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College of Health Sciences
Department of Medical Laboratories
Third Year – Second Term
Hormones
Practice NO (1)
Determination of Thyroid Hormones
Hyper- and hypofunction
Imbalance in production of thyroid hormones arises from disfunction of
the thyroid gland itself, the pituitary gland, which produces thyroidstimulating hormone (TSH), or the hypothalamus, which regulates the
pituitary gland via thyrotropin-releasing hormone (TRH).
Concentrations of TSH increase with age, requiring age-corrected tests
Hypothyroidism affects between three and ten percent of adults, with
incidence higher in women and the elderly. Hypothyroidism
(underactivity)
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Hashimoto's thyroiditis / thyroiditis
Ord's thyroiditis
Postoperative hypothyroidism
Postpartum thyroiditis
Silent thyroiditis
Acute thyroiditis
Iatrogenic hypothyroidism
Thyroid hormone resistance
Euthyroid sick syndrome
Hyperthyroidism (overactivity)
o Thyroid storm
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Graves' disease
Toxic thyroid nodule
Toxic nodular struma (Plummer's disease)
Hashitoxicosis
Iatrogenic hyperthyroidism
De Quervain's thyroiditis (inflammation starting as
hyperthyroidism, can end as hypothyroidism)
Anatomical problems
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Goitre
o Endemic goitre
o Diffuse goitre
o Multinodular goitre
Lingual thyroid
Thyroglossal duct cyst
Tumors
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Thyroid adenoma
Thyroid cancer
o Papillary
o Follicular
o Medullary
o Anaplastic
Lymphomas and metastasis from elsewhere (rare)
Deficiencies
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Cretinism
Medication linked to thyroid disease includes amiodarone, lithium salts,
some types of interferon and IL-2.
Diagnosis
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Blood tests
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The measurement of thyroid-stimulating hormone (TSH) levels is
often used by doctors as a screening test. Elevated TSH levels can
signify an inadequate thyroid hormone production, while
suppressed levels can point at excessive unregulated production
of hormone.
If TSH is abnormal, decreased levels of thyroid hormones T4 and
T3 may be present; T4 and T3 levels may be determined with
blood tests to confirm that their levels are decreased.
Autoantibodies may be detected in various disease states (antiTG, anti-TPO, TSH receptor stimulating antibodies).
There are two cancer markers for thyroid derived cancers.
Thyroglobulin (TG) for well differentiated papillary or follicular
adenocarcinoma, and the rare medullary thyroid cancer has
calcitonin as the marker.
Very infrequently, TBG and transthyretin levels may be abnormal;
these are not routinely tested.
To differentiate between different types of hypothyroidism, a
specific test may be used. Thyroid-releasing hormone (TRH) is
injected into the body through a vein. This hormone is naturally
secreted by the hypothalamus and stimulates the pituitary gland.
The pituitary responds by releasing thyroid -stimulating hormone
(TSH). Large amounts of externally administered TRH can suppress
the subsequent release of TSH. This amount of releasesuppression is exaggerated in primary hypothyroidism, major
depression, cocaine dependence, amphetamine dependence and
chronic phencyclidine abuse. There is a failure to suppress in the
manic phase of bipolar disorder. Radioiodine scanning and uptake
Thyroid scintigraphy, imaging of the thyroid with the aid of radioactive
iodine, usually iodine-123, is performed in the nuclear medicine
department of a hospital or clinic. Radioiodine collects in the thyroid
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gland before being excreted in the urine. While in the thyroid the
radioactive emissions can be detected by a camera, producing a rough
image of the shape (a radiodine scan) and tissue activity (a radioiodine
uptake) of the thyroid gland.
A normal radioiodine scan shows even uptake and activity throughout
the gland. Irregularity can reflect an abnormally shaped or abnormally
located gland, or it can indicate that a portion of the gland is overactive
or underactive, different from the rest. For example, a nodule that is
overactive ("hot") to the point of suppressing the activity of the rest of
the gland is usually a thyrotoxic adenoma, a surgically curable form of
hyperthyroidism that is hardly ever malignant. In contrast, finding that a
substantial section of the thyroid is inactive ("cold") may indicate an
area of non-functioning tissue such as thyroid cancer.
