Common Thyroid Problems
Thyroid Gland Function
TSH / T3 / FT3 / T4 /
Normal Laboratory Values
The thyroid gland is the biggest gland in the neck. It is situated in the
anterior (front) neck below the skin and muscle layers. The thyroid gland
takes the shape of a butterfly with the two wings being represented by the
left and right thyroid lobes which wrap around the trachea. The sole
function of the thyroid is to make thyroid hormone. This hormone has an
effect on nearly all tissues of the body where it increases cellular activity. The function of the thyroid therefore is
to regulate the body's metabolism.
thyroid cancer tumor surgery operation
condition thyroid parathyroid disease disease tumor
thyroid gland is a small gland, normally weighing less than one ounce,
located in the front of the neck. It is made up of two halves, called lobes,
that lie along the windpipe (trachea) and are joined together by a narrow
band of thyroid tissue, known as the isthmus.
The thyroid is situated just below your "Adams apple" or larynx.
During development (inside the womb) the thyroid gland originates in the
back of the tongue, but it normally migrates to the front of the neck before
birth. Sometimes it fails to migrate properly and is located high in the
neck or even in the back of the tongue (lingual thyroid) This is very rare.
At other times it may migrate too far and ends up in the chest (this is also
function of the thyroid gland is to take iodine, found in many foods, and
convert it into thyroid hormones: thyroxine
(T4) and triiodothyronine (T3). Thyroid cells are the only cells
in the body which can absorb iodine. These cells combine iodine and the
amino acid tyrosine to make T3 and T4. T3 and T4 are then released
into the blood stream and are transported throughout the body where they
control metabolism (conversion of oxygen and calories to energy). Every
cell in the body depends upon thyroid hormones for regulation of their
metabolism. The normal thyroid gland produces about 80% T4 and about 20%
T3, however, T3 possesses about four times the hormone "strength"
thyroid gland is under the control of the pituitary gland, a
small gland the size of a peanut at the base of the brain (shown here in
orange). When the level of thyroid hormones (T3 & T4) drops too low, the
pituitary gland produces Thyroid Stimulating Hormone
(TSH) which stimulates the thyroid gland to produce more
hormones. Under the influence of TSH, the thyroid will manufacture and
secrete T3 and T4 thereby raising their blood levels. The pituitary senses
this and responds by decreasing its TSH production. One can imagine the
thyroid gland as a furnace and the pituitary gland as the thermostat.
Thyroid hormones are like heat. When the heat gets back to the thermostat,
it turns the thermostat off. As the room cools (the thyroid hormone levels
drop), the thermostat turns back on (TSH increases) and the furnace produces
more heat (thyroid hormones).
pituitary gland itself is regulated by another gland, known as the
hypothalamus (shown in our picture in light blue). The
hypothalamus is part of the brain and produces TSH
Releasing Hormone (TRH) which tells the pituitary gland to
stimulate the thyroid gland (release TSH). One might imagine the
hypothalamus as the person who regulates the thermostat since it tells the
pituitary gland at what level the thyroid should be set.
thyroid gland is prone to several very distinct problems, some of which are
extremely common. These problems can be broken down into 
those concerning the production of hormone (too much, or too little), 
those due to increased growth of the thyroid causing compression of
important neck structures or simply appearing as a mass in the neck, 
the formation of nodules or lumps within the thyroid which are worrisome for
the presence of thyroid cancer, and  those
which are cancerous. Each thyroid topic is addressed separately and
illustrated with actual patient x-rays and pictures to make them easier to
understand. The information on this web site is arranged to give you more
detailed and complex information as you read further.
~ A thyroid goiter is a dramatic enlargement of the thyroid gland. Goiters
are often removed because of cosmetic reasons or, more commonly, because
they compress other vital structures of the neck including the trachea and
the esophagus making breathing and swallowing difficult. Sometimes goiters
will actually grow into the chest where they can cause trouble as well.
