MON-220 Real World Performance of Urinary and Plasma Metanephrine Assays in Diagnosing Phaeochromocytoma/Paraganglioma

Introduction: Diagnosis of pheochromocytoma/paraganglioma (PPGL) can be challenging. Plasma metanephrines have highest sensitivity (96-99%) yet lowest specificity (85%)(1) whereas 24-hour urinary metanephrines have 87.5% sensitivity and 99.7% specificity. Diagnostic accuracy depends on factors such as patient positioning and medications, questioning its potential value in a hospital setting. Methods: The audit was performed in a hospital which caters to a population of 400,000. Data was collected retrospectively on patients who had a request for plasma or urine metanephrines from March 2018 – September 2018. Results: A total of 85 patient order requests (58% male, 42% female) were reviewed; only 2 patients were ultimately diagnosed with a pheochromocytoma. The mean age of patients was 48 years. The most common indication for requests was hypertension (64 patients). Locations of order requests included 42% from outpatient clinics, 32% inpatient requests, 18% from Ambulatory Care, 6% by A&E and 2% by GP. Of the 27 (32%) inpatient requests, 10 had positive results: 1 diagnosed with primary aldosteronism, 1 with hypercortisolism and the others had no definite diagnosis. 8/10 patients with positive results did not have a repeat test. Focusing on plasma metanephrines, 52% plasma metanephrines samples were negative, 22% were positive and 26% were not processed due to laboratory error. From the 19 positive plasma metanephrines, adrenal adenoma was present in 7 patients (from this group, 1 was referred for surgery with confirmed diagnosis of pheochromocytoma), 1 patient’s MIBG scan was negative and 1 diagnosis of stress-related raised metanephrines was made. The remaining 10 patients did not undergo an adrenal scan. 9 out of 18 cases with positive urine metanephrines had an adrenal adenoma. In 7/9, plasma metanephrines were positive, the remaining 2 had negative plasma metanephrines. 34 cases with initial negative test still had another urine/plasma metanephrines performed with similar negative result. Furthermore <50% of the positive urine or plasma metanephrines were referred to and reviewed by the Endocrine team. Discussion: This audit highlights the potential pitfalls of investigating PPGL with plasma and urinary metanephrines, and in fact raises the question of its accuracy as an inpatient diagnostic tool as none of the positive inpatient tests resulted in a diagnosis of PPGL. Inappropriate urine and plasma metanephrines requests cause financial burden and patient anxiety. Even with outpatient requests, few positive results led to a PPGL diagnosis. Patient selection and conditions of testing must be more rigorously scrutinised and threshold for positive result must be raised for specificity of the test to be improved in ‘real world’ conditions. References: 1. Lenders JW al. Biochemical diagnosis of pheochromocytoma: which test is best? JAMA. 2002.