From the Guidelines
Pheochromocytoma testing should begin with biochemical confirmation through measurement of plasma free metanephrines or 24-hour urinary fractionated metanephrines and catecholamines, as recommended by the most recent guidelines 1. The diagnosis of pheochromocytoma is crucial due to its potential to cause life-threatening hypertensive crises if not identified before procedures or surgery. The following laboratory tests and diagnostic evaluations are used:
- Biochemical confirmation through measurement of plasma free metanephrines or 24-hour urinary fractionated metanephrines and catecholamines, with plasma free metanephrines being the preferred screening test due to its high sensitivity and specificity 2, 1.
- Imaging studies, typically starting with CT or MRI of the abdomen and pelvis with contrast to locate the tumor, if biochemical tests are positive.
- Functional imaging such as 123I-MIBG scintigraphy, 18F-FDG PET/CT, or 68Ga-DOTATATE PET/CT may be necessary for cases requiring additional localization.
- Genetic testing is also recommended for all patients with pheochromocytoma, as approximately 40% have germline mutations in susceptibility genes like RET, VHL, NF1, SDHA, SDHB, SDHC, SDHD, and TMEM127 3, 2. Before testing, patients should avoid medications that can interfere with results, including tricyclic antidepressants, acetaminophen, phenoxybenzamine, and levodopa 3, 2. It is essential to note that the diagnosis of pheochromocytoma should be entertained in a hypertensive patient with a combination of headaches, palpitations, and sweating, typically occurring in an episodic fashion, with a diagnostic specificity of 90% 2. The best approach is to follow the most recent guidelines, which recommend screening for pheochromocytoma with plasma or 24-hour urinary metanephrines in patients with adrenal incidentalomas that display ≥ 10 HU on non-contrast CT or who have signs/symptoms of catecholamine excess 4.
From the Research
Laboratory Tests for Pheochromocytoma
- Biochemical tests are used to diagnose pheochromocytoma, including: + Plasma free metanephrines 5, 6, 7, 8, 9 + Urinary fractionated metanephrines 5, 6, 7, 8 + Urinary catecholamines 6, 9 + Urinary vanillylmandelic acid 6
- These tests measure the levels of catecholamines and their metabolites in the blood and urine.
Diagnostic Evaluations
- Radiological imaging tests are used to localize the tumor, including: + Computed tomography (CT) 5, 7 + Magnetic resonance imaging (MRI) 5, 7
- Functional imaging tests are used to assess the tumor's functionality, including: + Scintigraphy with (123)I-metaiodobenzylguanidine (MIBG) 5 + Scintigraphy with (131)I-MIBG 5 + Positron emission tomography (PET) with (18)F-F-fluorodopamine (F-DA) 5 + Single photon emission computed tomography 7
Test Sensitivity and Specificity
- Plasma free metanephrines have high sensitivity (99%) and specificity (89%) for diagnosing pheochromocytoma 6
- Urinary fractionated metanephrines have high sensitivity (97%) and specificity (69%) for diagnosing pheochromocytoma 6
- Urinary catecholamines have high sensitivity (100%) and specificity (94%) for diagnosing pheochromocytoma 9
Preanalytical Factors
- Preanalytical factors, such as drug interference, can affect the accuracy of biochemical tests for pheochromocytoma 8
- It is essential to consider these factors when interpreting test results and to use methods that minimize interference, such as liquid chromatography tandem mass spectrometry (LC-MS/MS) 8