Several nice x-rays will help explain all types of thyroid goiter problems.
Cancer ~ Thyroid cancer is a fairly common malignancy,
however, the vast majority have excellent long term survival. We now include
a separate page on the characteristics of each type of thyroid cancer and
its typical treatment, follow-up, and prognosis. Over
30 pages thyroid cancer.
Thyroid Nodules ~ There are several characteristics of
solitary nodules of the thyroid which make them suspicious for malignancy.
Although as many as 50% of the population will have a nodule somewhere in
their thyroid, the overwhelming majority of these are benign. Occasionally,
thyroid nodules can take on characteristics of malignancy and require either
a needle biopsy or surgical excision. Now includes risks
of radiation exposure and the role of Needle Biopsy for evaluating a thyroid
nodule. Also a new page on the role of ultrasound in diagnosing
thyroid nodules and masses.
~ Hyperthyroidism means too much thyroid hormone. Current methods used for
treating a hyperthyroid patient are radioactive iodine, anti-thyroid drugs,
or surgery. Each method has advantages and disadvantages and is selected for
individual patients. Many times the situation will suggest that all three
methods are appropriate, while other circumstances will dictate a single
best therapeutic option. Surgery is the least common treatment selected for
hyperthyroidism. The different causes of hyperthyroidism are covered in
~ Hypothyroidism means too little thyroid hormone and is a common problem.
In fact, hypothyroidism is often present for a number of years before it is
recognized and treated. There are several common causes, each of which are
covered in detail. Hypothyroidism can even be associated with pregnancy.
Treatment for all types of hypothyroidism is usually straightforward.
~ Thyroiditis is an inflammatory process ongoing within the thyroid gland.
Thyroiditis can present with a number of symptoms such as fever and pain,
but it can also present as subtle findings of hypo or hyper-thyroidism.
There are a number of causes, some more common than others. Each is covered
on this site.
Some information on this page is a
little more advanced.
If you have trouble understanding the process of normal
please go to our page describing this process first.
As we have seen from our overview
of normal thyroid physiology, the thyroid gland produces T4 and T3. But
this production is not possible without stimulation from the pituitary gland
(TSH) which in turn is also regulated by the hypothalamus's TSH Releasing
Hormone. Now, with radioimmunoassay techniques it is possible to measure
circulating hormones in the blood very accurately. Knowledge of this thyroid
physiology is important in knowing what thyroid test or tests are needed to
diagnose different diseases. No one single laboratory test is 100% accurate
in diagnosing all types of thyroid disease; however, a
combination of two or more tests can usually detect even the slightest
abnormality of thyroid function.
For example, a
low T4 level could mean a diseased thyroid gland ~ OR ~ a
non-functioning pituitary gland which is not stimulating the thyroid to
produce T4. Since the pituitary gland would normally release TSH if the T4
is low, a high TSH level would confirm that the thyroid gland (not the
pituitary gland) is responsible for the hypothyroidism.
the T4 level is low and TSH is not elevated, the pituitary gland
is more likely to be the cause for the hypothyroidism. Of course, this would
drastically effect the treatment since the pituitary
gland also regulates the body's other glands (adrenals, ovaries, and
testicles) as well as controlling growth in children and normal kidney
function. Pituitary gland failure means that the other glands may also be
failing and other treatment than just thyroid may be necessary. The most
common cause for the pituitary gland failure is a tumor of the pituitary and
this might also require surgery to remove.
- Modern measurement of thyroid hormones is done by a new
technique, radioimmunoassay (RIA), discovered by Dr. Solomon Berson and Dr.
