Biochemical screening to detect overproduction of catecholamines (epinephrine, norepinephrine) should be performed in patients with:
- New-onset refractory hypertension (hypertension that does not respond to medical therapy).
- Paradoxical blood pressure response during anesthesia or surgical procedures.
- Hereditary (congenital) predisposition regarding a pheochromocytoma.
- Sudden panic attacks
- As well as in asymptomatic patients with incidentaloma (accidentally discovered neoplasms) of the adrenal glands.
Note: Two weeks before laboratory diagnostics should be discontinued interfering drugs, which include sympathomimetics (drugs that affect the sympathetic nervous system), alpha blockers, antidepressants, clonidine.Do not necessarily discontinue diuretics (draining agents), calcium antagonists, ACE inhibitors and sartans.
1st-order laboratory parameters-obligatory laboratory tests.
- Determination of the following catecholamine metabolites in plasma:
- Metanephrines
- Normetanephrine
[Probable pheochromocytoma if levels exceed three times normal; if metanephrines are borderline elevated, repeat test first; note possible interfering medications]
Alternative: determination of the catecholamines epinephrine and norepinephrine or the catecholamine metabolites metanephrines and normetanephrines in acidified 24 h urine.
If malignant (malignant) pheochromocytoma is suspected, dopamine and homovanillic acid should also be determined.
Clonidine suppression test
In case of clinical suspicion of a pheochromocytoma and only moderately elevated catecholamine metabolites, it is recommended to perform a confirmatory test: clonidine inhibition test (clonidine suppression test). For this, the systolic blood pressure value must be > 120 mmHg.
See Clonidine suppression test.Test result in the presence of pheochromocytoma:
- A decrease in plasma metanephrine by <40% of baseline is highly suggestive of pheochromocytoma with high sensitivity and specificity.
With basal levels usually markedly elevated (epinephrine > 85 ng/l, norepinephrine > 275 ng/l), no decrease in plasma norepinephrine/epinephrine levels is observed in pheochromocytoma.
If pheochromocytoma is detected, genetic workup is recommended in the following cases:
- Patient <20 years of age
- Bilateral pheochromocytoma
- Positive family history
- Paragangliomas
