Typically, growth hormone injection testing is used to identify GH deficiency in the body, as well as assessing pituitary gland condition. Furthermore, it can detect when there’s excess somatropin in the body, and is also used to diagnose and examine the treatment of gigantism and acromegaly. The procedure is usually done as a follow-up to other pituitary hormone test results.
Nevertheless, since growth hormone is naturally released in pulses by the pituitary gland, a single blood-level measurement may not be enough to make any clinical diagnosis. Therefore, most experts prefer testing for suppression or stimulation of the substance instead since these have more meaningful results.
I. GH Stimulation Tests
They help to diagnose somatropin deficiency and hypopituitarism. For the initial stimulation test, a blood sample is taken after the person has fasted for about 10-12hrs. Thereafter, under close supervision by a physician they would be given an injection that will normally stimulate the release of growth hormone from pituitary gland.
Next, blood samples would be taken at specific time intervals and somatropin levels tested in each stage to determine whether the pituitary gland was triggered to release the expected amounts of GH. For this process, the most commonly applied stimulant is arginine, though others that may also be used are glucagon and clonidine. Additionally, since regular exercise can cause a shift in GH levels, it can also be used as a stimulant for the release of this hormone.
To assess whether the injection has worked, the physician will determine whether insulin-like growth factor-1 (IGF-1) has been produced by the body. This hormone is responsible for mediating the effects of GH, as well as promoting normal tissue and bone growth and development. Nevertheless, unlike growth-hormone its level is usually stable throughout the day in the bloodstream. This ultimately makes IGF-1 a great indicator of average GH amounts, plus IGF-1 testing can further be used to help assess hormone deficiency and excess.
II. GH Suppression Tests
This procedure is used to diagnose excess of the compound. First, a blood sample is drawn from the individual after 10-12hrs of fasting. Then the individual is given a normal glucose solution of about 100gms to drink. Next, blood samples are taken at timed periods and tested for GH. This will help determine if the pituitary-gland has been adequately suppressed by the glucose dosage or not.
Furthermore, GH suppression test can also be used to assess treatment of the GH-producing pituitary tumor. If a growth is detected, growth hormone levels can be measured immediately after the tumor has been removed, so as to find out whether the entire growth was successfully removed or some parts remained inside the body. In this process, tests may be conducted at regular intervals for some years later in order to assess GH production, and also detect tumor recurrence if possible.
Apart from the above procedures, other blood-tests that can also be used to assess the effect of growth hormone injection and pituitary gland function are prolactin, cortisol, testosterone, cortisol and TSH amongst others. These tests are usually carried out before the GH testing, so as to ensure that basic testing parameters are normal.