Question: I have recently been tested for a pheochromocytoma. I am on Inderal for my high blood pressure and am also on two meds for depression and pain (amitryptiline and Cymbalta). Will the use of theses meds interfere with my test results? I have been told yes by my mother who of course has already been through three surgeries with my father and brother, but my family practitioner says no. Should I request a test retake without meds? – Shelley B., Massachusetts

Response: Shelley’s mother is correct and the family Doctor is not. Although, Inderal is not much of a problem, Cymbalta and Amitrytiline may result in significant interference to biochemical tests used to diagnose pheo. Both drugs are monoamine re-uptake blockers. Amitrytiline is a particularly well established problem (see figure 3 and table 2 of the attached PDF). It is a tricyclic antidepressant that blocks re-uptake of norepinephrine by sympathetic nerves, thereby increasing plasma and urinary levels of the transmitter, its O-methylated metabolite, normetanephrine, and also VMA. As a consequence patients taking this drug, or other tricyclics, have a high likelihood of false-positive elevations of plasma and urinary norepinephrine, normetanephrine and VMA.

Nevertheless, patients on these drugs can still have these tests carried out. If the tests come out negative (normal), then there is nothing to worry about. However, if they come out positive and especially in the grey area, then it is probable that the elevation is due to the tricyclic and not a pheo. Amitrytiline has a very long half life requiring up to a week or more for patients to be off the drug before testing. This can be problematic for those reliant on the medication. However, in many cases this is about the only way to exclude an effect of the drug and allow appropriate interpretation of test results.

Tricyclics and other monoamine uptake blockers can also interfere with MIBG imaging, preventing uptake of the agent into tumors, and thereby causing false-negative results.

If you are taking a tricyclic as an antidepressant or for some forms of chronic pain and insomnia, be sure to share this information with your doctor. – Graeme Eisenhofer, Ph.D., U.S. National Institutes of Health. See also Eisenhofer et al, Biochemical Diagnosis of Pheochromocytoma, Journal of Clinical Endocrinology and Metabolism, 2003, 88(6):2656-2666 and Goldstein, Eisenhofer, et al., Diagnosis and Localization of Pheochromocytoma, Hypertension, 2004 May;43(5):907-10. Epub 2004 Mar 15.

Testing Children for Pheo

Question: The preferred test for a pheo – it is more specific and more reliable than the 24-hour urine collection, and not much more money. I know that, but needles are worse than surgery for both of my kids. I always seek out the most experienced pediatric phlebotomist in the hospital. We have tried Emla cream to anesthetize the skin, without much success. It tends to make the veins constrict, which ends up hurting more. The freezing spray seems to work better, but there is still a problem with constriction. I wish there were something better. We count with our kids and that seems to distract them somewhat. I also have them drink a lot of water – it helps to be well hydrated. – Alison E., Texas

Response: We do have considerable data now to show that the Plasma Free Metanephrines test is indeed more reliable than urinary catecholamines (24-hour urine). The other problem is that a complete urinary collection can be difficult. We are still building tables of age-adjusted ranges for children with both of these tests.

As you mention the downside for plasma assays is that blood sampling can be stressful for some children, so yes anxiety can be a problem. For this reason the use of a rest period and an indwelling IV (rather than needle stick) is more important in children than in adults. – Graeme Eisenhofer, Ph.D., NIH. See also Eisenhofer et al, Biochemical Diagnosis of Pheochromocytoma, Journal of Clinical Endocrinology and Metabolism, 2003, 88(6):2656-2666

As printed in the VHL Family Forum 14:1, April/May 2006. Updated references August 2006. For permission to reprint, please contact VHL Family Alliance, editor@vhl.org. Further information is available from the VHL Family Alliance, info@vhl.org.