Growth Hormone (GH) , Somatotropin Hormone

Sample
- This test is done on serum (clotted blood 3-5ml).
- A serum sample is preferred.
- Plasma (EDTA) has lower values with some methods.
- The patient should be fasting and complete rest for at least 30 minutes before taking the blood.
- It is stable for 8 hours at 2 to 8 °C.
- It can be kept for a longer period at -20 °C.
Precautions
- Perform the test immediately because the half-life of GH is 20 to 25 minutes.
- Immediately refrigerate the serum.
- The patient should be fasting after midnight.
- The patient must be fasting and at complete rest, 30 min before the sample is taken because this may increase the level.
- Avoid stress, low blood glucose, and exercise during the sample collection.
- EDTA plasma gives lower values.
- Random measurement is not useful because of episodic variation in the GH level.
- Drugs that may increase the level are Amphetamine, Estrogen, Dopamine, Insulin, Methyldopa, Levodopa, Histamine, and Nicotinic acid.
- There are certain drugs that decrease the GH level are Phenothiazine and Corticosteroids.
Purpose of the test (Indications)
- Growth hormone is done to identify its deficiency in:
- Adults with short stature.
- Delayed sexual maturity.
- or other growth abnormalities.
- To diagnose gigantism or acromegaly,
- This can be used to identify the pituitary hypofunction or hyperfunction.
Various type of tests:
- A growth stimulation test can be done to evaluate the deficiency.
- Growth suppression test is done in the gigantism and acromegaly in adults.
- Oral glucose tolerance test is very helpful where there is a rise in glucose level. Normally GH is suppressed. But in acromegalic patients, there is slight or no decrease in GH.
- Give glucose 75 to 100 grams in 5 minutes, then get the sample for GH at 30, 60, 90, and 120 minutes.
Pathophysiology
- The growth hormone is a single-chain polypeptide with a molecular weight of 21,500Da and contains 191 amino acids.
- This is one of the hormones involved in growth produced by the pituitary gland.
- This is also called as Somatotropin, is secreted by acidophilic cells of anterior pituitary glands.
- It is stored in the cells as granules.
- Growth hormone production is pulsatile.
- GH plays a role in the growth from birth until the end of puberty.
- GH promotes protein synthesis and stimulates skeletal growth.
- GH releasing hormone (GH-RH) is under the control by the hypothalamus which acts on anterior pituitary glands, and it releases GH.
- Another inhibitory hormone, Smatotropin-release-inhibitory factor (SRIF) is produced from the hypothalamus and it has the inhibitory action on the pituitary gland.
- GH secretion is increased by various factors.
- GH action: Hypoglycemia stimulates the pituitary gland to secrete GH. It is an antagonist to insulin. This was used as a stimulation test but not safe.
- Arginine is used which activates the secretion of GH.
- GH increases glucose by:
- inhibiting the entry of glucose into the muscle cells.
- By inhibiting glycolysis.
- By inhibiting the formation of triglycerides from the glucose.
- GH affects many tissues through a group of peptides (Somatomedins).
- Increased level of Somatomedins leads to an increase in the production of Somatostatin which is released from the hypothalamus.
- GH is released (level increases):
- During sleep a slight rise in early sleep.
- Peak level in the deep sleep.
- Around 11 pm or midnight.
- exercise.
- Ingestion of protein.
- In hypoglycemia.
- Spike occurs after 3 hours of the meals or exercise.
- Spike occurs after 90 minutes of sleep. The peak is during deep sleep.
- The level is low during the day and is around 5 ng/mL.
- GH has diurnal variation in level.
- During sleep a slight rise in early sleep.
- GH insufficient amount leads to:
- limited growth.
- Dwarfism.
- Delay in maturity.
- GH overproduction leads to :
- .Gigantism.
- Acromegaly. (Increase in bone thickness and width).
- GH has diurnal variation in the concentration.
- The secretion of GH is episodic and variable, sometimes the level may reach 40 ng/ml in a healthy subject.
- The highest values are noted during the deepest sleep level. So it’s level is increased during sleep.
- So the best time is 60 to 90 minutes after the deep sleep.