Rosalyn Yallow. They were awarded the 1977 Nobel Prize in Medicine for this
discovery which revolutionized the study of thyroid disease as well as the
entire field of endocrinology.
following are commonly used thyroid tests
of Serum Thyroid Hormones: T4 by RIA. T4 by RIA (radioimmunoassay)
is the most used thyroid test of all. It is frequently referred to as a T7
which means that a resin T3 uptake (RT3u) has been done to correct for
certain medications such as birth control pills, other hormones, seizure
medication, cardiac drugs, or even aspirin that may alter the routine T4
test. The T4 reflects the amount of thyroxine in the blood. If the
patient does not take any type of thyroid medication, this test is
usually a good measure of thyroid function.
of Serum Thyroid Hormones: T3 by RIA. As stated on our
thyroid hormone production page, thyroxine (T4) represents 80% of the
thyroid hormone produced by the normal gland and generally represents the
overall function of the gland. The other 20% is triiodothyronine measured
as T3 by RIA. Sometimes the diseased thyroid gland will start producing
very high levels of T3 but still produce normal levels of T4. Therefore
measurement of both hormones provides an even more accurate evaluation of
Binding Globulin. Most of the thyroid hormones in the blood are
attached to a protein called thyroid binding globulin (TBG). If there is an
excess or deficiency of this protein it alters the T4 or T3 measurement
but does not affect the action of the hormone. If a patient
appears to have normal thyroid function, but an unexplained high or low T4,
or T3, it may be due to an increase or decrease of TBG. Direct measurement
of TBG can be done and will explain the abnormal value. Excess TBG or low
levels of TBG are found in some families as an hereditary trait. It causes
no problem except falsely elevating or lowering the T4 level. These people
are frequently misdiagnosed as being hyperthyroid or hypothyroid, but they
have no thyroid problem and need no treatment.
of Pituitary Production of TSH. Pituitary production of
TSH is measured by a method referred to as IRMA (immunoradiometric assay).
Normally, low levels (less than 5 units) of TSH are sufficient to keep the
normal thyroid gland functioning properly. When the thyroid gland becomes
inefficient such as in early hypothyroidism, the TSH becomes elevated even
though the T4 and T3 may still be within the "normal" range. This
rise in TSH represents the pituitary gland's response to a drop in
circulating thyroid hormone; it is usually the first indication of thyroid
gland failure. Since TSH is normally low when the thyroid gland is
functioning properly, the failure of TSH to rise when circulating thyroid
hormones are low is an indication of impaired pituitary function. The new
"sensitive" TSH test will show very low levels of TSH when the
thyroid is overactive (as a normal response of the pituitary to try to
decrease thyroid stimulation). Interpretations of the TSH level depends
upon the level of thyroid hormone; therefore, the TSH is usually used in
combination with other thyroid tests such as the T4 RIA and T3 RIA.
information about TSH Test
Test. In normal people TSH secretion from the pituitary
can be increased by giving a shot containing TSH Releasing Hormone
(TRH...the hormone released by the hypothalamus which tells the pituitary to
produce TSH). A baseline TSH of 5 or less usually goes up to 10-20 after
giving an injection of TRH. Patients with too much thyroid hormone (thyroxine
or triiodothyronine) will not show a rise in TSH when given TRH. This
"TRH test" is presently the most sensitive test in detecting early
hyperthyroidism. Patients who show too much response to TRH (TSH rises
greater than 40) may be hypothyroid. This test is also used in cancer
patients who are taking thyroid replacement to see if they are on sufficient
medication. It is sometimes used to measure if the pituitary gland is
functioning. The new "sensitive" TSH test (above) has
eliminated the necessity of performing a TRH test in most clinical
information about TRH Test
Uptake Scan. A means of measuring thyroid function is to
measure how much iodine is taken up by the thyroid gland (RAI uptake).
