Adrenocorticotropic Hormone (ACTH)

Sample

1. The Patient’s plasma is needed.
   1. Place blood immediately in ice water and freeze plasma in 15 min.
2. The sample should be collected in a prechilled plastic test tube with EDTA or heparin.
3. Transfer the sample immediately to the lab on ice.
4. For the diagnosis of Cushing’s syndrome, the sample should be taken between 6 to 11 pm.
5. Centrifuge the sample at 4 °C and store at -20 °C immediately within 15 minutes of collection.

Precautions for Adrenocorticotropic Hormone (ACTH)

1. A stressful collection of blood will raise the level.
   1. Stress, mental or physical, and obesity can increase the value.
   2. Ask the patient to relax and reduce environmental stress.
2. Avoid physical activity 10 to 12 hours before taking the sample.
   1. Physical activity increases the value.
3. Ask the patient not to eat or drink after midnight on the night before samples are taken.
4. Stop medication like corticosteroids 48 hours before this test.
5. Collect the sample in a chilled plastic vial with EDTA or Heparin.
6. ACTH is very labile and requires antiprotease in the collecting vial.
7. In the routine, the ACTH level is not measured because it degrades in the plasma.
8. Put the patient on a low carbohydrate diet.
9. Oral contraceptives can decrease the value.
10. Glucocorticoids and estrogen decrease the value.
11. Blood glucose interferes with the accurate value.
12. A radioactive scan within one week of the test will interfere with accurate results.

Purpose of the test (Indications) for Adrenocorticotropic Hormone (ACTH)

1. This hormone is estimated in various conditions like Adrenal insufficiency, Cushing’s syndrome, and Acromegaly.
2. For the diagnosis of Addison’s disease (level is>1000 pg /ml).
3. Its level decreases in Secondary Adrenocortical Insufficiency, Adrenal carcinoma, and adenoma.
4. This is the test of the anterior pituitary gland.

Pathophysiology of Adrenocorticotropic Hormone (ACTH)

1. The anterior pituitary gland is considered the master gland due to many hormones secreted by this gland.
2. The hormones secreted are TSH (Thyrotropin), ACTH, reproductive hormones like FSH, LH, and many others.

The anterior pituitary lobe produces the following hormones:

Hormone	Chemical nature	Target organ	Main function
Follicle-stimulating hormone (FSH)	Glycoprotein (α and β chains)	Female = ovary Male = testes	Follicular growth and estradiol secretion Spermatogenesis
Luteinizing hormone (LH)	Glycoprotein (α and β chains)	Female  = ovary	Luteinization of the follicles With FSH leads to ovulation
Thyrotropin (TSH)	Glycoprotein (α and β chains)	Thyroid gland	Formation of thyroxine Secretion of thyroxine
Growth hormone (GH)	Protein and long-chain polypeptides	On whole body	Growth of bone Growth of muscles
Adrenocorticotropin (ACTH)	Protein and long-chain polypeptides	Adrenal cortex	Formation of cortisol Secretion of cortisol
Prolactin (PRL)	Protein and long-chain polypeptides	Breast	Growth of breast Stimulation of secretion of milk

3. Functions of the hormones:
   1. These hormones maintain a constant internal environment in the body fluid which will lead to homeostasis.
   2. It will regulate the growth and development of the body as a whole.
   3. It will regulate energy production and stabilizes the metabolic rate (system).
   4. It will help the body to adjust to a stressful or emergency state.
   5. It will promote sexual maturation, maintain the sexual rhythm and help the reproductive process.
4. Hormones that are soluble in plasma are from:
   1. Hypothalamus.
   2. Anterior and posterior pituitary.
   3. Pancreas.
   4. Parathyroid.
5. Hormones that are poorly soluble in plasma and will need plasma proteins as a carrier is from:
   1. Adrenal cortex.
   2. Gonads.
   3. Thyroid.
6. Pituitary glands consist of:
   1. Anterior lobe (adenohypophysis).
   2. Posterior lobe (neurohypophysis).
7. The anterior pituitary lobe produces adrenocorticotropin hormone (ACTH).
   1. ACTH is a 39 amino acid peptide hormone secreted by the anterior pituitary gland.
   2. The anterior hormones are produced in a pulsatile pattern.
      1. Basal level = close to 5 pg/mL.
      2. Highest level = 6 to 8 A.M.
      3. Lowest level = 6 to 11 P.M.
      4. The plasma level of ACTH does not exceed 50 pg/mL.
   3. Anterior pituitary hormones are either tropic means their action is specific for another endocrine gland, or are direct effectors because they act directly on the peripheral tissue.
      

      Adrenocorticotropic Hormone: ACTH formation and the anterior pituitary glands

2. Corticotropin-releasing hormone (CRH) is made and released from the hypothalamus and gives rise to ACTH release from the pituitary glands.
   1. CRH stimulates ACTH production in the anterior pituitary gland.
   2. Now ACTH sends signals to the adrenal gland (cortex), which secretes steroids (cortisol, androgen, and aldosterone).
   3. The rising level of cortisol acts as a negative feedback mechanism and stops CRH and ACTH production.
      

      Hypothalamus, CRH, and ACTH cycle

      

      ACTH effect on the adrenal gland

3. There are two peaks:
   1. ACTH is released in a burst, so its level can vary from minute to minute
      1. 1. Highest between 6 to 8 AM.
         2. The lowest level between 9 to 10 (6 to 11) PM.
         3. During sleep is the normal level.
            

