Evaluating the optimum rest period prior to blood collection for fractionated plasma free metanephrines analysis

• Published in: Practical laboratory medicine Vol. 5; pp. 39 - 46
• Main Authors: Griffin, T.P., Casey, R., Wall, D., Bell, M., O'Shea, P.M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.2016; Elsevier
• Subjects: Diagnostic sensitivity; Diagnostic specificity; Phaeochromocytoma; Plasma metanephrine; Plasma normetanephrine; Diagnostic sensitivity; Plasma normetanephrine; Plasma metanephrine; Diagnostic specificity; Phaeochromocytoma
• ISSN: 2352-5517; 2352-5517
• DOI: 10.1016/j.plabm.2016.05.001

The high diagnostic accuracy of plasma metanephrines (PMets) in the diagnosis of Phaeochromocytoma/Paraganglioma (PPGL) is well established. Considerable controversy exists regarding optimum sampling conditions for PMets. The use of reference intervals that do not compromise diagnostic sensitivity is recommended. However, the optimum rest period prior to sampling has yet to be clearly established. The aim of this study was to evaluate PMets concentrations in paired blood samples collected following 30 and 40min seated-rest prior to sampling, in patients in whom it was clinically reasonable to suspect that PPGL may be present. A retrospective cross-sectional study design was used. PMets results from paired blood samples collected after 30 and 40min seated-rest between January 2009 and June 2015 were recorded. Results were interpreted using reference intervals established in subjects seated and supine. A total of 410 patient results were eligible for analysis. There was no statistical difference between plasma normetanephrine (NMN) or metanephrine (MN) concentrations in samples collected following 30 and 40min seated-rest in subjects with PPGL (n=11), post-resection of PPGL (n=20) or in whom PPGL was excluded (n=379). Using reference intervals established in the seated position, diagnostic sensitivity was 100% at 30min and 90.9% at 40min. Diagnostic specificity was approximately 95% at both time points. When supine reference intervals were used, diagnostic sensitivity was 100% and diagnostic specificity was reduced by ≈22% at both time points. Based on these data, we recommend at most 30min continuous rest prior to sampling for PMets measurement.