T4 and Free T4

[Raspberry]

I am wondering if anyone could help me with some feline blood test results. The Total T4 is under reference range (almost too low to give a number) and the Free T4 is well above reference range. The second score seems to be indicative of hyperthyroid, but why the low T4? There is also diabetes at play here.

If anyone can enlighten me, I would appreciate it. Thank-you.

[katsdar]

I found this for you hope it helps.
Feline Hyperthyroidism
Frequently Asked Questions, Information About Overactive Thyroid Conditions in Cats


by Mary Shomon

What is hyperthyroidism?

The thyroid is a butterfly shaped gland located on either side of a cat's windpipe. The thyroid produces hormones that regulate metabolism and organ function. With hyperthyroidism, the thyroid becomes overactive, and produces an excess of thyroid hormone.

How do cats get hyperthyroidism?

The main way cats develop hyperthyroidism is due to development of a benign tumor, known as an adenoma, in their thyroid gland. The tumor secretes excess thyroid hormone, creating the condition of hyperthyroidism.

How common is hyperthyroidism in cats?

Hyperthyroidism is one of the most common endocrine conditions affecting cats, in particular, older cats over the age of 10. The median age for acquiring hyperthyroidism is approximately 13 years of age, and very few cats develop the condition before the age of 10. Some veterinarians estimate that about 2% of cats over 10 will develop hyperthyroidism, and, due to factors that may include environmental exposures, that number is on the rise.

Is hyperthyroidism dangerous?

Untreated, hyperthyroidism in cats can lead to heart failure or kidney failure and can be fatal.

What are the symptoms of hyperthyroidism in cats?



Weight loss (typical, but not always)
Increased appetite without weight gain
Vomiting and diarrhea
Increased energy and friskiness
More vocalization
Demanding food more frequently
Drinking more water
More frequent urination
Decreased appetite (less common, but can be a symptom)
Decreased activity (less common, but can be a symptom)
Weakness (less common, but can be a symptom)
Labored breathing and panting (less common, but can be a symptom)
How is hyperthyroidism in cats diagnosed?

Primarily, diagnosis is made by blood test, measuring the level of thyroxine (T4) in the blood. High T4 levels are considered indicative of hyperthyroidism. Occasionally, if results are not conclusive, a more definitive -- and costly -- test known as Free T-4 may be run. And, some veterinarian will use other tests including T3 levels, T3 suppression test, thyrotropin-releasing hormone stimulation test, and thyroid radionuclide uptake and imaging ("thyroid scans"), to verify a hyperthyroidism diagnosis.

What are the treatment options for hyperthyroidism?

The three conventional treatment options are antithyroid drugs, surgical removal of the thyroid, and radioactive iodine treatment to disable the thyroid gland. Some practitioners also work with alternative therapies for milder forms of hyperthyroidism.

What is involved in antithyroid therapy?

Antithyroid therapy is the treatment of choice for many practitioners and cat owners, because it's non- invasive, and inexpensive. Antithyroid drug therapy involves putting the cat on the drug methimazole -- brand name Tapazole -- a human antithyroid drug. Downsides are that in some cats, it does not resolve the hyperthyroidism, and giving the cat a pill daily for life may be difficult. A small percentage of cats have some lethargy and vomiting as side effects. Typical cost of antithyroid drug therapy is $25 a month for life.

What is involved in surgery for hyperthyroidism?

Surgery -- known as thyroidectomy -- removes the affected part of the thyroid gland. Surgery can be an effective cure, and many veterinarians are capable of performing this surgery. Only a few days of hospitalization is required. Drawbacks, however, include the risk of anesthesia, particularly in an older cat, and the risk of removing the parathyroid glands, which can cause hypoparathyroidism. In some cases, there is also a risk of hypothyroidism if both lobes of the thyroid are removed. The typical cost of a thyroid surgery is approximately $900.

What is involved in radioactive iodine treatment for cats?

With radioactive iodine therapy, the cat receives a one-time injection of iodine I-131, which concentrates in the thyroid and irradiates and destroys the malfunctioning part of the gland. Healthy thyroid tissue is not damaged, and the risk of hypothyroidism is low. Almost all cat receiving radioactive iodine will return to normal thyroid function within a month or so of treatment. This procedure can be expensive, running approximately $1,200 on average.

Many veterinarians are not set up to do this sort of treatment, as it requires about a week's isolation for the cat while the radioactive material clears their system and the cat and their waste products are again safe for human exposure.

A national network, Radiocat, however, runs specialty radioactive iodine clinics for cats at 10 centers around the country, including: Phoenix, Ariz.; New Haven, Conn.; Wilmington, Del.; Marietta, Ga.; Wheeling, Ill.; Baltimore; White Plains, N.Y.; Pittsburgh, Pa.; Springfield, Va; and Waltham, Mass.

