WNL!

I don't consider this to be that common a diagnosis and medication should be started where there is clear evidence it is justified.

RE: T4 and TSH levels

Anthony Todd — Mon, 16 May 2016 06:26:54 GMT

[quote user="Utlendigur"]while on treatment and it was nearly 200. [/quote]

What happened in this particular case; could it have had hyperthyroidism, or triple dosed, for example?

RE: T4 and TSH levels

Aine Seavers — Sun, 15 May 2016 06:48:19 GMT

Vets on this forum perhaps don't prescribe it but sadly I see dogs who at 6mths of age (with no signs of cretinism-other than the diagnosis perhaps!) were put on thyroxine ! for years.

Re the gel tubes- if you always used them and you use the same lab then not such an issue but i do see differences in the gel activated and I am dealing with sighthounds of which about 11 breeds now have their own RI for these hormones so I need pin point accuracy. I also find out when the lab runs the tests as they bulk test them- and I take my samples the day before so in lab less than 24hrs when run not 6 days sitting there. There was a study that showed repeated freezing and thawing didnt harm the samples but I found some whacky results came back if the sample took too long sitting in lab to be processed so all my thyroids done on Tues mornings on fasted animals in plain serum tubes to be done within 24hrs.

I do see the thyrotoxicosis in the sighthound breeds- who on all the thyroid bloods and rhTSh ( I love that test) and the histo on gland when dead were true hypothyroid - yet could not be medicated into the normal therapeutic range without side effects and with only tiny doses- so for the breeds that perhaps have a phenotype that requires a low normal t4, trying to push them into a non breed specific post pill tt4 will cause distress. Equally I have seen mongrels with massive muscle wasting and tachycardia at the high end of normal that when took off the thyroxine were fine.

The non breed specific dose is 10-47ug/kg sid to bid- I rarely go above 10 bid in non sighthound breeds but the sighthounds go on 2.5-5ug/kg sid and very slowly over one month I walk them up in doses but rarely get beyond a total daily dose of 10ug either sid or divided bid.

In Uk you are lucky to have had a good vet version of levothyroxine because the bioavailability and bioequivalence of each formulation does vary. Here I have had to use oroxine to get the lower doses but the in the fridge then not in fridge then use in 2 weeks once open gives varying results-I tend to move the doses onto Mavlabs Thyroxine but its a 400 unit tablet. We did have sid levanta liquid for some months but MSD so busy with Bravecto the other meds not promoted so no market and its now gone.

So the dose you use, the formulation you use , the breed in which you use it that may have a genomic issue with the drug-all need to be factored in.

one of my vet heroes here- A 'House' doppelganger noted I phased all my thyroid cases (bar the neuro ones) onto the meds slowly to get a customised dose- he did not- when I explained that was how I was taught (cf say Mueller and Kirk 1989 edition for the cardiac concerns and phase in references that far back) he said his 'Jedi Master"had taught him to whack it in fast- but as there was more than one Jedi Master- he could accept my logic even if he didnt always do it- so keep doing what you do and if you get a tricky case then maybe some of the above might help explain the outlier behaviour.

RE: T4 and TSH levels

Michael Woodhouse — Sun, 15 May 2016 01:12:01 GMT

Aine - I don't think any of us are advocating routine screening and treatment of asymptomatic dogs solely based on a single T4.

The dogs discussed here are those with supportive clinical signs (and usually a low T4). remembering that diagnostic sensitivity increases with a test when used to confirm suspected disease compared to when used to screen an undifferentiated population (prevalence).

I'm also interested in your comments regarding serum gel tubes - we use them exclusively and get many normal T4 results back. I wonder whether this is kit or methodology specific?

My final thought - do you think you see this iatrogenic thyrotoxicosis in animals with peak blood T4 levels in the normal range? We would always check after starting Tx and then periodically.

RE: T4 and TSH levels

Anthony Todd — Sun, 15 May 2016 01:01:53 GMT

[quote user="Aine Seavers"]drug induced thyrotoxicosis[/quote]

What sort of dose rates were being given though?

Not disputing posts but we have had threads on this subject which weren't as they seemed.....

My Google turns up loads of "massive overdoses", and lurid titles, a lot involving iodine supplement, even suicide attempts but none [as far as I can find] of a therapeutic dose range causing adverse signs in an euthyroid patient.

