Clonidine suppression test reliably differentiates phaeochromocytoma from essential hypertension

1. Clonidine resulted in significant suppression of both noradrenaline (NA) and adrenaline (ADR) in essential hypertensives (EHT) without any false positive findings. That is, every patient who failed to suppress had phaeochromocytoma (PH). 2. The clonidine suppression test (CST) produced minimal suppression of NA in NA-secreting PH (NA-PH) and correctly identified two NA-PH with normal basal plasma NA. 3. In ADR-secreting PH (ADR-PH) the CST did not result in significant suppression of ADR levels, whether elevated or normal basally. 4. The CST proved to be an accurate discriminator of PH from other forms of hypertension.