What alternative/complementary approaches may be pursued?

Some practitioners use alternative therapies for cats with mild hyperthyroidism. Because of the potential seriousness of hyperthyroidism, it's recommended that you work with a good holistic veterinarian or naturopath who specializes in pets to determine an effective treatment regimen for your cat.

Some of the alternative medicine approaches that have been effective include:
Traditional Chinese Medicine, including herbs and acupuncture
Bugleweed/Lycopus: This herb may, if used for several days sequentially, have an impact on mild hyperthyroidism
Lemon balm/Melissa officinalis: Can in some cases reduce the thyroid's output of thyroid hormone and alleviate mild hyperthyroidism.

[katsdar]

I found an 800 number for you to call and get more answers to your questions. Let me know how things turn out.
1-866-467-8228

What is Feline Hyperthyroidism?
Feline Hyperthyroidism is a disorder that occurs when the feline thyroid gland produces an excess of thyroid hormone. An excess of thyroid hormone affects all of the cat's organ systems.

Hyperthyroidism occurs in middle aged and senior cats. Both feline sexes and all breeds are equally at risk.

The thyroid gland is butterfly-shaped and is located in the neck region of the cat. Hyperthyroidism is caused by a tumor in this gland. Ninety eight percent of these tumors are benign (adenoma) and two percent are cancerous (carcinoma). Seventy percent of cats have both lobes affected.

Symptoms of Feline Hyperthyroidism may include:

weight loss
changes in behavior - anxiety or nervousness
excessive appetite or decreased appetite
increased water intake
hyperactivity or lethargy
excessive shedding, hair loss (alopecia), poor coat condition
diarrhea or vomiting
increased urination
cardiac symptoms - rapid heart rate, arrhythmia
Feline Hyperthyroidism is fatal if left untreated!

With Thyro-Cat, treatment for your cat's hyperthyroid condition is just a shot away.

[Raspberry]

Thank-you both for the information, I appreciate it. I will try the 1-800 number.

Does anybody know the significance of the blood test results? That is, the Total T4 is low and the Free T4 is high. What does this mean?

[growler~GateKeeper]

From Veterinary Partner
How to Tell if a Cat is Hyperthyroid

A blood panel is often ordered in the diagnostic work-up of any significant clinical signs. The blood panel surveys hepatic, renal, hematologic, and other body systems. Although there are multiple changes which fit hyperthyroidism, mild increases in liver enzymes are most commonly observed indicating mild (usually clinically insignificant) damage to the liver. The elevated T4 level forms the basis for diagnosis; there can be no other diagnosis in such a case.

If T4 is markedly elevated, the diagnosis is clear. Some cats have borderline results and require further testing.

When T4 Levels are Borderline

In older cats, the normal range for T4 is much lower than it is for young adult cats and thus sometimes it is not obvious whether a cat is truly hyperthyroid. Further, T4 levels are readily reduced by other disease states and there is some normal (but unpredictable) fluctuation in T4 throughout the day.

The easiest tests for your veterinarian to perform are called the T3 SUPPRESSION TEST and the EQUILIBRIUM DIALYSIS FREE T4. To do the T3 suppression test, the owner must be able to give the cat a pill three times a day for two days and return to the vet’s office for a blood test on the third day. In other words, some specific scheduling is necessary and the cat must be able to take pills.

The pill given is a T3 pill, active thyroid hormone. After two days of exposure to this medication, a normal thyroid will respond by reducing its T4 production. In a hyperthyroid cat, this negative feedback mechanism is not operating and the T4 level will not drop. Even borderline cases can be sorted out.

The Equilibrium Dialysis Free T4 represents a special form of thyroid hormone, the part that is not bound to blood proteins (as measured by a laboratory technique called equilibrium dialysis.) Unlike T3 and total T4 measurements, the Equilibrium Dialysis Free T4 is not as subject to the influence of non-thyroidal illness. For example, it is normal for total T4 levels to drop when one is sick; however, the free T4 portion remains unchanged. In this way, a hyperthyroid cat that is sick from another disease might have a T4 in the normal or borderline range but the Equilibrium Dialysis Free T4 would still be high enough to confirm the hyperthyroid condition. The Equilibrium Dialysis Free T4 is a simple blood test that can be run on any serum sample, though sometimes it must be sent to a special laboratory, thus requiring a few days for results.

