CLONIDINE STIMULATION TEST FOR GROWTH HORMONE
INTRODUCTION
This test is indicated in suspected Grown Hormone (GH) deficiency and is safer than insulin-induced hypoglycaemia, especially in children. Clonidine stimulates GH release from the anterior pituitary and causes elevation of serum GH levels. Thyrotrophin Releasing Hormone (TRH) can be administered with clonidine to provide a further test assessing anterior pituitary reserve.
PRECAUTIONS
Please refer to the Trust’s phlebotomy procedure for sample
collection precautions.
Caution: Drowsiness and hypotension may be side effects and
blood pressure should be monitored at 30 minute intervals throughout the test and for 3
hours afterwards. Hypotension can usually be relieved by raising the foot of the bed.
PATIENT PREPARATION
Patient should be fasted for at least 8 hours before commencing test. The patient should be comfortable, recumbent in bed and at complete physical and mental rest throughout the test. After the test, because of the risk of hypotension, continuing bed rest for 3 hours is essential.
Clonidine dosage: |
Clonidine is administered orally as 25ug DIXARIT tablets (Boehringer Ingelheim) in a dose of 100ug/m2 of body surface area and rounded up to the nearest whole number of tablets. |
PROTOCOL
After OVERNIGHT FAST
1. |
Insert indwelling intravenous cannula and wait at least 30 mins. |
2. |
Take basal blood sample (minimum 5ml blood in SST tube – yellow top) |
3. |
Give appropriate dose of Clonidine orally and optionally 200ug of TRH intravenously as a single bolus – NOTE TIME. |
4. |
Take further blood samples (minimum 5ml blood in SST tube – yellow top) at 20, 60, 90, 120 and 150 minutes after Clonidine/TRH has been given. NOTE ACTUAL TIMES ON COLLECTION TUBE |
Label all samples with sequence number and actual time taken. When test is complete send request form and samples to Clinical Biochemistry as soon as possible (keep at 4°C until delivered).
INTERPRETATION
Normal Response: There is a steep rise of serum GH from <10 mU/l initially to >20 mU/l at 60 – 120 mins after Clonidine administration.
An inadequate response is seen in GH deficiency, either as an isolate state, or as part of panhypopituitarism; a poor response may also occur in primary hypothyroidism. In some children, social deprivation also leads to a poor response.
Reviewed by: Tony
Everitt, Consultant Biochemist
Last edited 07/08/08