Background: The screening investigation of choice for phaeochromocytomas (PHAEO) and paragangliomas (PGL) in the UK is usually a 24 h urine collection for fractionated metadrenalines +/− free catecholamines. These assays have high diagnostic sensitivity (approaching 98%) but lower specificity.
Aim: To review causes of false positive (FP) catecholamine and metabolite results in our centre over a 12-year period.
Methods: Data were collected on all patients who presented to our endocrine department with a histologically confirmed diagnosis of PHAEO or PGL between 1997 and 2009. This was compared with a biochemistry database capturing all patients with raised urinary catecholamines and/or metadrenalines. A test was deemed to be FP when repeat biochemistry and/or radiology (CT/MRI/MIBG) was consistently negative. Clonidine-suppression tests were not performed.
Results: Fifty-nine patients with PHAEO or PGL were identified and compared with 57 FP results in 47 patients (elevated metadrenaline n=11, normetadrenaline n=11, adrenaline n=7, noradrenaline n=17, dopamine n=11). Compared with PHAEO/PGL, FP typically showed only moderately elevated catecholamines/metadrenalines: results were no higher than 1.75 (adrenaline), 1.8 (noradrenaline), 1.8 (dopamine), 2.9 (metadrenaline) or 3.1 (normetadrenaline)×upper limit of normal (ULN) (100% specificity). Potential drugs causing FP results included methyldopa (n=4), amitryptiline (n=2), beta blockers (n=5), calcium channel blockers (n=5) and alpha blockers (n=3). Three patients with FP results were pregnant, a further 5 had high urinary volumes, 2 had evidence of adrenal infarction (repeat scans normal) and one patient was noted to have obstructive sleep apnoea (OSA).
Conclusions: False positive urinary catecholamines and metadrenalines tend to cluster around the ULN. Factors such as medications, pregnancy, urine volume, adrenal infarction and OSA should be considered as causes of FP findings where biochemical results are only modestly elevated.