PS-C22-5: PLASMA METANEPHRINES PROVIDE GREATER SPECIFICITY THAN URINARY METANEPHRINES IN PATIENTS WITH OBSTRUCTIVE SLEEP APNEA: A PROSPECTIVE TRIAL

Abstract

Introduction: Pheochromocytoma and paraganglioma (PPGL), and obstructive sleep apnea (OSA) are important secondary causes of hypertension. Both plasma and urinary metanephrines have high diagnostic sensitivity and specificity for diagnosis of PPGL. Patients with OSA have increased nocturnal catecholamine release, which can lead to increased metanephrines production over 24 hours. We hypothesized that morning plasma metanephrines have a higher diagnostic accuracy than 24-hour urinary metanephrines in patients with OSA. Methods: We recruited patients undergoing polysomnography for suspected OSA. Plasma and 24-hour urinary metanephrines were measured. Patients with elevated metanephrines had repeated measurements of metanephrines, imaging and follow-up, to diagnose, or exclude, PPGL. Results: Seventy-six patients completed polysomnography and biochemical testing, of which 68 had OSA. One patient had a PPGL, while PPGL was excluded in the remaining patients. At baseline, OSA patients were more likely to have falsely-elevated urinary (17 of 67, 25.4%), than falsely-elevated plasma metanephrines (2 of 67, 2.9%) (P < 0.01). Seven patients had normal metanephrines on repeat testing. Nine patients with persistently elevated metanephrines underwent abdominal imaging: six patients had no PPGL, one had lipid-rich adrenal adenomas, one had indeterminate adrenal adenoma, and one had bladder tumor. This final patient with biopsy-proven bladder PPGL had marginally-elevated urinary metanephrines, but false-negative plasma metanephrines, due to the small tumor size. Falsely-elevated urine metanephrines were more common in patients with severe OSA (13 of 3, 38.2%), compared to moderate OSA (1 of 13, 7.7%) and mild OSA (3 of 20, 15%), P < 0.01. Falsely-elevated plasma and urine metanephrines were all due to elevation of normetanephrine, while metanephrine was normal in all patients. Declines in metanephrines were observed only in patients with OSA treated with continuous positive pressure ventilation, while those untreated had no improvements. Conclusion: In patients with OSA, metanephrines measured in plasma provide better specificity than those measured in urine for the diagnosis of PPGL. However, one patient with a small PPGL was missed by plasma metanephrines.