ECE2013 Poster Presentations Endocrine tumours and neoplasia (66 abstracts)
Biochemical diagnosis of pheochromocytoma using plasma free normetanephrine, metanephrine and methoxytyramine: importance of supine sampling under fasting conditions
Roland Därr 1 , Mirko Peitzsch 1 , Christina Pamporaki 1 , Aleksander Prejbisz 2 , Martin Fassnacht 3, , Felix Beuschlein 4 , Hartmut Neumann 5 , Andrzej Januszewicz 2 , Jacques Lenders 6, & Graeme Eisenhofer 1
1University Hospital Dresden, Dresden, Germany; 2Institute of Cardiology, Warsaw, Poland; 3University Hospital Würzburg, Würzburg, Germany; 4Medical Clinic Innenstadt, LMU, Munich, Germany; 5University of Freiburg, Freiberg, Germany; 6Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.
Objective: To document influences of sampling of blood under supine fasting versus seated non-fasting conditions on diagnosis of pheochromocytoma using plasma concentrations of normetanephrine, metanephrine and methoxytyramine (P-NMN/MN/MTY).
Design and methods: P-NMN/MN/MTY were measured by liquid chromatography with tandem mass spectrometry in 695 patients at five centers, two of which complied with requirements for supine sampling after an overnight fast and three of which did not. Pheochromocytomas were found in 109 patients (60 non-compliant, 49 compliant) and not in 586 patients (144 non-compliant, 442 compliant).
Results: P-NMN/MN/MTY in patients with pheochromocytoma did not differ under compliant and non-compliant conditions. However, sampling under non-compliant compared to compliant conditions resulted in 50 and 40% higher (P<0.001) median plasma concentrations of NMN (84 vs 56 pg/ml) and MTY (17.3 vs 12.4 pg/ml) in patients without tumors. Upper cutoffs were also substantially higher under non-compliant compared to compliant conditions for both NMN (241 vs 144 pg/ml) and MTY (62 vs 33 pg/ml). Differences for MN were minimal. Use of upper-cut-offs calculated for non-compliant compared to compliant conditions resulted in substantially decreased diagnostic sensitivity (88.1 vs 98.2%). Use of upper-cut-offs calculated for compliant conditions was associated with a diagnostic specificity of only 78.5% for sampling under non-compliant conditions compared to 94.8% with compliant conditions.
Conclusions: High diagnostic sensitivity of P-NMN/MN/MTY for detection of PPGLs can only be guaranteed using upper-cut-offs of reference intervals appropriately calculated under supine fasting conditions. With appropriately estimated upper-cut-offs, sampling under seated non-fasting conditions can lead to a fivefold increase in false-positive results necessitating repeat sampling under supine fasting conditions.
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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