Endocrine Abstracts

Background

False positive results are common in the screening of pheochromocytoma. Even in high risk patients with disorders related to multiple endocrine neoplasia it’s crucial to exclude possible interferences with analytical methods.

Clinical case

A 69 year-old man was submitted to total thyroidectomy, due to a 11 mm hypoechogenic nodule suspicious of papillary carcinoma (FNA). Histology confirmed medullary carcinoma pT1b. The surgery department ordered the screening for primary hyperparathyroidism and pheochromocytoma and sent the case to Endocrinology. Initial 24 h urinary metanephrines (HPLC) were increased [861 μg/24 h (<302)], but urine was collected shortly after surgery. The patient didn’t have paroxistic symptoms and the abdominal CT showed normal adrenal glands. The tests were repeated one month later without known interferences (taking tamsulosin, atorvastatin, omeprazole and levothyroxine): metanephrines were normal in plasma and urine [plasmatic 38 pg/ml (<65), urinary 132 μg/24 h (<302)], but the urinary normetanephrines were elevated 4 fold [2005 μg/24 h (<527) while plasmatic remained normal [110 pg/ml (<196)]. RET gene study didn’t show mutations. Given the discrepancy of the results, the metanephrines and normetanephrines were repeated after tamsulosin withdrawal for 15 days, which resulted in normal plasmatic and urinary levels [24 h urinary metanephrines 158 μg/24 h (<302), normetanephrines 213 μg/24 h (<527); plasmatic metanephrines 45 pg/ml (<65), normetanephrines 35 pg/ml (<196)].

Discussion: There are many interferences with nor/metanephrine tests. Anesthetics and some analgesics are known interferences, but there is a comprehensive list of possible medications associated with false positive results. In this case, the first metanephrines were interpreted as interference caused by surgery and anesthetics given that metanephrine levels normalized later. After hospital discharge normetanephrines increased in spite of low risk of disease (RET gene negative for mutations, normal adrenal glands in abdominal CT). Tamsulosin is an alpha-adrenergic blocker with local prostatic action, unexpected to have significant changes in normetanephrines, but only after 15 days of drug discontinuation the results were normal.