The amount of radioactivity can be counted as an indicator of the
metabolic activity of the gland. A normal quantitation of radioiodine
uptake demonstrates that about 8 to 35% of the administered dose can be
detected in the thyroid 24 hours later. Overactivity or underactivity of
the gland as may occur with hypothyroidism or hyperthyroidism is
usually reflected in decreased or increased radioiodine uptake. Different
patterns may occur with different causes of hypo- or hyperthyroidism.
How is a thyroid panel used?
A thyroid panel is used to screen for or help diagnose hypo- and
hyperthyroidism due to various thyroid disorders.
The preferred test to screen for thyroid disorders is a TSH test. If
your TSH level is abnormal, it will usually be followed up with a
test for total T4 or free T4. Sometimes a total T3 or free T3 will also
be performed. Often, the laboratory will do this follow-up testing
automatically, and this is known as reflex testing. This saves your
doctor time from having to wait for the results of the initial test and
then requesting the additional testing to confirm or clarify a
diagnosis. Follow-up tests are often performed on the original
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sample that was submitted when the initial test was requested. A
thyroid panel may be requested by your doctor to have all three
tests performed at the same time to get a more complete picture.
When is it ordered?
A thyroid panel may be ordered as part of a health checkup or
when symptoms suggest hypo- or hyperthyroidism due to a
condition affecting the thyroid.
Signs and symptoms of hypothyroidism may include weight gain,
dry skin, constipation, cold intolerance, puffy skin, hair loss,
fatigue, and menstrual irregularity in women.
Signs and symptoms of hyperthyroidism may include increased
heart rate, anxiety, weight loss, difficulty sleeping, tremors in the
hands, weakness, and sometimes diarrhea. There may be
puffiness around the eyes, dryness, irritation, and, in some cases,
bulging of the eyes.
What do the test results mean?
If the feedback system involving the thyroid gland is not functioning
properly due to one of a variety of disorders, then increased or
decreased amounts of thyroid hormones may result. When TSH
concentrations are increased, the thyroid will make and release
inappropriate amounts of T4 and T3, and the patient may
experience symptoms associated with hyperthyroidism. If there is
decreased production of thyroid hormones, the patient may
experience symptoms of hypothyroidism.
The following table summarizes test results and their potential
meaning.
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TSH
T4
T3
INTERPETATION
High Normal
Normal
Mild (subclinical) hypothyroidism
High Low
Low or
normal
Hypthyroidism
Low Normal
Normal
Mild (subclinical) hyperthyroidism
Low High or
normal
High or
normal
Hyperthyroidism
Low Low or
normal
Low or
normal
Nonthyroidal illness; rare pituitary
(secondary) hypothyroidism
Is there anything else I should know?
In the past, panels of tests were more common. More recently,
however, the practice is to order, where possible, one initial or
screening test and then follow up with additional testing, if
needed, to reduce the number of unnecessary tests. With thyroid
testing, one strategy is to screen with a TSH test and, if the
results are abnormal, then order additional tests. Many
laboratories still perform thyroid panels, but this will become less
common in the future as better screening strategies are
developed.
1. What conditions are associated with hypo- and
hyperthyroidism?
The most common causes of thyroid dysfunction are
autoimmune-related. Graves’ disease causes hyperthyroidism,
and Hashimoto’s thyroiditis causes hypothyroidism. Both hyperPrepared By Dr. Abdelrahman Elreshid 6
and hypothyroidism can also be caused by thyroiditis, thyroid
cancer, and excessive or deficient production of TSH.
2. What other tests may be ordered in addition to a thyroid
panel?
Tests that may be performed in addition to a thyroid panel may
include:
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Thyroid antibodies - to help differentiate different types of
thyroiditis and identify autoimmune thyroid conditions
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Calcitonin - to help detect the presence of excessive
calcitonin production
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Thyroglobulin - to monitor treatment of thyroid cancer
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Thyroxine-binding globulin (TBG) - to evaluate patients with
abnormal T4 and T3 levels
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