Basically what your results mean is the T4 was too low to give a definative diagnosis it came back with a borderline Hyperthyroid diagnosis. Anytime you get a borderline diagnosis there should be a retest done to give a definate answer. The vet does another test to check the Free T4 which are T4 hormones not attached to the protein in the blood - this is done by testing the serum (blood has 3 parts red blood cells, white blood cells & serum also called platelets - this is the clear stuff that clots to stop blood flow in a wound). The diabetes is the reason your test result came back w/ T4 low & Free T4 high. If your cat did not have diabetes the T4 would have been high, as mentioned in the quote above the Free T4 is not affected by any other illness therefore it has shown the true T4 value.

The reason the T4 result was affected by the diabetes is the glucose/insulin levels in the blood protein are not at normal healthy (ie non diabetic) levels.

[Raspberry]

Thank-you very much for the information.

I did not know about the liver damage. Is it possible for the liver to regenerate once the hyperthyroid is treated?

[growler~GateKeeper]

Not all cats with HyperThyroidism have liver damage, only your vet can determine if your cat has liver damage concurant with the HyperT. My cat Duffy had HyperT but was treated with Radioactive Iodine Therapy - it is expensive & not available in all areas but it is actually a cure, she has been free of HyperT now for 2 years and no signs of liver damage. She does however have kidney failure but that's another story & not connected to the HyperThyroidism.

The regeneration of the liver will depend on the extend of damage & even with minimal damage it is unlikely the liver will regenerate 100%. However as mentioned in the following quote the liver will still function quite well when not functioning perfectly & even when 1/2 is removed - same as with humans.

from Pawprints and Purrs, Inc
A resilient organ, the liver has great powers to partially regenerate, and will continue to function even after over half of it has been removed. Managing the cat's diet will help the liver rest while it has a chance to heal. Many cases of hepatitis are acute, and only short-term management is needed. Long-term dietary are measures needed for a cat with chronic hepatitis. Dietary care for a cat with liver disease will include high quality protein. Cats with liver problems should not be given shellfish, organ meat, or foods containing fish meal. These contain purines which metabolize to form uric acid, something the cat's damaged liver cannot process.

[Raspberry]

Thanks very much for the information!

[pixi78]

My vet just called and gave me the results of the blood test, she said it wasn't the full results but that my cats thyroid level was 16 and that "normal" was 0.7 - 1. something. I'm worried this is very high. My vet makes housecalls and so our conversation today was brief and she'll be coming by early next week with the full results and medication to start treating her. I'm not sure what questions I should be asking or if I should be worried about how high her "number" is and if that means there might be other problems underlying. My cat is 11 and in the last year has lost about 15 lbs (she was extremely overweight, 25lbs at heaviest).
Anyway, if anyone has any helpful advice or facts I would very much appreciate it!

[growler~GateKeeper]

Hi pixi78 welcome to the board

Here are some threads that concern HyperT in cats, they may help you with some questions for your vet:
http://www.pets.ca/forum/showthread.php?t=60971

http://www.pets.ca/forum/showthread.php?t=52904

http://www.pets.ca/forum/showthread.php?t=64731

This is an excellent resource for information: Signs, Symptoms and Diagnosis of Hyperthyroidism

and this one too: http://felineoutreach.org/Education/...hyroidism.html

A US value of 16 is quite high, but your cat is young & getting treatment right away , is she displaying any unusual symptoms aside from the rapid weight loss?

As for if there are any underlying issues that will be dealt with once the thyroid value is stabilized, as that often will hide anything else.

What food is your cat currently eating?

[Dr Lee]

Originally Posted by growler

the Equilibrium Dialysis Free T4 is not as subject to the influence of non-thyroidal illness. For example, it is normal for total T4 levels to drop when one is sick; however, the free T4 portion remains unchanged. In this way, a hyperthyroid cat that is sick from another disease might have a T4 in the normal or borderline range but the Equilibrium Dialysis Free T4 would still be high enough to confirm the hyperthyroid condition.

The T4 (ED) was once thought to be the best thyroid test around. The above quote was a correct statement a few years ago and as such many cats that did not have thyroid disease were given a diagnosis of hyperthyroidism and placed on methimazole. This is not longer the current understanding.

For dogs, T4 (ED) is still a great test and I think important for almost every dog before a diagnosis of hypothryoidism is given. I have seen many profile that looked consistent with hypothyroidism until the T4(ED) was run. Dogs are very, very, very rare to get a functional hyperthyroid condition.

Many specialists feel that For cats, the T4 (ED) is an essentially worthless test. I have had this discussion with three different internal medicine specialists at Antech Diagnostics (if the test was remotely helpful, they would be recommending it as being part of the company. They are recommending never to run this test with cats). With that said, the T4 (ED) can help confirm hyperthyroid but it cannot diagnose hyperthryoidism when the resting T4 is low or normal at 2.5 or less.

