Endocrine Abstracts

The recently published Endocrine Society Clinical Practice guideline on phaeochomocytoma and paraganglioma (PPGL) recommends measuring plasma metanephrines (PMets) with patients in the supine position after an overnight fast and using appropriately defined reference intervals.¹ Studies have shown higher diagnostic sensitivities using the latter pretesting criteria.² However, this testing protocol is resource intensive and arguably impractical in routine clinical practice. In our institution blood samples for PMets are collected with patients non-fasting and seated using reference intervals established accordingly. The aim of the present study was to assess the effects on diagnostic test performance retrospectively in patients who underwent PMets screening in our institution between 2009 and 2014 using reference intervals derived in subjects fasting and supine. A total of 150 patients were included in this study. There were 79 males (53%) and 71 females (47%). The mean age was 54.3 years (S.D. 6 years). A total of 45 (30%) patients would have had a positive test result based on the supine reference interval being applied vs a total of 8 (5.3%) patients who screened positive using the decision thresholds derived in seated subjects. There were 6 (4%) patients with histologically confirmed PPGL in this cohort and no case would have been missed using the non-fasting and seated reference intervals for PMets. The most common alternative diagnosis for the 39 patients who screened positive for PMets using the new supine reference interval but who did not have a diagnosis of PPGL was essential hypertension (n=19, 48.7%). This study demonstrates that the existing, more pragmatic pretesting protocol for PMets collection resulted in no false-negative biochemical screening for PMets over a 5-year period and that application of a supine reference interval would have resulted in 39 false-positive results in this same time period.

References: 1. J Clin Endocrinol Metab 2014 99 (6) 1915–1942.

2. Clin Endocrinol (Oxf) 2014 80 (4) 478–486.