Endocrine Abstracts

Background: Plasma normetanephrine levels are an annual screening tool for detecting paragangliomas in SDHB mutation carriers. Sensitivity is increased when patients are fasting and recumbent prior to phlebotomy, to allow use of age-adjusted reference ranges rather than the 1180 pmol/l upper limit for ambulatory patients of any age. We present our clinic’s results of samples taken after 30 minutes of recumbency to determine if applying age-adjusted ranges guides radiologists in identifying small paragangliomas.

Methods: Plasma normetadrenaline and reports of magnetic resonance with diffusion-weighted imaging from neck to pelvis were assessed for 170 adults with a pathogenic SDHB mutation. After excluding those without local plasma results and imaging in the past 3 years and those with known secretory paraganglioma, the results of 122 patients were separated into five age categories from the literature. Patients with levels above the age-related limit and below 1180 pmol/l were highlighted for radiology re-review.

Results: Ten individuals had levels above their respective age-adjusted thresholds: three patients, each over 70 years, had plasma normetadrenaline exceeding 1180 pmol/l without paraganglioma identified; seven patients had a level exceeding the upper limit of only the age-adjusted recumbent range which led to three radiological findings: two have <2cm phaeochromocytomas and one has a para-aortic cluster of cells with restricted diffusion suggestive of paraganglioma.

Conclusions: Utilising recumbent, age-adjusted reference ranges allows those patients with potential for a small secretory lesion to be highlighted to the reporting radiologist. Where recommended age brackets increment by decade until the age of 60, existing data does not provide a suitable range for those over 70 years. Given the low rate and small size of tumour detection in this cohort with "intermediate" normetadrenaline, the age-adjusted range is likely less useful for screening hypertensive patients without a familial syndrome so recumbency can be prioritised for those with a genetic predisposition.