Lab Assesment of Thyroid Function

Hyperthyroidism may be referred to as

"thyrotoxicosis" or toxic levels of thyroid hormone being produced.

At-risk population for hypothyroidism

-Female over age 60 -Family history -Other autoimmune disorders -Type I diabetes -Arthritis -Pregnancy within 6 months -Received neck or chest radiation treatment -Previous neck or throat surgery -Living where iodine is deficient in environment

Primary hypothyroidism

-Related to the THYROID itself -Autoimmune interference with production -Insufficient supplies to make the hormones -Defective or blocked receptors -Faulty processing of hormone synthesis

Secondary hypothyroidism

-Related to the pituitary or hypothalamus; lack of stimulus -Insufficient TSH production from pituitary (COMMON) -Insufficient thyrotropin-releasing hormone (TRH) production from hypothalamus (rare)

Why would an excessive production of thyroid hormone cause the level of TSH to be low?

A negative feedback loop exists that tells the pituitary to stop producing TSH when thyroid hormones are found in excess

In the thyroid hormone feedback mechanism, what is the normal effect of T4 on thyroid-stimulating hormone (TSH) production?

Elevated T4 provides a negative feedback on TSH production.

Which of the following are considered among the classic symptoms of hypothyroidism?

Experiencing chronic fatigue and a lack of energy

Historical methods for determining the free thyroxine index (FTI) have been largely replaced with more sensitive and automated immunoassay methods for determining which hormone?

Free T4 (FT4)

Which of the following statements related to Graves' disease is TRUE?

Graves' disease is an autoimmune condition where the body produces increased amounts of thyroid hormone.

What common thyroid condition is associated with the production of the highest levels of thyroperoxidase antibody (TPOAb)?

Hashimoto's thyroiditis

Below are the laboratory results and chief clinical findings in a 31 year-old woman. Laboratory Results: Thyroid-stimulating hormone (TSH): 0.02 µIU/mL (ref range 0.4 - 4.12 µIU/mL) Free T3 (FT3): 6.8 pg/mL (ref range 2.5 - 3.9 pg/mL) Free T4 (FT4):1.6 ng/dL (ref range 0.6 - 1.3 ng/dL) Thyroperoxidase antibody (TPOAb): 10.4 IU/mL (ref range <9.0 IU/mL) Thyroglobulin antibody (TgAb): 5.5 IU/mL (ref range <4.0 IU/mL) Clinical Findings: Bulging eyes Hand tremors Extreme weight loss Accelerated heartbeat Which of the options below is most likely the diagnosis of this patient?

Hyperthyroidism, possibly due to Graves' disease; In Graves' disease, a hyperthyroid state results from the stimulation of the thyroid gland to produce hormone, absent the direct stimulation of TSH from the pituitary. In this case, there is evidence of an autoimmune process with TPOAb elevated, which although not diagnostic in itself for Graves' disease, indicates that anti-thyroid antibodies may be contributing to the findings of increased FT3 and highly decreased TSH.

Why is it important to screen expectant mothers for thyroid disorders early in pregnancy?

Insufficient levels of maternal thyroid hormones are associated with increased incidence of mental disabilities and decreased cognitive skills in newborns.

What form of triiodothyronine (T3) is formed in circulation under the influence of high stress in conjunction with elevated levels of cortisol?

Reverse T3 (RT3)

Below are the laboratory results and chief clinical findings in a 58 year-old woman. Laboratory Results: Thyroid-stimulating hormone (TSH): 4.21µIU/mL (ref range 0.4 - 4.12 µIU/mL) Free T3 (FT3): 2.5 pg/mL (ref range 2.5 - 3.9 pg/mL) Free T4(FT4): 1.0 ng/dL (ref range 0.6 - 1.3 ng/dL) Thyroperoxidase antibody (TPOAb): <1.0 IU/mL (ref range <9.0 IU/mL) Thyroglobulin antibody (TgAb): <0.5 IU/mL (ref range <4.0 IU/mL) Clinical Findings: Inability to lose weight Constipation

Subclinical hypothyroidism ;Mildly symptomatic patients found to have slightly elevated TSH levels, with FT3 and FT4 levels within expected limits, and the absence of detectable thyroid antibodies meet the criteria of subclinical hypothyroidism.

