The clonidine suppression test (synonym: plasma catecholamines after clonidine) is a diagnostic test to detect autonomic catecholamine production, such as occurs in pheochromocytoma.
Principle: Clonidine is a centrally acting alpha-adrenergic agonist (stimulates presynaptic alpha-2 receptors in the CNS). This suppresses the release of catecholamines .
Procedure
Material needed
- 3.0 ml EGTA plasma, frozen, per blood draw for epinephrine, norepinephrine, dopamine
- 2.0 ml EDTA plasma per blood sample for metanephrines
Preparation of the patient
Note: Discontinue antihypertensive therapy (e.g., beta-blockers) at least 24 h before starting the test (except calcium antagonists for intolerable blood pressure -systolic > 180 mmHg, diastolic > 110 mmHg).
After 12 h of bed rest and fasting:
- Placement of a permanent cannula at least 30 min before the start of the test.
- Blood collection for basal level determination, label sample.
- Single oral administration of 0.3 mg clonidine (e.g., 1 tablet of Catapresan 300 µg).
- Further blood sampling after 60, 120, and 180 min.
Note: Patients with pheochromocytoma must have regular blood pressure and pulse rate measurements (every 30 min) before and after clonidine administration.
Confounding factors
- None known
Indications
- Suspected pheochromocytoma
Interpretation
- In healthy subjects, decreasing catecholamine concentrations are found after clonidine administration (suppression of catecholamine levels into the reference range or decrease to at least 50% of basal levels).
- A decrease in plasma metanephrine by <40% of basal value is highly suggestive of pheochromocytoma with high sensitivity and specificity.
Note: Multiple endocrine neoplasia type 2 must be considered when a pheochromocytoma is detected by clonidine suppression testing.