Thyroid Tests

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Allie
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Thyroid Tests

Postby Allie » Tue Feb 03, 2009 1:55 pm

I am planning to have Sidney Bean's thyroid checked on the 17th. I just need to know what to expect and what I should be asking, etc.
Is this just a blood test?
We've never had the thyroid done, but after doing allergy/yeast research, it seems like something I should have done a while ago.

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Maryellen
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Postby Maryellen » Tue Feb 03, 2009 2:16 pm

yep its just a blood test.. the vet will probably send it out to MSU as that is close to you to get the results..

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Postby Allie » Tue Feb 03, 2009 2:59 pm

He has the ability to do it in house, and I will have results right away, is what the tech told me over them phone.

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Postby Maryellen » Tue Feb 03, 2009 3:35 pm

as long as they are accurate.. can he do all the proper thyroid tests? sometimes its better to be safe then sorry and do all the tests for the thryoid..

Total Thyroxine TT4
Total Triiodothyronine TT3
Free T4
Free Triiodothyronine FT3
T4 Autoantibody
T3 Autoantibody
Thyroid Stimulating hormone
Thyroglobulin autoantibody

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Allie
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Postby Allie » Tue Feb 03, 2009 3:48 pm

Yes, I will print this and bring it with me. He may be able to do some in house and send some out.
Do you have a link where I can read about all of these levels and what they mean/why I am checking them? I want to understand it first. :)

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Postby Maryellen » Tue Feb 03, 2009 3:58 pm

no, i just wrote down everything the holistic vet had tested for rubys thryoid at MSU lol.. i figured with all that he tested her for the chances of her thryoid being messed up were pretty slim. maybe try googling it?

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Postby Allie » Tue Feb 03, 2009 5:56 pm

Thanks!
Maybe someone else here will have input too. :))

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Postby pblove » Tue Feb 03, 2009 6:22 pm

The most commonly used thyroid tests are those that evaluate thyroid gland function by measuring thyroid hormone concentrations in the blood. The Total T4, Total T3, Free T4 and TSH concentration tests measure various hormone concentrations at rest. The TSH and TRH stimulation tests measure hormone concentrations after stimulation of the thyroid gland. Other available tests evaluate thyroid gland pathology and include the measurement of antibodies to thyroid hormones (T3 or T4) or thyroglobulin, as well as thyroid biopsy.

A much less common diagnostic procedure is the Radioactive Iodine Uptake (RAIU) study. RAIU studies do not accurately reflect thyroid gland function but simply determine the turnover of iodine in the thyroid gland. Results can be affected by the amount of iodide in the diet and non-thyroid illness. Because of these factors, as well as the expense, radiation exposure and the necessity for sedation, RAIU studies and radioisotope scans are not routinely used to diagnose hypothyroidism in dogs.

Hormone concentrations are usually measured by radioimmunoassay (RIA), although chemiluminescence, fluorescence polarization (TDX) and enzyme-linked immunosorbent (ELISA) assays are also being used. Regardless of the assay, it is important that the laboratory uses an assay that has been validated for use in dogs and that each laboratory establishes its own normal canine reference ranges. While most veterinary laboratories have done this, it is less common in human reference laboratories. It is essential to verify this when ordering tests from a human laboratory.

TOTAL T3 CONCENTRATION
Total T3 concentration (TT3) is the amount of total (free plus protein-bound) tri-iodothyronine (liothyronine) measured in the blood. It is the most active form of thyroid hormone at the cellular level. However, it is not the major hormone made by the thyroid gland and is formed by conversion from T4 (or thyroxine) in the peripheral tissues of the body. Hypothyroid dogs will often have normal concentrations of TT3 in the blood. Some veterinarians propose that there can be a defect in the conversion of T4 to T3, thus causing hypothyroidism. This defect is rare in people and not well documented in dogs. Occasionally, hypothyroid dogs form antibodies to circulating T3 in the blood, due to immune-mediated disease. These dogs can show elevated concentrations of TT3 in the blood. Because of these facts, measurement of TT3 in the blood is not an accurate reflection of thyroid gland function.