Remember, cells of the thyroid normally absorb iodine from our blood stream
(obtained from foods we eat) and use it to make thyroid hormone (described
on our thyroid
function page). Hypothyroid patients usually take up too little iodine
and hyperthyroid patients take up too much iodine. The test is performed by
giving a dose of radioactive iodine on an empty stomach. The iodine is
concentrated in the thyroid gland or excreted in the urine over the next few
hours. The amount of iodine that goes into the thyroid gland can be measured
by a "Thyroid Uptake". Of course, patients who are taking thyroid
medication will not take up as much iodine in their thyroid gland because
their own thyroid gland is turned off and is not functioning. At other times
the gland will concentrate iodine normally but will be unable to convert the
iodine into thyroid hormone; therefore, interpretation of the iodine uptake
is usually done in conjunction with blood tests.
Scan. Taking a "picture" of how well the thyroid gland
is functioning requires giving a radioisotope to the patient and letting the
thyroid gland concentrate the isotope (just like the iodine uptake scan
above). Therefore, it is usually done at the same time that the iodine
uptake test is performed. Although other isotopes, such as technetium,
will be concentrated by the thyroid gland; these isotopes will not measure
iodine uptake which is what we really want to know because the production of
thyroid hormone is dependent upon absorbing iodine. It has also been found
that thyroid nodules that concentrate iodine are rarely cancerous; this is
not true if the scan is done with technetium. Therefore, all scans are now
done with radioactive iodine. Both of the scans above show normal sized
thyroid glands, but the one on the left has a "HOT"
nodule in the lower aspect of the right lobe, while the scan on the right
has a "COLD" nodule in the lower aspect
of the left lobe (outlined in red and yellow). Pregnant women should not
have thyroid scans performed because the iodine can cause development
troubles within the baby's thyroid gland.
- Two types of thyroid scans are available. A camera scan
is performed most commonly which uses a gamma camera operating in a fixed
position viewing the entire thyroid gland at once. This type of scan takes
only five to ten minutes. In the 1990's, a new scanner called a Computerized
Rectilinear Thyroid (CRT) scanner was introduced. The CRT scanner utilizes
computer technology to improve the clarity of thyroid scans and enhance
thyroid nodules. It measures both thyroid function and thyroid size. A
life-sized 1:1 color scan of the thyroid is obtained giving the size in
square centimeters and the weight in grams. The precise size and activity of
nodules in relation to the rest of the gland is also measured. CTS of the
normal thyroid gland In addition to making thyroid diagnosis more accurate,
the CRT scanner improves the results of thyroid biopsy. The accurate sizing
of the thyroid gland aids in the follow-up of nodules to see if they are
growing or getting smaller in size. Knowing the weight of the thyroid gland
allows more accurate radioactive treatment in patients who have Graves'
Thyroid Scans are used for
the following reasons:
and determining if they are
"hot" or "cold".
Measuring the size of the
goiter prior to treatment.
Follow-up of thyroid cancer
patients after surgery.
Locating thyroid tissue
outside the neck, i.e. base of the
tongue or in the chest.
Ultrasound. Thyroid ultrasound refers to the use of high
frequency sound waves to obtain an image of the thyroid gland and identify
nodules. It tells if a nodule is "solid" or a fluid-filled cyst,
but it will not tell if a nodule is benign or malignant. Ultrasound allows
accurate measurement of a nodule's size and can determine if a nodule is
getting smaller or is growing larger during treatment. Ultrasound aids in
performing thyroid needle biopsy by improving accuracy if the nodule cannot
be felt easily on examination. Several more pages are dedicated to the use
of ultrasound in evaluating thyroid nodules.
Antibodies. The body normally produces antibodies to foreign
substances such as bacteria; however, some people are found to have
antibodies against their own thyroid tissue. A condition known as Hashimoto's
Thyroiditis is associated with a high level of these thyroid antibodies
in the blood. Whether the antibodies cause the disease or whether the
disease causes the antibodies is not known; however, the finding of a high
level of thyroid antibodies is strong evidence of this disease.
Occasionally, low levels of thyroid antibodies are found with other types of
thyroid disease. When Hashimoto's thyroiditis presents as a thyroid nodule
rather than a diffuse goiter, the thyroid antibodies may not be present.
