title: Plasma metanephrines in renal failure.
abstract: BACKGROUND
  Diagnosis of pheochromocytoma in renal failure poses a diagnostic dilemma due to lack of reliability of conventional urinary measurements of catecholamine excess. Measurements of the plasma metanephrines, normetanephrine and metanephrine (the O-methylated metabolites of norepinephrine and epinephrine), provide an alternative diagnostic test. The metanephrines may be measured as free metabolites or after a deconjugation step where measurements reflect mainly sulfate-conjugated metabolites. The influence of renal insufficiency states on these various measurements is unclear.
  
  
  METHODS
  Plasma free and deconjugated metanephrines and catecholamines in 17 patients on dialysis with end-stage renal disease and 19 patients with renal insufficiency (creatinine clearance, 5-78 mL/min) were compared with levels in 89 hypertensives, 68 healthy normotensives, and 51 patients with von Hippel-Lindau syndrome.
  
  
  RESULTS
  Patients with renal failure had up to two-fold higher plasma concentrations of catecholamines and free metanephrines, and more than 12-fold higher plasma concentrations of deconjugated metanephrines than comparison groups. Plasma free metanephrines and catecholamines were, respectively, within the 95% confidence intervals of reference groups in 75% and 42% of the dialysis patients, and in 74% and 68% of patients with renal insufficiency. In contrast, no dialysis patient and only half the renal insufficiency patients had plasma levels of deconjugated metanephrines within the reference intervals. Plasma levels of deconjugated metanephrines, but not free metanephrines, showed strong inverse relationships with creatinine clearance.
  
  
  CONCLUSIONS
  Plasma concentrations of free metanephrines are relatively independent of renal function and are, therefore, more suitable for diagnosis of pheochromocytoma among patients with renal failure than measurements of deconjugated metanephrines.
authors.affiliation: Clinical Neurocardiology Section, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20892-1620, USA. ge@box-g.nih.gov
authors.forename: Graeme
authors.initials: G
authors.lastname: Eisenhofer
authors.forename: Frans
authors.initials: F
authors.lastname: Huysmans
authors.forename: Karel
authors.initials: K
authors.lastname: Pacak
authors.forename: MacClellan M
authors.initials: MM
authors.lastname: Walther
authors.forename: Fred C G J
authors.initials: FC
authors.lastname: Sweep
authors.forename: Jacques W M
authors.initials: JW
authors.lastname: Lenders
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000175:diagnosis; D000328:Adult; D000368:Aged; D004837:Epinephrine / Q000097:blood; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood; D008297:Male; D008676:Metanephrine / Q000097:blood*; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D010673:Pheochromocytoma / Q000175:diagnosis; D051437:Renal Insufficiency / Q000097:blood*
chemical_list: D008676:Metanephrine; D009638:Norepinephrine; D004837:Epinephrine