So why is it being run in cats? The reason being.... several years ago, everyone was running this new thyroid supertest. So many of us were running it and coming in with the exact situation that is described here - normal T4, high T4 (ED) and clinical signs that may or may not be related. For a while many cats were erroneously being given hyperthyroid diagnoses and started on treatment (unfortunately this still happens). As time has gone by we realized that cat's T4 (ED) can go up for a variety of reasons and is no longer considered a great test for this. Illnesses and reasons unknown seem to account for what can be high or very high T4 (ED) in otherwise normal cats.

If a veterinarian runs a T4 and T4(ED) on a cat and you get a hyperthyroid diagnosis based on a high T4 (ED) when the resting T4 less than 2.5, they should consult with their free specialist consultation that is provided by the reference laboratories. (T4 can be run in house (poorly so at this time) but T3(ED) cannot). So if they have run a T4 (ED) then they can get a free internal medicine specialist consult which will verify what I have said in this post.

Of course just as I would have written this differently 5 years ago, things may change 5 years from now but as to the current understanding of feline thyroid function from the specialists - T4 is a good test, and T4(ED) is not..... in cats. For dogs, use both.

I hope that this clarifies and helps.

[Dr Lee]

Originally Posted by Raspberry

Is it possible for the liver to regenerate once the hyperthyroid is treated?

Yes. Often liver enzymes and function will return to normal.

[Dr Lee]

Originally Posted by pixi78

My cats thyroid level was 16 and... I'm worried this is very high. I'm not sure what questions I should be asking or if I should be worried about how high her "number" is and if that means there might be other problems underlying. My cat is 11 and in the last year has lost about 15 lbs

Many cats that have this high a thyroid can do well with treatment. The number is not as important as the pet's response to treatment. It will be important that her numbers get down and that her kidney values do not rise. Also monitoring liver, heart and blood pressure are important. I often switch hyperthyroid cats automatically to a kidney friendly diet (of course, each individual cat's status and requirements are a bit different).

Most cats are treated with methimazole which can come in a small tablet, flavored liquid or topical cream that is applied to the ears. There is a holistic option that has good data behind it but is not something I have experience with. There is also radioactive iodine therapy that can be curative - the cat is given radioactive iodine (I131) which goes virtually all to the thyroid gland, shrinks the gland back to normal and then is harmlessly eliminated. Surgery is occasionally still done but less common due to the success and safety of the radioactive iodine therapy. Most cats are treated with methimazole for life. I have referred many cats for I131 therapy who have been cured and require no additional medications. Not all cats are I131 candidates though.

Hope that helps.

[growler~GateKeeper]

Originally Posted by Dr Lee

The T4 (ED) was once thought to be the best thyroid test around. The above quote was a correct statement a few years ago and as such many cats that did not have thyroid disease were given a diagnosis of hyperthyroidism and placed on methimazole. This is not longer the current understanding.

My quoted post was from 2 years ago & that statement in it is still on the Veterinary Partner site. Thank you for the updated protocols surrounding these tests

[Dr Lee]

Originally Posted by growler

From the VETERINARY PARTNER SITE: the Equilibrium Dialysis Free T4 is not as subject to the influence of non-thyroidal illness. For example, it is normal for total T4 levels to drop when one is sick; however, the free T4 portion remains unchanged. In this way, a hyperthyroid cat that is sick from another disease might have a T4 in the normal or borderline range but the Equilibrium Dialysis Free T4 would still be high enough to confirm the hyperthyroid condition.

I have thought about this quote last night and re-read it because of the source. So let me clarify a bit.

I still disagree with the first part, free T4 (ED) is influenced by non-thyroidal causes as proved by the work of Dr Mark Peterson at UC Davis. For this reason, I still am not a fan of this overall quote by the Veterinary Partner site. It is also misleading by implying that a T4 (ED) is more accurate and can be read to diagnose in spite what the total T4 is.

On the last part of the quote, there is some truth here. If the total T4 is in a boarderline zone of 2.5 to 3.5-4, then the free T4 (ED) may be useful when there is also clinical signs to support a diagnosis. Some specialist will use the T4 (ED) at this point and some will recommend retesting in 1-2 months (the later being the option I usually go with as the diagnosis of hyperthyroid comes along with lifelong medication and monitoring).

So yes, T4 (ED) can help in a grey zone but it is not the gold standard test that it is in dogs.

Here is a quote from a specialist from the parent site of Veterinary Partner, "If the resting T4 is lower than 2.5 and the free T4 is elevated, it is likely to be due to non-thyroidal illness."

Hope that helps.

[little lark]

Has anyone had their cat tested for hyperthyroidism and had the T4 high (9) and the free T4 in the normal range? My cats only symptoms are some vomiting and loss of appetite. He is also showing moderate pancreatitis. He is 12 years old and completely healthy up until the last couple of months. He has lost a little less than a pound over the summer.

Thanks for any information.