TOTAL T4 CONCENTRATION
Total T4 concentration (TT4) is the amount of total (free plus protein-bound) thyroxine measured in the blood. It is the predominant hormone made by the thyroid gland. While it has some biological activity itself, its major purpose is to be converted to T3, the more active thyroid hormone, in the peripheral tissues of the body. The free portion of T4 is the active available form of the hormone, while the protein-bound portion serves as a reservoir for hormone in the circulating blood. The protein-bound portion of TT4 can be lowered by non-thyroid illnesses, other hormones (cortisol) and certain drugs. Drugs that can lower protein-bound T4 (and therefore TT4) include steroids (cortisone, prednisolone, prednisone, etc.), non-steroidal anti-inflammatory drugs (phenylbutazone and others), anticonvulsant or seizure drugs (phenobarbital), certain potentiated sulfa drug antibiotics and potentially other drugs. Therefore, a dog with normal thyroid gland function could have a low TT4 due to lowering the protein-bound portion of TT4. It is very important that the veterinarian evaluating a dog for thyroid function know about all medications and any other medical conditions that the dog might be suffering from. Results of the measurement of TT4 can be misleading if one of the above mentioned conditions exist.

FREE T4 CONCENTRATION
Free T4 concentration is the amount of free or active thyroxine not bound to protein in the blood. As previously explained, protein-bound T4 can be lowered by non-thyroid illness and drugs. The free T4 portion is less likely to be affected by non-thyroid illness and drugs; therefore, it more accurately reflects true thyroid gland function. However, steroids (or a condition of excess internal cortisol called Cushing's Syndrome) can lower free T4 concentrations in some cases.

When measuring free T4 concentrations, it is important that the laboratory utilize a technique called equilibrium dialysis in performing the free T4 assay. Other "analog" techniques are not as useful in obtaining accurate results. Due to this equilibrium dialysis step which properly separates the free T4, this test is more expensive than other hormone assays. A formula incorporating the concentration of free T4 measured by equilibrium dialysis and cholesterol may be utilized to improve the diagnostic accuracy of a single blood sample.

TSH STIMULATION TEST
The current "gold standard" test for measuring thyroid gland function is called the TSH stimulation test. In this test, T4 concentrations in the blood are measured before and 6 hours after the administration of TSH (thyroid stimulating hormone or thyrotropin). TSH is the hormone normally produced by the pituitary gland which stimulates the thyroid gland to produce hormone. If the T4 concentration in the blood sample taken 6 hours after giving the TSH is not significantly greater than that in the blood sample taken before the TSH is given, then this means that the thyroid gland is not able to produce adequate thyroid hormone (primary hypothyroidism). Unfortunately, the utility of this test is limited by the availability and cost of TSH. The veterinary TSH product is currently not available and the human TSH product is difficult to find. Costs of TSH range from $160.00 to $220.00 for 10 units of TSH (1-5 units needed per test).

TRH STIMULATION TEST
The TRH (thyrotropin releasing hormone stimulation test) is another test for measuring T4 before and after thyroid gland stimulation. TRH is produced by the hypothalamus to stimulate the pituitary gland to produce TSH which in turn stimulates the thyroid gland to produce T4. The TRH stimulation test is not as good a test as the TSH stimulation test because the amount of increase in T4 after administration is not as great in normal dogs as with TSH, so it makes it harder to distinguish normal from subnormal response. Also side effects (salivation, vomiting, diarrhea, panting and rapid heart rate) are frequent when TRH is given. The cost of TRH is not as great as TSH but it is also difficult to find.