Needle Biopsy. This has become the most reliable test to
differentiate the "cold" nodule that is cancer from the
"cold" nodule that is benign ("hot" nodules are rarely
cancerous). It provides information that no other thyroid test will provide.
While not perfect, it will provide definitive information in 75% of the
nodules biopsied. A very extensive discussion of Thyroid
Needle Biopsy is found on another page.
Do I need to stop taking my thyroid pills for these tests?
Since Euthyrox or
Synthroid (and most other thyroid pills) behave exactly as normal human
thyroid hormone, they are not rapidly cleared from the body as other
medications are. Most thyroid pills have a half life of 6.7 days which means
they must be stopped for four to five weeks (five half lives) before
accurate thyroid testing is possible. An exception to the long half life of
thyroid medication is Cytomel - a thyroid pill with a half life of only
forty-eight hours. Therefore it is possible to change a person's thyroid
replacement to Cytomel for one month to allow time for his regular pills to
clear the body. Cytomel is then stopped for ten days (five half lives) and
the appropriate test can then be done. Usually patients, even those who have
no remaining thyroid function, tolerate being off thyroid replacement only
ten days quite well.
|Free Thyroxine index
|Free T3 Index
ug/dl T4 +1.8 ugm
|TRH stimulation test
uIU/ml at 20-30 min
|Serum thyroglobulin l
TSH (Thyroid Stimulation Hormone)
Specimen Required: 2 mL blood. Plain tube
Minimum Referred Volume: 0.4 mL serum
Reference Interval: 0.3 - 4.0 mU/L
Imprecision: ? 5%
Turnaround Time: 1 day
How the Test is Performed:
Adult or child:
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
Why this Test is Performed:
TSH is measured to differentiate primary versus secondary hyperthyroidism or hypothyroidism . Primary hypothyroidism , for example, results from decreased production of T3 and T4 by the thyroid gland in spite of normal or increased stimulation by
TSH. Secondary hypothyroidism results from decreased production of T3 and T4 as a result of decreased secretion of TSH from the pituitary gland.
TSH is secreted by the pituitary and stimulates secretion of T4 and T3 from the thyroid gland. TSH is, itself, stimulated by TRH, which is released by the hypothalamus . T3 and T4 feedback inhibit the release of both TSH and TRH in normal people.
0.2 to 4.7 mcU/ml
Note: mcU/ml = microunits per milliliter
Greater-than-normal levels may indicate:
congenital hypothyroidism (cretinism)
Lower-than-normal levels may indicate:
Additional conditions under which the test may be performed:
colloid nodular goiter
multiple endocrine neoplasia (MEN) I
thyrotoxic periodic paralysis
toxic nodular goiter
Drugs that can increase TSH measurements include antithyroid medications, lithium, and potassium iodide.
Drugs that can decrease TSH measurements include aspirin, dopamine , heparin, and
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
[Q&As are placed in reverse chronological order. In other words,
the latest Q&As come first. Earlier ones are further down the page.]
Date: April 12, 2000
Question: Mary Shomon recommended your website for information on problems with the conversion of thyroid hormone. I have most of the symptoms on a checklist for hypothyroidism. Interestingly, two doctors told me that some of my symptoms are
fibromyalgia, but they dont know the cause of my other symptoms. To me, all the symptoms could be hypothyroidism or the problem converting T4 to T3 that Dr. Dennis Wilson writes about. Hypothyroidism is common in my family. However, my doctor has ordered TSH and T4 levels twice, and both times the levels were normal. Since my lab tests are normal, does this mean my
"hypothyroid"symptoms are caused by a conversion problem?
