Screening for pheochromocytoma: pitfalls and safety nets

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 37-82-Pheochromocytoma & Paraganglioma
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-54
Aoife Garrahy*1, Ruth Casey2, Marcia Bell1 and Paula O Shea3
1Galway University Hospital, Galway, Ireland, 2Cork Univ Hospital, Cork, Ireland, 3Galway University Hospital, Galway
Screening for pheochromocytoma: pitfalls and safety nets.

Garrahy A 1, Casey R 1, Bell M 1, O’ Shea P 2

1.            Dept of Endocrinology, Galway University Hospital, Galway, Ireland.

2.            Dept of Clinical Biochemistry, Galway University Hospital, Galway, Ireland.

Pheochromocytomas are rare neuroendocrine tumours. In this institution, 24hr urinary testing for total fractionated catecholamines and metanephrines is the standard approach for diagnosis. In cases where test results are equivocal (elevated but less than twice the respective upper reference limit), we repeat test for free fractionated metanephrines in plasma because of the superior specificity of this test. The aim of this study was to audit the biochemical screening strategy for pheochromocytoma and to review the follow-up of those patients with positive results.

The biochemistry database was interrogated to extract all records of biochemical screening for pheochromocytoma from January 2004 to June 2012. During that period, 2749 biochemical screens were performed, of which 110 (4%) were positive, mean age 52 years (SD 16), male 57.3%. Chart review found that 18 of 110 patients had confirmed pheochromocytoma on histology. In the remaining 92 patients, repeat screening was carried out in 47 (51%), with urinary screening performed in 35 (38%) and plasma screening in 1. All 45 patients (49%) in whom a repeat screen was not performed were subsequently scheduled for repeat biochemical screening using plasma free metanephrines. To date, appointments have been given to 14, 5 did not attend, 8 had normal plasma metanephrines and one had raised plasma metanephrines.

False positive results are often due to concomitant medication use. In our cohort, 50 patients (45.5%) were on interfering medications at time of testing. Commonly implicated drugs were beta blockers (10.9%), alpha blockers (6.4%), calcium channel blockers (5.5%), SSRIs (2.7%) and amytriptyline (2.7%). Of note, 9% of patients were on more than one interfering medication on initial testing.

The potential fatal consequences of a missed diagnosis justify the need for the high level of reliability of a positive test result. These findings suggest that appropriate follow-up of borderline elevated test results should first include repeat testing, preferably for free plasma metanephrine measurement.

Nothing to Disclose: AG, RC, MB, PO

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