- Or do the exercise for 30 min and get the sample for GH, which will be at the highest level.
- The GH may increase ten times than the normal level during sleep.
- This test may be used to monitor the acromegaly treatment.
- Obesity reduces the release of GH and response to insulin.
- Hypoglycemia stimulates the pituitary to secretes GH.
- The ability to secrete GH to conventional challenges decreases with age.
- Growth hormone functions:
- It promotes protein synthesis.
- It stimulates skeletal growth.
- Its deficiency leads to dwarfism.
- Its excess leads to gigantism.
Clinical presentation of growth hormone (GH) excess:
- Excess GH is seen in the eosinophilic or chromophobe adenomas of the pituitary gland.
- 75% of these tumors can be diagnosed on CT scan.
- The excess of GH is called Acromegaly.
- When seen before the long bone growth is complete then it is called Pituitary gigantism.
- This can be diagnosed with the physical appearance of the patient.
- There is an overgrowth of the soft tissue and bone.
- There is coarse oily skin.
- There is a large tongue.
- There are prominent supraorbital ridges.
- The teeth spacing is increased.
- Hands are thick spade-like.
- The patient will have arthralgia and kyphosis.
- Voice is coarse.
- The patient may develop proximal muscle weakness.
- Sweating and headache are common.
- The patient will have progressive heart failure.
- The reversibility of the physical changes depends upon the duration of the disease.
- Acromegaly may lead to severe disability or death due to cardiac or neurological complications.
- There is an abnormal response of GH to oral glucose administration.
- The normal person shows <1 ng/ mL of GH after an oral dose of glucose.
- Complications are:
- The patient may develop diabetes mellitus.
- The patient will have hypertension and cardiomegaly.
- There is obstructive sleep apnea.
- Diagnosis:
- Advise the glucose tolerance test and collect a blood sample at 0, 30 min, 60 min, 90 min.
- Estimate both glucose and GH.
- The values will be suppressed around <1.0 ng/mL.
- Another test is IGF-1 (insulin-like growth factor 1) where its concentration increases in acromegaly.
- Advise the glucose tolerance test and collect a blood sample at 0, 30 min, 60 min, 90 min.
Clinical presentation of deficiency of growth hormone:
- This is usually seen in the hypothalamic and pituitary tumors.
- Growth is a dwarf and short stature children.
- Diagnosis:
- Advice Two stimulating tests like insulin hypoglycemia or arginine.
- Measure GH at 30, 60, 90 minutes.
- Normal patients show an increase of >8.0 ng/mL.
Normal
Source 1
Age | ng/mL |
Cord blood | 8 to 41 |
Newborn | |
One day | 5 to 53 |
One week | 5 to 27 |
Child 1 to 12 months | 2 to 10 |
Adult | |
Male | 0 to 4 |
Female | 0 to 18 |
> 60 years | |
Male | 1 to 9 |
Female | 1 to 16 |
- To convert into SI units x 1.0 = µg/L
Source 2
Men | <5 ng/mL or <5 µg/L) |
Women | <10 ng/mL or <10µg/L) |
Newborn | 10 to 40 ng /ml |
Child | 0 to 10 ng/ml |
- The random level of GH provides little diagnostic information.
- The single estimation may not be helpful because of the variation in the level of GH during the day.
The increased GH level is seen in:
- Pituitary gigantism (Acromegaly = up to 400 ng/ml).
- Ectopic GH secretion e.g. Stomach neoplasm, lung.
- Renal failure.
- Cirrhosis.
- Stress, exercise, prolonged fasting.
- Uncontrolled diabetes mellitus.
- Anorexia nervosa.
- Starvation and malnutrition.
- Hypoglycemia.
- Major surgery.
- Exercise.
The decreased GH level is seen in:
- Pituitary dwarfism, hypopituitarism.
- Adrenocortical hyperfunction.
- Hyperglycemia.
- Delayed sexual maturity.
- Growth hormone deficiency.
Treatment
- For the acromegaly due to adenoma is transsphenoidal resection of the tumor.
- Another method is gamma knife multiport irradiation.
- Somatostatin (SST) long-acting needs only one dose per month.