TSH CONCENTRATION
The direct measurement of TSH (thyroid stimulating hormone or thyrotropin) concentration in the blood is the test of choice to evaluate thyroid gland function in people. With primary hypothyroidism (the thyroid gland is the sight of dysfunction), the pituitary gland produces extra TSH to try to additionally stimulate the low functioning thyroid gland. Therefore, the measurement of high concentrations of TSH in a patient with low T4 and signs of hypothyroidism, would indicate that the patient has primary hypothyroidism. ( Dogs with secondary hypothyroidism, where the problem is a lack of secretion of TSH by the pituitary gland results in lack of stimulation of the thyroid gland are rare.) Unfortunately, the assay used to measure TSH in people can not be used to measure canine TSH, due to a species difference in the structure of the molecule. However, recently a species specific TSH assay for the dog has become commercially available. This assay can distinguish known hypothyroid dogs by measuring elevated TSH concentrations in the hypothyroid dogs when compared to TSH concentrations measured in clinically normal dogs. After limited use in practice (over 200 samples during 6 months), the authors have found the TSH concentration to be a valuable tool, when used with the measurement of free T4 concentration, in assessing thyroid function in dogs.

CIRCULATING ANTIBODIES AGAINST THYROGLOBULIN
When hypothyroidism is due to lymphocytic thyroiditis, the dog's body may produce antibodies to a protein portion of the thyroid hormone molecule called thyroglobulin. As many as 60% of hypothyroid dogs tested for thyroglobulin antibodies were positive; however, normal dogs may also have thyroglobulin antibodies but at a much lower incidence. The measurement of thyroglobulin antibodies has the potential value of early recognition of lymphocytic thyroiditis. This test is only available at the College of Veterinary Medicine at the University of Florida.

CIRCULATING ANTIBODIES AGAINST THYROID HORMONES
In addition to forming antibodies against thyroglobulin, dogs with hypothyroidism due to lymphocytic thyroiditis can also produce antibodies against thyroid hormones (T3 & T4). Thyroid hormone antibodies can also occur in normal dogs. Besides indicating that the process of lymphocytic thyroiditis may be occurring, the presence of thyroid hormone antibodies may result in elevations in the measurement of TT3 and TT4. Measurement of free T4 by equilibrium dialysis will show normal concentrations early in the immune-mediated process before clinical hypothyroidism is apparent. As thyroid gland tissue is destroyed by the lymphocytic thyroiditis, thyroid gland function decreases, free T4 concentrations decrease and the dog shows clinical signs of hypothyroidism. The measurement of thyroid hormone antibodies is available at certain veterinary laboratories across the country.

THYROID BIOPSY
A surgical biopsy of the thyroid gland can be taken to evaluate the pathological process occurring in the thyroid gland. Cellular changes such as lymphocyte infiltration or follicle atrophy can be defined by microscopic examination of the thyroid biopsy. The advantage to biopsy is that it is specific for thyroid disease and can detect early changes even before significant decreases in circulating blood hormone concentrations. However, the degree of thyroid pathology observed microscopically may not necessarily parallel thyroid production of hormones or clinical hypothyroidism. Thyroid biopsy can be helpful in distinguishing primary hypothyroidism (defect is the thyroid gland) from secondary hypothyroidism (lack of stimulation of the thyroid gland by lack of TSH from the pituitary gland). Thyroid biopsy requires surgery and anesthesia and is moderately expensive ($75.00-$150.00)

