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Growth hormone suppression test - Investigation protocol

Indication

Diagnosis and monitoring of patients with suspected acromegaly.

Preparation

Glucose solution is best prepared in advance as glucose dissolves better in warm water but is more palatable when cold. On the day prior to the test, dissolve 75 grams of anhydrous glucose (82.5 grams of glucose monohydrate, obtainable pre-weighed from pharmacy) in warm water and store in a fridge overnight.

The patient must be fasted from midnight (sips of water only). However, medications should continue as normal unless otherwise instructed by the consultant.

Procedure

Insert an indwelling cannula gauge 20 with a three-way tap. Using the vacutainer connector system or a syringe, fill one plain clotted bottle for growth hormone, and one fluoride oxalate bottle for glucose. Label with patient identification and label the tubes -10minutes.

Flush the cannula with 2mls 0.9% sodium chloride after each blood sample; withdraw 2mls blood and discard to remove any trace of the sodium chloride flush prior to taking each sample.

Allow the patient to rest for 10 minutes before taking further samples into a further plain clotted bottle and a fluoride oxalate bottle. Label both with patient identification, date and time=0 minutes.

Give the glucose solution to drink (within 10 minutes). Some patients may feel sick and have vaso-vagal symptoms during this test. It is therefore advisable that they be on a couch or bed during the test where they may rest and elevate legs should this occur. 

Collect further blood samples as above for growth hormone and glucose, every 30 minutes for 2.5 hours, making sure that each sample is clearly labelled with the patient identification, date and time of sample (i.e. 30, 60, 90, 120,150 minutes). Remove cannula.

The patient may then have a meal and go home.

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