From the Guidelines
A positive catecholamine plasma test is typically indicated by elevated levels of plasma free metanephrines, with very high values being diagnostic for phaeochromocytoma, as stated in the 2007 guidelines for the management of arterial hypertension 1. The diagnosis of phaeochromocytoma is based on establishing an increase in plasma or urinary catecholamines or their metabolites.
- The test that achieves the highest sensitivity (97 – 98%) is the measurement of plasma free metanephrines, together with urinary fractionated metanephrines 1.
- Measurement of urinary fractionated metanephrines remains the diagnostic test of choice, as measurement of plasma free metanephrines is not available for routine diagnosis 1.
- Very high values of plasma or urine catecholamines require no further testing, while modestly elevated values may necessitate stimulation or suppression tests with glucagon or clonidine, respectively 1. The interpretation of catecholamine plasma test results must consider the clinical context and potential interfering factors, such as stress, physical activity, and certain medications.
- The clonidine suppression test is regarded as negative when there is a marked reduction of plasma catecholamines 1.
- The glucagon test must be performed after the patient has been effectively treated with an a-adrenoreceptor antagonist to prevent marked blood pressure increases after injection of the hormone 1.
From the Research
Catecholamine Plasma Test
- The catecholamine plasma test is used to diagnose pheochromocytomas, which are rare, mostly benign catecholamine-producing tumors of chromaffin cells of the adrenal medulla or of a paraganglion 2.
- A positive test result is typically indicated by elevated levels of catecholamines, such as epinephrine and norepinephrine, in the plasma 2.
- The diagnosis of pheochromocytomas depends mainly upon the demonstration of catecholamine excess by 24-h urinary catecholamines and metanephrines or plasma metanephrines 2.
Interpretation of Test Results
- Elevated plasma metanephrines are a sensitive indicator of pheochromocytoma, and a positive test result can confirm the diagnosis 2.
- However, the test results should be interpreted in conjunction with clinical manifestations, such as sustained or paroxysmal hypertension, severe headaches, palpitations, and sweating, which are typical of pheochromocytomas 2.
- Other studies have focused on the medical management of pheochromocytoma, including the use of alpha-adrenergic blocking agents, beta-adrenergic receptor blockade, and other pharmacologic agents 3, 4, 5, but do not provide specific information on the interpretation of catecholamine plasma test results.