title: Is supine rest necessary before blood sampling for plasma metanephrines?
abstract: BACKGROUND
  The impact of blood sampling in sitting vs supine positions on measurements of plasma metanephrines for diagnosis of pheochromocytoma is unknown.
  
  
  METHODS
  We compared plasma concentrations of free metanephrines in samples from patients with primary hypertension obtained after supine rest with those obtained in the sitting position without preceding rest. We also assessed the effects on diagnostic test performance retrospectively in patients with and without pheochromocytoma, and we calculated cost-effectiveness for pheochromocytoma testing.
  
  
  RESULTS
  Upper reference limits of plasma free metanephrines were higher in samples obtained from seated patients without preceding rest than from supine patients with preceding rest. Application of these higher upper reference limits to samples from supine patients with pheochromocytoma decreased the diagnostic sensitivity from 99% to 96%. In patients without pheochromocytoma, adjusting the plasma concentration for the effects of sitting while preserving the 99% sensitivity by use of the supine upper reference limits increased the number of false-positive test results from 9% to 25%.
  
  
  CONCLUSIONS
  To preserve high diagnostic sensitivity we recommend the use of upper reference limits determined from blood samples collected in the supine position. Under these conditions, negative test results for blood samples obtained with patients sitting are as effective for ruling out pheochromocytoma as negative results from samples obtained after supine rest. Repeat testing with samples obtained in the supine position offers a cost-effective approach for dealing with the increased numbers of false-positive results expected after initial sampling in the sitting position.
authors.affiliation: Department of Internal Medicine, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands. j.lenders@aig.umcn.nl
authors.forename: Jacques W M
authors.initials: JW
authors.lastname: Lenders
authors.forename: Jacques J
authors.initials: JJ
authors.lastname: Willemsen
authors.forename: Graeme
authors.initials: G
authors.lastname: Eisenhofer
authors.forename: H Alec
authors.initials: HA
authors.lastname: Ross
authors.forename: Karel
authors.initials: K
authors.lastname: Pacak
authors.forename: Henri J L M
authors.initials: HJ
authors.lastname: Timmers
authors.forename: C G J Fred
authors.initials: CG
authors.lastname: Sweep
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000175:diagnosis; D000328:Adult; D000368:Aged; D001800:Blood Specimen Collection / Q000191:economics; D003362:Cost-Benefit Analysis; D005260:Female; D006801:Humans; D008297:Male; D008676:Metanephrine / Q000097:blood*; D008875:Middle Aged; D010673:Pheochromocytoma / Q000175:diagnosis; D010949:Plasma; D012146:Rest; D012189:Retrospective Studies; D016683:Supine Position
chemical_list: D008676:Metanephrine