Thyroid-stimulating hormone (TSH)

What sample is needed for Thyroid-stimulating hormone (TSH)?

• Venous blood is taken, and the test is done on the patient’s serum.

What are the indications for Thyroid-Stimulating Hormone (TSH)?

1. TSH differentiates Hypothyroidism from hyperthyroidism.
2. TSH is used to diagnose primary hypothyroidism.
3. TSH is used to differentiate primary from secondary hypothyroidism.
4. TSH also differentiates hypothyroidism due to the hypothalamus (Tertiary hypothyroidism).
5. TSH level is also done for suppressive or replacement therapy.
6. TSH has also been done in a newborn with primary hypothyroidism with a low T4 level.

How will you define thyroid-stimulating hormone (TSH)?

1. The anterior pituitary gland produces TSH.
2. TSH plays an important role in regulating the thyroid glands’ activity, which produces important hormones for the body.
3. TSH controls the metabolism, growth, and development of the body.

What is the structure of Thyroid-Stimulating Hormone (TSH)?

1. TSH is a glycoprotein hormone composed of two polypeptide chains, alpha and beta.
   1. Alpha (α) subunit consists of 92 amino acids.
   2. The beta (β) subunit consists of 118 amino acids, and the biological activity is because of the Beta subunit.
   3. TSH molecular weight is 28,000 Da.

2. It arises from the prehormone and prohormone.
3. It has a short half-life of minutes to a few hours compared to other hormones like steroids.
4. TSH binds with the specific receptors for TSH found in the cytoplasmic membrane of the thyroid cells.
5. It releases the second messenger that activates cAMP and protein kinase and stimulates further biochemical reactions.
6. TSH is transported free and not bound to protein carriers in the body fluids.
7. With other adrenergic neuropeptides, TSH binds to the cytoplasm membrane receptors, and the thyroid gland secretes the T4 and T3.
8. The thyroid gland has large hormone stores and a slow normal turnover rate.

What is the role of TSH?

1. The pituitary gland produces TSH, which stimulates the thyroid gland to distribute stored hormones.
2. TSH stimulates the secretion of T4 and T3.
   1. TSH secretion is regulated by T4 and T3 feedback inhibition.
   2. Low levels of T3 and T4  are stimuli for TSH and TRH.

What are the interpretations of TSH?

1. Thyrotropin-releasing hormone (TRH) from the hypothalamus regulates TSH stimulation.
   1. TSH is the single most common test for primary hypothyroidism.
2. In the damaged Pituitary and hypothalamus, TSH and TRH are low or zero in spite of low T3 and T4.
3. If there is clear evidence of hypothyroidism and TSH is normal, then think about the possibility of hypopituitarism.
   1. TSH level is high in primary hypothyroidism.
   2. TSH levels are low in hyperthyroidism.

3. Thyroid disorder = T4 decreased + TSH normal or raised
4. Pituitary disorder = T4 decreased + TSH decreased

What is the normal TSH level?

Source 1

• To converts into SI unit x 1.0 = mU/L

Source 2

• Adult = 0.4 to 5.6 mIU/L
• Newborn = 3 to 20 mIU/L
• Cord blood = 3 to 12 µU/mL
  • Values vary between laboratories.

Another source

• Adult
• 21 to 54 years = 0.4 to 4.2 mU/L
• 55 to 87 years = 0.5 to 8.9 mU/L
• Newborn = 1.7  to 9.1 mU/L
  • 0.3 to 3.04 mIU/L  (another reference)
• Pregnancy
  • First trimester = 0.3 to 4.5 mU/L
  • Second trimester = 0.5 to 4.6 mU/L
  • Third trimester = 0.8 to 5.2 mU/L

(Normal values vary from lab to lab and different methodologies)

• Adult = 0.4 to 4.2  µIU/L ( SI units are the same )
• Neonates = 3 to 20  µIU/L

What are the causes of increased TSH levels?

1. Adults and neonates with primary hypothyroidism.
   1. Congenital Cretinism.
2. Hashimoto’s thyroiditis.
3. The hypothyroid patient received inadequate treatment.
4. Thyrotoxicosis due to pituitary tumors.
5. Thyrotropin-producing tumors, e.g., ectopic TSH produced by lung and breast cancers
6. TSH antibodies.
7. Large doses of iodine.
8. Chronic and severe illness.

What are the causes of decreased TSH levels?

1. Primary Hyperthyroidism.
2. Secondary and tertiary hypothyroidism.
3. Overtreatment in a hypothyroid patient.
4. Treated Grave’s disease patient.

What is the picture of thyroid hormones in various diseases?

Graves disease

How will you define Graves disease?

1. Graves’ disease is an autoimmune disorder that primarily affects the thyroid glands, leading to hyperthyroidism.
2. There is an overproduction of thyroid hormones.

What is the mechanism of Graves’ disease?

1. It is one of the most common causes of hyperthyroidism.
2. The immune system produces antibodies that stimulate the thyroid gland.
3. These antibodies are called thyroid-stimulating immunoglobulins.
4. What are the risk factors:
   1. If there is a family history of autoimmune diseases.
   2. It is more common in females.
   3. Smoking is a risk factor and leads to ophthalmopathy.
   4. If there is stress or emotional trauma.
5. It causes the increased size of the thyroid gland.
6. It increases the amount of hormones.

What will be the clinical presentation?

1. There is an increase in the size of the thyroid gland (Goiter).
2. There is weight loss even with increased appetite.
3. Heartbeats are irregular, leading to tachycardia or arrhythmias.
4. There is nervousness, irritability, and anxiety.
5. There is heat intolerance and sweating.
6. There are tremors of hands or fingers.
7. The patient may have weakness or fatigue.
8. These patients typically have exophthalmos.
   1. The eyes are dry and irritable.
   2. These patients’ eyes may be red.
   3. These patients have sensitivity to light.
9. These patients may have overall vision problems.
10. These patients’ skin is red or swollen, called graves’ dermopathy.

How will you diagnose Graves’ disease?

1. There is a high level of T4 and T3.
2. There is a decreased level of TSH.
3. There is the presence of antibodies (thyroid-stimulating antibodies).
4. Check the eyes for the Graves’ ophthalmopathy.
5. Advise Ultrasonography for goiter.
6. Advise radio-iodine uptake to assess the thyroid function.
   1.  TSH is decreased.
   2.  Free T4 is increased.

How will you differentiate different thyroid diseases?

Questions and answers:

• Note, please see more details on the thyroid function test.