Determination of reference intervals for plasma metanephrine and normetanephrine

Aim: The use of plasma metanephrine and normetanephrine for the investigation of phaeochromocytomas and paragangliomas (PPGLs) requires appropriate reference intervals.1 The current upper cut-offs at Monash Pathology were 500 pmol/L for metanephrine and 900 pmol/L for normetanephrine. Given the low prevalence of PPGLs, false-positive results (due to upper cut-offs set too low) are a problem. We attempted to determine the optimal upper cut-offs with improved specificity without compromising sensitivity.