title: Automated chemiluminescence-immunoassay for aldosterone during dynamic testing: comparison to radioimmunoassays with and without extraction steps.
abstract: BACKGROUND
  Measurements of aldosterone have become more common since the recognition that primary aldosteronism is a more frequent cause of hypertension than previously believed. Our aim was to compare concentrations reported by 4 assays for samples obtained after saline infusion during dynamic testing.
  
  
  METHODS
  We tested 104 participants (27 with primary aldosteronism, 30 with essential hypertension, and 47 healthy controls) with the intravenous saline infusion test (2.0 L isotonic saline over 4 h), with repetitive sampling. In all blood samples, aldosterone concentration was measured by an in-house RIA after extraction and chromatography, by 2 commercially available RIAs without extraction (Aldosterone Maia, Adaltis; Active Aldosterone, Diagnostics Systems Laboratories) and by an automated CLIA (Advantage, Nichols Institute Diagnostics).
  
  
  RESULTS
  Correlation coefficients for results of pairs of assays ranged from 0.74 to 0.98. Agreement between commercial assays and in-house RIA was best at the low to intermediate concentrations after saline infusion. Mean (SD) Adaltis and DSL RIA results were 2- to 3-times higher [healthy participants: 78 (25) ng/L and 56 (18) ng/L, respectively] than those obtained by Nichols CLIA [17 (8) ng/L] and in-house RIA [23 (18) ng/L]. Aldosterone concentrations measured by the Nichols CLIA were below the limit of detection (limit of the blank) in 27 of 47 healthy participants.
  
  
  CONCLUSIONS
  Aldosterone concentrations reported by the Adaltis and DSL nonextraction RIAs were consistently higher than those produced by the Nichols CLIA and the in-house RIA. The convenient Nichols CLIA showed better agreement with the in-house RIA, but the concentrations in healthy participants were frequently undetectable by this method. Uncritical application of cutoff values from the literature must be avoided.
authors.affiliation: Ludwig-Maximilians-University, Medizinische Klinik Innenstadt, Munich, Germany.
authors.forename: Caroline
authors.initials: C
authors.lastname: Schirpenbach
authors.forename: Lysann
authors.initials: L
authors.lastname: Seiler
authors.forename: Christiane
authors.initials: C
authors.lastname: Maser-Gluth
authors.forename: Felix
authors.initials: F
authors.lastname: Beuschlein
authors.forename: Martin
authors.initials: M
authors.lastname: Reincke
authors.forename: Martin
authors.initials: M
authors.lastname: Bidlingmaier
mesh_terms: D000328:Adult; D000450:Aldosterone / Q000097:blood*; D001322:Autoanalysis; D005260:Female; D006801:Humans; D006929:Hyperaldosteronism / Q000175:diagnosis*; D007118:Immunoassay; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D011863:Radioimmunoassay / Q000379:methods; D012016:Reference Values
chemical_list: D000450:Aldosterone