            ACTH level during 24 hours

4. Pregnancy, menstrual cycle, and stress increase secretion.
   1. ACTH is released in response to many stresses.
5. ACTH is advised for investigating disorders of the hypothalamic, pituitary, and renal system.
6. ACTH is secreted by the anterior pituitary gland that signals the adrenal gland to produce steroids (androgens, cortisol, and aldosterone). These are needed for the normal functioning of the body.
7. With adrenal insufficiency, the pituitary gland release proopiomelanocortin, and ACTH are increased.
8. ACTH is unstable in the blood. Most commercial RIA kits are insensitive and nonspecific to measure ACTH.

Normal ACTH

Source 2

• 6 to 8 a.m = < 80 pg / mL or <18 pmol /L (SI units).
• 6 to 11 p.m = < 50 pg /mL or <11 pmol /L (SI units).
• or less than 120 pg/ml

Another reference gives the following values:

• 8 AM ( unrestricted activity) = <120 pg/mL
• 4 to 8 PM <85 pg/mL
• Cord blood   = 50 to 570 pg/mL
• Newborn      =  10 to 185 pg/mL

Another reference gives the following values:

Adults, Adolescent, child, and elders

• 8 A.M. fasting = 15 to 100 pg/mL (10 to 80 ng/L)
• 4 P.M. nonfasting = 10 to 50 pg/mL (10 to 50 ng/L)
• Newborn = 10 to 185 pg/mL

Cushing’s Syndrome

1. Cushing’s syndrome is named after the name of Dr. Harvey Cushing, who was the surgeon.
2. Causes of Cushing’s syndrome:
   1. As a result of treatment with corticosteroids, this is the nonadrenal cause.
   2. Secondary to a benign hormone-secreting pituitary adenoma. These are ACTH secreting adenomas (68%).
      1. Cortisol production from the adrenal tumors or nodules (17%).
      2. Excess ACTH ectopic production (15%). Mostly there are malignant tumors.
   3. Chronic alcoholism, stress, and obesity.
3. Clinical presentation:
   1. This may be a form of Hyperadrenalism or Hypercortisolism with common clinical presentations.
   2. These patients have similarities like diabetes mellitus  type1 (insulin resistance).
   3. There are 4 times increased mortality even after successful treatment.
   4. Patients have cardiovascular diseases. There is left ventricular hypertrophy.
      1. There are changes in the ECG and nocturnal hypotension.
      2. Blood pressure changes were seen in 85 to 90%.
      3. Central obesity is seen in 90%.
      4. Glucose intolerance is seen in 80%.
      5. Hirsutism is seen in 65%.
      6. There are abnormal menses by 60%.
      7. There may be muscle weakness in 60%.
   5. Untreated cases have a 50% mortality for 5 years.
      

      Cushing’s syndrome, signs, and symptoms

4. Diagnosis:
   1. The abnormal Overnight Dexamethasone suppression test and 24 hours urinary cortisol test are diagnostic of Cushing’s Syndrome.
   2. Free urinary cortisol level (24 hours sample) is most sensitive,  95 to 100% and specificity of 98%.
      1. Random plasma cortisol level is of little value for the diagnosis of Cushing’s syndrome.
      2. There is a loss of diurnal rhythm because late-night values remain high.
         1. The ideal time for the collection of ACTH and cortisol is between 11.00 p.m and 12.00 a.m.
         2. A single midnight serum sample concentration >7.5 µg/dL is diagnostic of Cushing’s syndrome with a sensitivity of 90 to 96% and specificity of 100%.
      3. Saliva cortisol level at 11.00 p.m, when combined with 8.00 a.m, salivary cortisol concentration after the 1 mg overnight dexamethasone suppression test had sensitivity and specificity of 100%.
   3. Radiological work-up:
      1. Adrenal gland CT distinguishes hyperplasia vs. tumor.
      2. Adrenal MRI distinguishes the carcinoma.
      3. Pituitary CT diagnoses 85% of the microadenoma.
      4. CT scan finds ectopic ACTH source like bronchial adenoma, medullary thyroid carcinoma, and squamous cell carcinoma.
   4. When Cushing’s syndrome is due to a Pituitary or ectopic source, then the ACTH level is high.
   5. When the source is the Adrenal gland, the ACTH is low.

Table for differentiation of Cushing’s syndrome and Addison’s disease:

Disease	ACTH value	Cortisol value
Cushing’s syndrome	Increased/low	Increased
Adrenal adenoma	Low	Raised
Adrenal cancer	low	Raised
ACTH- producing Pituitary tumor	Raised	Raised
Ectopic ACTH (Lung cancer)	Raised	Raised
Addison disease
Adrenal gland failure ( Infarction, Haemorrhage)	Raised	Low
Congenital adrenal hyperplasia	Raised	Low
Hypopituitarism	Low	Low

Increased ACTH level is seen in:

1. Addison disease (primary adrenal insufficiency).
2. Ectopic ACTH syndrome.
3. Cushing’s syndrome. This is dependent upon the adrenal hyperplasia due to the pituitary gland.
4. Stress.

Decreased ACTH level is seen in:

1. Hypopituitarism.
2. Secondary adrenal insufficiency is due to pituitary insufficiency.
3. Adrenal adenoma or cancer.
4. Exogenous steroid administration.

Test value for the Layman:

1. This test is advised if the patient has diabetes mellitus, reduced glucose tolerance, and muscle wasting to rule out Cushing syndrome.
2. If there are truncal obesity and thin extremity.
3. In case of abnormal lipid metabolism.

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