If your doctor is suspicious of pheochromocytoma there are some standard tests that are initially performed. The 24 hour urine tests for catecholamines, metanephrines and VMA are fairly standard in the beginning stages of a diagnosis. These must be performed correctly: the urine specimen must be kept refrigerated during collection, and an acid preservative added to the collection bottle. In some cases, unless an individual has an episode during collection, the urine test could be negative, even with a pheochromocytoma present. There is a blood test available which tests Plasma Metanephrines and Catecholamines, which has been approved for diagnosis of pheochromocytoma. This test is available through the National Institutes of Health, and commercially through the Mayo Clinic. Some pheochromocytoma researchers believe that because of the high sensitivity of the plasma free metanephrines test and the low incidence of the tumor, that plasma free metanephrines should be carried out as the first test. If that is not available, then the next best test is urinary fractionated metanephrines - but not urinary TOTAL metanephrines. Both tests may be combined with measurements of plasma or urinary catecholamines.
How is Pheochromocytoma treated?
Once a diagnosis of pheochromocytoma has been established and the tumor located, surgical removal of the tumor is standard treatment if possible. This is not always as simple as it sounds. Some patients with pheochromocytoma find that it is difficult for the location of the tumor to be discovered. There are also cases of "quiet" pheochromocytomas which take longer to find and remove. For pheochromocytoma surgery, it is vital to ask your surgeon how many patients he or she has operated on specifically for this type of tumor. An experienced surgeon will do no less than 3 to 4 pheochromocytoma surgeries in a year.
What makes the plasma metanephrine test different?
First, the free metanephrines are produced continuously within pheochromocytoma tumor cells from catecholamines leaking from storage vesicles within the cell cytoplasm. Thus, these metabolites are produced independently of catecholamine released by tumors. This has advantages since catecholamine release can be episodic or relatively non-existent in some pheochromocytomas. Second, metanephrines commonly measured in urine are different metabolites. They are actually sulfate conjugated, require an additional metabolic step for synthesis and are consequently produced in different parts of the body than the free metanephrines. Third, the advantages of a plasma test over a urine test outweigh the disadvantages. Most urine tests have a lesser accuracy rate, whereas the plasma metanephrine test has a much higher accuracy rate.
What is the accuracy of the plasma free metanephrines test?
Testing results indicate a sensitivity of 99% compared to 63% for VMA and 83% to 85% for urinary or plasma catecholamines.
What substances interfere with the results of 24 hour urine tests?
Many drugs can potentially interfere with assays of catecholamines and any other substances, but this often depends on the method and laboratory. One facility can have machines and equipment that vary from that being used by another facility. Also, whether it is a problem or not depends on the level of expertise and competency of the operator running the assay. Caffeine, vanilla, vanilla extract, and bananas are known problems for urine testing. Listing these interferences is best left up to the individual laboratory responsible for the test.
What substances interfere with the plasma metanephrine test?
Specifically, caffeine is a problem both directly and indirectly. Acetaminophen or any drugs containing acetaminophen can be a problem. No other medicinal source of interference has been identified. Clonidine or its metabolites show up in the chromatograms but they aren't a problem. Again, listing these interferences is best left up to the individual laboratory responsible for the test being performed. If the patient is not given a list of known interferences, be sure to insist on having a copy.
What if the results are negative in the 24 hour catecholamine urine test?
It is still recommended that the plasma metanephrine test be performed to confirm or eliminate the diagnosis of pheochromocytoma, particularly if the symptoms are episodic. The 24 hour urine tests are not always successful at picking up intermittently secreting tumors.
List of symptoms of Pheochromocytoma
Symptoms vary greatly with each patient. Sterotyped textbook cases of Pheochromocytoma are rare. Symptoms can include:
Weight loss or gain
Angina Chest Pain
Clammy skin Cold skin
Feeling of impending doom
Paresthesia (tingling, prickling, numbness or burning sensations)
Lenders J.W.M., K. Pacak, M.M. Walther, W.M. Linehan, M. Mannelli, P. Friberg, H.R. Keiser, D.S. Goldstein and G. Eisenhofer. Biochemical diagnosis of pheochromocytoma: Which test is best? Journal of the American Medical Association 287: 1427-1434, 2002.
Eisenhofer, G.; Lenders, J.W.M.; Linehan, W.M.; Walther, M.M.; Goldstein, D.S.; Keiser, H.R. "Plasma normetanephrine and metanephrine for detecting pheochromocytoma in Von Hippel-Lindau disease and multiple endocrine neoplasia type 2." N.E.J.M. 340:24 (1999) 1872-1879.
Eisenhofer, G; Walther, W.M., et al, "Plasma Metanephrines: Novel and Cost Effective Test for Pheochromocytoma," Proceedings of the 1st International Meeting on Adrenal Diseases, Brazilian Journal of Medical and Biological Research, September 7, 1999.