Dr. Lowe: Nothe clinical picture you describe (normal TSH and T4 levels in someone with hypothyroid-like symptoms) does not necessarily point to a problem in converting T4 to T3. In fact, it is highly unlikely that impaired conversion is the problem. Instead, you may be hypothyroid despite normal TSH and T4 test results. Bear in mind the definition of hypothyroidism: lower-than-normal blood levels of thyroid hormone due to an underactive thyroid gland. Our TSH and thyroid hormone levels vary during the day and from day-to-day during the week. Its possible that when you were tested, your TSH and T4 levels were within the normal range, but that the levels are abnormal at other times. As a result, on average, your tissue may have too little stimulation by thyroid hormone. Also, recent evidence suggests that the so-called "normal" ranges may be too wide. As a result, some peoples doctors may believe their test results are normal when in fact the patients are hypothyroid.
In addition, you might have central hypothyroidism. In central hypothyroidism, the thyroid gland is
underactive. As a result, the blood level of thyroid hormone is too low, at least part of the time. But the cause of the underactive thyroid gland and low thyroid hormone level is not an abnormality of the thyroid gland. Instead, the cause is a dysfunction of the pituitary gland or hypothalamus. When a patients standard thyroid test results are normal, the doctor should always consider the possibility of central hypothyroidism. The best way to test for this form of hypothyroidism is the TRH stimulation test. With this test, we identify many patients whore hypothyroid, although their standard thyroid test results are normal.
Some patients do have impaired conversion of T4 to T3. However, the available scientific evidence suggests that at the longest, impaired conversion lasts only a few weeks. I know of no scientific evidence supporting Dr. Dennis Wilsons speculation that some patients have chronically impaired conversion of T4 to T3. When patients have impaired T4 to T3 conversion, they also have a predictable pattern of lab test results. However, despite extensive testing, one other researcher and I have never found this predictable lab test pattern in fibromyalgia outpatients.
Date: April 15, 1998
QuestionPart 1: I am a 44-year old male diagnosed with fibromyalgia four years ago. About two years ago my chiropractor brought to my attention your work relating hypothyroidism with
fibromyalgia. My family doctor was curious so he ordered T4 and TSH tests which both come back normal, but both at the very low-normal end (T4 = 0.70; TSH = 0.44). I took the tests to an internist who dismissed my thyroid tests as normal. At my insistence, he referred me to an endocrinologist who was curious about your work, but he also thought my thyroid tests were normal. He did order the TRH and CRH stimulation tests, which both came out "normal." However, my TSH during the TRH test only reached a maximum of 6.8. Isn't this a "blunted" response?
Dr. Lowe: Yes, your TSH response of 6.8 ตIU/mL was blunted. (The range of normal for the TSH level 30 minutes following a TRH injection is 8.5-to-20.0 ตIU/mL above the baseline TSH value.) My conclusion, however, isn't based only on the result of your TRH stimulation test. Both your T4 and baseline TSH levels were low (and in later testing, your T3 was also low). It is abnormal for your TSH level also to be low when your T4 and T3 levels are low. Normally, the TSH level is inversely related to the T4 and T3 levels: When the T4 and T3 levels are low, a "normal" anterior pituitary gland increases its output of
That your TSH level was low despite your low T4 and T3 levels suggests that your pituitary gland is not able to synthesize and secrete normal amounts of
TSH. This was confirmed by your TRH stimulation test. TRH, a hormone secreted by the hypothalamus, stimulates your pituitary gland to secrete
TSH. When the T4 level is low, an injection of TRH causes a normal pituitary gland to secrete an unusually large amount of
TSHan amount that exceeds the upper normal level of 20.0 ตIU/mL. The failure of your pituitary gland to secrete this increased amount in response to the TRH injection supports the hypothesis that your pituitary gland is not able to synthesize and secrete normal amounts of
TSH. It is highly probable that your low T4, T3, and baseline TSH levels were all a result of a pituitary abnormality. That you were hypothyroid is indicated by your symptoms and your positive response to exogenous T4 and T3 (see below). The appropriate diagnosis, as your endocrinologist later concluded, is central (more specifically, pituitary) hypothyroidism.