Evaluation of the clonidine suppression test in the diagnosis of phaeochromocytoma

The aim of this study is to review the experience of the clonidine suppression test in a regional endocrine centre and to compare the diagnostic sensitivity and specificity using various previous published criteria. The design used is retrospective study. The subjects include 56 patients in whom clonidine suppression tests had been performed from 1995 to 2000: 15 with phaeochromocytoma and 41 patients in whom the diagnosis was excluded using a combination of biochemical testing, abdominal computed tomography scanning and clinical follow-up. Plasma catecholamines were measured by high pressure liquid chromatography on basal samples and at hourly intervals for 3 h after the administration of clonidine 300 μg orally and the following diagnostic criteria were applied: plasma noradrenaline+adrenaline>2.96 nmol l –1 at 3 h post-clonidine or a baseline plasma adrenaline plus noradrenaline>11.82 nmol l –1 ; plasma noradrenaline>2.96 nmol l –1 at 3 h post-clonidine and plasma noradrenaline>2.96 nmol l –1 and 2.96 mmol l –1 was used, sensitivity was 87% and specificity 95%. Using the former criteria, noradrenaline plus adrenaline>2.96 mmol l –1 , 1/15 in the phaeochromocytoma group had a normal result after clonidine suppression testing. Two of 41 in the non-phaeochromocytoma group had a false-positive result. Under carefully controlled conditions, the clonidine suppression test is well tolerated, safe and accurate for use in the investigation of patients with suspected phaeochromocytoma.