Clonidine Suppression (3-Hour)
Clonidine Suppression Test (Three-hour)
Diagnose pheochromocytoma and those paragangliomas that may secrete epinephrine, norepinephrine, or both. Such tumors may cause paroxysmal or persistent hypertension. Investigation of hypertensive patients, especially younger individuals, particularly when hypertension is paroxysmal, suggesting pheochromocytoma.
Several medications have been shown to prevent clonidine suppression, thus rendering false-positive results. These include β-adrenergic blockers, tricyclic antidepressants, and thiazide diuretics. If possible, these drugs should be discontinued 48 hours before collection. The α-adrenergic blocking agents do not interfere with clonidine suppression. Several definitions of a normal plasma catecholamine response to clonidine have been postulated:
• A minimum plasma norepinephrine level ≤500 pg/mL
• ≥50% norepinephrine decline from baseline and a norepinephrine level ≤500 pg/mL
• A minimum plasma total catecholamine (norepinephrine+epinephrine) concentration ≤500 pg/mL
Sjoberg et al have concluded that minimal suppression occurs two to three hours after clonidine administration with the greatest diagnostic accuracy (92%) obtained when the normal response is defined as a level of total plasma catecholamine ≤500 pg/mL. Taylor et al have demonstrated an increase in false-positive results by using the 50% reduction criteria. This is especially true if the baseline results are within the established reference interval.
One tube (3 mL) each for baseline specimen, two-hour specimen, and three-hour specimen
One tube (2.2 mL) each for baseline specimen, two-hour specimen, and three-hour specimen
Chilled lavender-top (EDTA) tube
The patient should fast overnight and abstain from smoking. Walnuts, bananas, and interfering medications should be avoided for a week prior to specimen collection. An indwelling heparinized catheter is recommended, as venipuncture can cause an increase in the substances for which testing is being performed. The patient should remain recumbent during the entire collection procedure. Thirty minutes after the insertion of the indwelling catheter, blood is drawn for the baseline catecholamine determination. Clonidine hydrochloride (0.3 mg) is given orally, and repeat specimens for plasma catecholamines are collected two and three hours later.
Draw blood in chilled lavender-top (EDTA) tube. Invert tube to allow preservatives to mix thoroughly. Centrifuge at 4°C (chill carriers if a refrigerated centrifuge is unavailable). Transfer plasma to labeled plastic transport tubes. Freeze immediately at -20°C and ship frozen. “Baseline,” “two-hour,” and “three-hour” should be prelabeled on the transport tubes. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Specimen not drawn in correct tube; plasma not received frozen; thawed specimen; inadequate patient preparation
Return Back to Test Directory
Providing top patient care with fast results.
7018 South Utica Avenue
Tulsa, Oklahoma 74136