Baseline levels of GH are affected by many factors and may be misleading at times. Stimulation tests are performed to determine responsiveness to substances that normally stimulate GH secretion, such as arginine and L-dopa. Insulin also may be given to induce hypoglycemia, which in turn stimulates GH secretion. It has been found that blood sugar levels of less than 50 mg/dL cause GH levels to rise 10 times or more in normal individuals. Idiosyncratic responses to the different stimulants may occur. Thus, it may be necessary to perform two or three different stimulation tests before arriving at diagnostic conclusions.⁴⁰

• Factors that may affect serum GH determinations also may alter results of GH stimulation tests.

• Low or undetectable serum GH levels, with GH deficiency or adult panhypopituitarism confirmed by no increase after administration of the stimulant
• Confirmation of the diagnosis of acromegaly as evidenced by reduced GH output after L-dopa is administered as a stimulant (i.e., an idiosyncratic response is seen in acromegaly)

Nursing Alert

• If insulin is used as the stimulant, the client should be observed carefully during and after the test for signs and symptoms of extreme hypoglycemia.

Nursing Care Before the Procedure

Initial client preparation is the same as that for serum GH determinations.

• The client should be weighed on the day of the test because dosage of the stimulant is determined by weight.
• Because several blood samples will be obtained and because certain of the stimulants (i.e., insulin and arginine) are administered IV, the client should be informed that an intermittent venous access device (e.g., heparin lock) will be inserted.

An intermittent venous access device is inserted, usually at about 8 AM, and a venous sample is obtained and placed in a red-topped tube. The sample is handled gently to avoid hemolysis and sent to the laboratory immediately.

The stimulant is then administered. L-Dopa is administered orally; arginine and insulin are administered IV in a saline infusion. If insulin is used to lower blood sugar, an ampule of 50 percent glucose should be on hand in the event that severe hypoglycemia occurs.

After the stimulant is administered, three blood samples are obtained via the venous access device at 30-minute intervals. The samples are placed in red-topped tubes and sent to the laboratory immediately upon collection.

Nursing Care After the Procedure

Care and assessment after the procedure are essentially the same as for serum GH determinations.

• If an intermittent venous access device was inserted for the procedure, remove after completion of the test and apply a pressure bandage to the site.
• If insulin was used as the stimulant, resume dietary intake as soon as possible after the test is completed and observe for signs of hypoglycemia.
• Complications and precautions: If insulin is used, note and report signs and symptoms of hypoglycemia such as sweating, tachycardia, tremors, irritability, or confusion. Prepare client for IV glucose administration.