Secondary hyperthyroidism labs

TSH: high T4: high T3: high or normal

Subclinical hypothyroidism labs

TSH: high T4: normal T3 :normal

Primary hypothyroidism labs

TSH: high T4:low T3: low-normal

Primary hyperthyroidism labs

TSH: low T4: high or normal T3: high or normal

Subclinical hyperthyroidism labs

TSH: low T4: normal T3: normal

secondary hypothyroidism labs

TSH: low T4:low-nomral T3: low-normal

Following the surgical removal of the thyroid in thyroid carcinoma, which of the following proteins may be used as an indicator of cancerous regrowth of thyroid tissue?

Thyroglobulin (Tg)

What marker is important to measure in conjunction with determining thyroglobulin (Tg) levels with an immunoassay?

Thyroglobulin antibody (TgAb)

The American Thyroid Association (ATA) recommends the use of which laboratory test in screening all adults for thyroid disease, starting at age 35?

Thyroid-stimulating hormone (TSH)

Which of the following are considered among the classic symptoms of hyperthyroidism?

Weight loss or the inability to gain weight Bulging eyes Intolerance to heat and high temperatures

hormone tetraiodothyronine is formed (commonly called thyroxine or T4.)

When two DIT molecules combine through the action of TPO

C cells or parafollicular cells produce

a hormone called Calcitonin helps to regulate the metabolism of calcium and to maintain the integrity and density of the bones.

thyroglobulin

a protein possessing many tyrosine residues to which iodine molecules attach to form the thyroid hormones.

deiodinases

enzymes that convert T4 to T3 by removal of an iodine residue`

Humans usually have four parathyroid glands that are responsible

for regulating the calcium levels in circulation

thyroid produces and releases

hormones that regulate the metabolism of dietary sources of fats and carbohydrates, and help to regulate energy levels, body temperature, and to a lesser degree, play a role in fertility and bone health, heart rate & protein production.

subclinical hypothyroidism

in which the circulating levels of TSH are mildly elevated, but the thyroid hormones (eg, T3, T4) are still within the established reference intervals.

Which element is essential for the production of thyroid hormone?

iodine

Hyperplasia

is a term that most simply stated means overgrowth; of the thyroid may cause increased production of function T4 or T3 hormone, which may cause the classic symptoms of hyperthyroidism.

TRH, also known as thyrotropin-releasing factor

is secreted by the anterior region of the hypothalamus [determine if the pituitary gland is responsive to its stimulation in producing thyroid-stimulating hormone (TSH)]

Secondary hyperthyroidism

may be attributed to an over-stimulation of the thyroid. This may be due to increased production of TSH from the pituitary gland or TSH-secreting tumor, or more rarely from overproduction of TRH from the hypothalamus or thyrotropin-releasing hormone (TRH)-secreting tumor. (carcinoma, TSH-secreting tumors, TRH-secreting tumors)

Low thyroid levels in pregnant women may increase the risk of

miscarriage, premature delivery, anemia, postpartum hemorrhage, and pre-eclampsia, which is a condition that causes a significant rise in an expectant mother's blood pressure during the last three months of pregnancy.

What components are required to assemble thyroid hormones?

odine, thyroglobulin, tyrosine, and thyroperoxidase (TPO)

Following a complete removal of the thyroid gland due to an advanced malignancy, one must be concerned with the level of _____________ as the ___________________ may also be removed or damaged secondary to this surgical procedure.

parathyroid hormone (PTH) ; parathyroid glands

thyroid gland is under the direct control

pituitary gland and hypothalmus,

Primary hyperthyroidism

relates to the thyroid gland producing large amounts of hormone due to either uncontrolled growth of hormone-producing functional tissue or by way of an autoimmune process that interferes with the normal feedback control. (Thyroid nodules, thryoid adenoma, graves' disease, thryoiditis)

In cases where the entire thyroid gland is removed, the physician may use __________________________________ as a tumor marker to serve as evidence for cancer recurrence in a metastatic tumor.

thyroglobulin

The term "euthyroid" refers to a

thyroid gland that is functioning "true," producing adequate amounts of thyroid hormone in response to stimuli from the pituitary. ( WNL tests)

Thyroid-stimulating hormone (TSH), also called

thyrotropin, is a glycoprotein produced exclusively by the anterior pituitary gland

insufficient thyroid hormone production, or hypothyroidism symtoms/clinical features

will frequently present with an inability to lose weight, intolerance to cold temperatures, and chronically fatigued; decreased and inefficient metabolism, leading to obesity and high blood pressure. untreated can lead to cognitive impairment and depression.