In summary, definitive diagnosis of hypothyroidism can best be made at this time by a combination of abnormal specific thyroid test results coupled with successful long term response to thyroxine supplementation. The ideal tests currently available seem to be either a TSH stimulation test or when not available or affordable, a free T4 concentration by equilibrium dialysis, with or without a cholesterol measurement. Measurement of TSH concentration, along with measurement of free T4 concentration, are currently the diagnostic tests of choice in evaluating thyroid function in the dog. Caution should be made in over-interpretation of any thyroid function tests in clinically ill dogs. References 1. Beale KM, Halliwell REW, Chen CL. Prevalence of antithyroglobulin antibodies detected by enzyme-linked immunosorbent assay of canine serum, Journal of the American Veterinary Medical Association, 196 (5), March 1, 1990. 2. Ferguson DC, Peterson ME. Serum free and total iodothyronine concentrations in dogs with hyperadrenocorticism, American Journal of Veterinary Research, 53 (9), September, 1992. 3. Ferguson DC. Update on the diagnosis of canine hypothyroidism, The Veterinary Clinics of North America: Small Animal Practice, Thyroid Disorders, 24 (3), May, 1994. 4. Hall IA, Campbell KL, Chambers MD, Davis CN. Effect of trimethoprim/ sulfamethoxazole on thyroid function in dogs with pyoderma, Journal of the American Veterinary Medical Association, 202 (12), June 15, 1993. 5. Kemppainen RJ, Clark TP. Etiopathogenesis of canine hypothyroidism, The Veterinary Clinics of North America: Small Animal Practice, Thyroid Diseases, 24 (3), May, 1994. 6. Moore GE, Ferguson DC, Hoenig M. Effects of oral administration of anti-inflammatory doses of prednisone on thyroid hormone response to thyrotropin-releasing hormone and thyrotropin in clinically normal dogs, American Journal of Veterinary Research, 54 (1), January 1993. 7. Reimers TJ, Lawler EF, Sutaria PM, Correa MT, Erb HN. Effects of age, sex, and body size on serum concentrations of thyroid and adrenocortical hormones in dogs, American Journal of Veterinary Research, 51 (3), March 1990. 8. Williams D, Scott-Moncrieff JC, Bruner J. Canine serum thyroid-stimulating hormone following induction of hypothyroidism, American Journal of Veterinary Internal Medicine, Abstract from Proceedings of ACVIM, Orlando, May 18, 1995, 9(3), May /June 1995.

TABLE 1

THYROID TESTS FOR DOGS
TEST ADVANTAGES LIMITATIONS
TT3 Simple, Inexpensive Does not reflect thyroid function
TT4 Simple, Inexpensive Can be falsely low due to drugs or non-thyroid illness
FREE T4 Better reflects true thyroid function Relatively expensive
TSH STIMULATION Currently the best indicator of thyroid function because it measures thyroid gland response to stimulation Cost & Availability
TRH STIMULATION Also measures thyroid gland response to stimulation but harder to interpret Cost & Availability
Side Effects
TSH CONCENTRATION Potentially may be best indicator of thyroid gland function when used with Free T4 Limited use so far; moderately expensive
THYROGLOBULIN ANTIBODIES Early detection; Specific for immune-mediated thyroid involvement Can be positive in normal dogs; Currently available at Southwest Veterinary Diagnostics, Inc., Phoenix, Arizona
THYROID HORMONE ANTIBODIES Early detection; Specific for immune-mediated thyroid involvement Can be positive in normal dogs; Available at Michigan State University
THYROID BIOPSY Demonstrates specific thyroid involvement; distinguishes primary from secondary hypothyroidism Cost, surgery, anesthesia; May not reflect degree of thyroid dysfunction


http://www.siriusdog.com/thyroid-test-dogs-t3-t4.htm

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Postby Allie » Tue Feb 03, 2009 8:59 pm

Thanks! :bowdown:

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Postby Misskiwi67 » Wed Feb 04, 2009 1:08 am

The in-house snap test is a Total T4 ONLY... it is used as a screening test and should not be used as a sole diagnostic test for thyroid function.

If the snap test is low, do not start supplementation without a full thyroid panel, or a TSH at minimum.

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Postby Murfins » Wed Feb 04, 2009 6:06 am

Both my cat (hyperthyroidism) and my dog (hypothyroidism) were diagnosed fairly recently through geriatric panel bloodwork and then confirmed through more indepth tests (I cannot seem to find their vet bills that show the exact names of the tests).

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Postby Allie » Wed Feb 04, 2009 6:13 am

Thank you.
Should I have him do this in house T4 and send the rest out, or just send it all out?

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Postby Maryellen » Wed Feb 04, 2009 7:56 am

way to go Pblove!! :bowdown:

i would have him do it all, just to be sure..

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Postby pblove » Wed Feb 04, 2009 9:02 am

Allie wrote:Thank you.
Should I have him do this in house T4 and send the rest out, or just send it all out?

Allie if you go to the link I posted it will tell you what tests can and/or should be sent out andwhy or why not, it is at the bottoem of the page in a chart.

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Postby Allie » Wed Feb 04, 2009 10:01 am

Maryellen wrote:way to go Pblove!! :bowdown:

i would have him do it all, just to be sure..

I mean if he can't do all of them, only the T4


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