RE: T4 and TSH levels

Aine Seavers — Sun, 15 May 2016 00:47:47 GMT

yes, it was those exact cases that got me hooked into researching this issue-the dog losing muscle mass as well as weight, with weakness and head bobbing-put down to neoplasia when it was drug induced thyrotoxicosis-and the milder cases with lower end tachycardia at yearly check up-owners thought dogs had periods of being 'sad' or uncomfortable- which an arhythmia or tachy would do. Often the drug was prescribed not because of any clinical signs(the only reason you should ever do a tt4) but because the in house lab had a tt4 kit run with every sample-with no attention given tothe age or gender or it being on a fed sample of a sighthound or thin dog on a hot day of an afternoon run on a gel activated tube with meds or vaccination in previous month or some natural supplements esp those with celery extract in them and surprise surprise there was a low tt4-

RE: T4 and TSH levels

Utlendigur — Sat, 14 May 2016 20:09:00 GMT

[quote user="Michael Woodhouse"]I worked in a practice that used to do as Anthony says start dogs on thyroxin with a single low T4 and there were a number of patients put on T4 because they 'looked' hypo and no testing was done. I never knew of one coming to any harm.[/quote]

Maybe you were just lucky. I worked in a similar practice and saw a couple of dogs come back after a few weeks because they started panting all the time, were unsettled, tachycardic, pupd etc. One of them I can remember we rechecked the T4 while on treatment and it was nearly 200. I can't believe that there wasn't some degree of harm due to hypertension, cardiac effects etc

RE: T4 and TSH levels

Aine Seavers — Sat, 14 May 2016 12:55:12 GMT

[quote user="Michael Woodhouse"] was asked by a student if T4 we suppressed by non thyroidal illness would the animal still benefit from some thryroxine supplementation in the mean time - even if not clinically hypothyroid. I didn't have the answer - but it doesn't sound daft.[/quote]

. In cases of illness and malnutrition, the body expresses “low T3 syndrome”wherein the production of the most potent thyroid hormone, (T3), is down regulated by suppression of the enzyme necessary to convert T4 to T3. This reduced production is perceived to be a beneficial adaptive mechanism, whereby the body acts to limit protein loss by attempting to decrease the metabolic rate during chronic or severe illness. Putting the MR rate back up in such a stressed patient is yet to be proven to be beneficial and may well be harmful.

An age related scenariohas been reported in 2011 in the human field, where concerns have been raised about higher doses of levo-thyroxine creating an increased risk of bone fracture and atrial fibrillation, especially in the elderly patient. A dose-response relationship was documented, with the evidence provided that the requirements for thyroxine decrease with age, to perhaps only one-half to one-third the requirements of younger and middle aged adults

The short half-life of T4, 12-24 hours d in the dog makes over-supplementation theoretically more difficult in comparison to people but as we know more about genetic adversomics and genetic prescribing we are beginning to document individuals and breeds who have drug issues- look at ivermectins in herding breeds- that sort of scenario.

The situation is confusing, as long as we accept this is not a straight forward condition to diagnose, test and treat then animals will be a lot safer, a lot less drugs dispensed and more targeted treatments will prevail. I have taken so many young dogs off thyroxine and years later no issue for them.

RE: T4 and TSH levels

Aine Seavers — Sat, 14 May 2016 12:41:35 GMT

there are thryoxine responsive conditions that are not hypothyoidism, thyroxine has many effects so response to it per se not a diagnose of hypothyroidism. Equally, the drug is not as safe as we were told, in the elderly it can cause cardiac concerns, in humans there are now serious drug related dose related side effects in one third of elderly patients, vets who deal with sighthound breeds often report dogs unable to tolerate standard doses without some distressing side effects so we are concerned about genetic adversomics to this drug re over and under metabolisers of the drug plus in an ill animal low thyroid can be a protective state and pushing the levels back up and the MR puts an ill catabolic patient into a high demand state. If I do a thyroxine trial I phase in slowly to titrate to the most accurate dose possible watching for side effects (except if its a neuro case I am worried about myxodema comas-the black labrador presentation, then it's fast in) and I always do a post pill TT4 at peak and sometimes trough 1-3months later depending on my patients and initial signs and ongoing tolerance. I got into thyroid research because of the over testing , over diagnosis and over treatment of this condition and found my concerns to be true so I test less overall in dogs , but test the suspected or diagnosed individual dog more often-it is the TREND of the values-not the one off value on one day in one moment of a pet's life that is important

RE: T4 and TSH levels

Michael Woodhouse — Sat, 14 May 2016 12:37:52 GMT

I was asked by a student if T4 we suppressed by non thyroidal illness would the animal still benefit from some thryroxin supplementation in the mean time - even if not clinically hypothyroid. I didn't have the answer - but it doesn't sound daft.

I worked in a practice that used to do as Anthony says start dogs on thyroxin with a single low T4 and there were a number of patients put on T4 because they 'looked' hypo and no testing was done. I never knew of one coming to any harm.

We also have dogs in the practice that look hypothyroid, have had a low T4, normal TSH and we've messed on doing lots of testing, repeat bloods, free T4 etc - in the end they almost all end up on medication - you just spend a lot of money getting there, and create a lot of owner (and dare I say it vet) frustration. Given an owner with limited funds, a dog with supportive clinical signs and a low T4 I don't believe a therapeutic trial is necessarily bad medicine - we'd offer everything as per the textbook.

I don't know what is for the best. I realise that Aine is just trying to help, but it clouds things even further!

RE: T4 and TSH levels

Anthony Todd — Sat, 14 May 2016 08:14:57 GMT

This harks back to bald greyhound thighs and the drubbing I got when I suggested a trial in some of these greyhounds.

Why doesn't anyone just suggest a trial of thyroxin instead of chasing blood values all the time?

It's very safe and probably cheaper and definitely more diagnostic than questionable blood values.

RE: T4 and TSH levels

Aine Seavers — Sat, 14 May 2016 07:27:01 GMT

Forgot to say-for me bradycardia is one of the big red lights I might have hypot4 when derm lesions also present, that and collar band friction more than anything else (even rat's tail) will make me suspicious. Also see if you can take the thyroid in plain non gel activated serum tubes.

RE: T4 and TSH levels

Aine Seavers — Sat, 14 May 2016 07:23:16 GMT

intra and inter test variation is huge. Only test in presence of clinical signs. Know your BREED Specific RI values. Adjust for breed, age and wt of dog. Adjust if not fasted or test done after noon or on a very hot day. Know that fat animals have HIGHER TT4 so a fat animal with a normal to high tt4 is probably not hypothyroid. There is a seesaw effect where as one goes down, other goes up-so you may be still on the 160-200 angle line and so retest in 2months and check the TREND as to what your values are doing. I also find that if you put an obese animal on Hills Rd and it doesn't lose wt- the 2 I have had in 30 years where hypothyroid but thankfully no atherosclerosis risk as was on the rd during that time. If you have a run of cases then something is up-either you have a genetic familial line which is causing an issue -so check pedigrees or you have poor nutrition and see some clinical signs imitating hypot4. Hypothyroid can be the great imitator but other conditions can mimic it back. I have done 1000s of thyroid blood tests now in last 10years as part of my research and I am totally ocd about when i test, how I test, where I send my tests to (same lab each time) and how I then interpret my results. But in a general practice setting-I rarely do a thyroid test in a month-the test is overused in my opinion and then misread.

RE: T4 and TSH levels

Rob Davis — Thu, 12 May 2016 17:17:49 GMT

I'm probably being dim, but ..... how are the cases being diagnosed as hypothyroid if TSH is normal? Is it purely on response to clinical signs?

RE: T4 and TSH levels

Linda Filshie — Wed, 11 May 2016 21:29:05 GMT

Ah, found it! Or at least one piece of research which references this:

TL/DR: Tiny study: 54 dogs with hypothyroidism, 76% had high TSH.

RE: T4 and TSH levels

Linda Filshie — Wed, 11 May 2016 21:05:38 GMT

I've got a cracking current case: symmetrical alopecia, rat tail, is a chubster, chol through the roof (>18mmol/l!!!) T4 7, FT4 <3.9, no sign of non thyroidal illness but TSH is low normal. Meh, I don't know where the 20% figure comes from, I must see if I can hunt up the study. I know that there's pressure from human hypothyroid patients to get doctors to move away from just testing TSH to screen for thyroid disease/thyroid monitoring.

Edit:Merck says 20-40% - no reference though. Clinician's Brief:33%, also no reference. Michigan State University 15%. Will keep looking but I'm beginning to feel like this is one of those figures that is plucked out of the air because "it sounds reasonable."

RE: T4 and TSH levels

Bob Russell — Wed, 11 May 2016 16:43:42 GMT

[quote user="Richard Carter"]

think you need to have at least some of the clinical signs of obesity, poor coat, lethargy, raised cholesterol alongside the low TT4 if the TSH is normal. Does TT4 have a diurnal or seasonal rhythm??

[/quote]

Got the lethargy, poor coat and cholesterol a hairs breath below the maximum normal range!

If it walks like a duck ....... (until you check the TSH levels!)

RE: T4 and TSH levels

Richard Carter — Wed, 11 May 2016 16:32:30 GMT

think you need to have at least some of the clinical signs of obesity, poor coat, lethargy, raised cholesterol alongside the low TT4 if the TSH is normal. Does TT4 have a diurnal or seasonal rhythm??

RE: T4 and TSH levels

KMurphy — Wed, 11 May 2016 10:50:33 GMT

You could check for thyroid antibodies as an additional test or retest in 6-8 weeks and chances are things would have fallen more into line with diagnostic criteria.

When you say free T4 is equivocal, what levels are you getting? If you have free T4 hovering somewhere near the low end of normal and a dog showing all the signs of being hypothyroid then there is probably enough clinical suspicion to justify a therapeutic trial.

Being hypothyroid myself, I really feel for these dogs - it's not life-threatening but it's definitely not fun!