title: Comparisons of immunoassay and mass spectrometry measurements of serum estradiol levels and their influence on clinical association studies in men.
abstract: BACKGROUND
  Immunoassay-based techniques, routinely used to measure serum estradiol (E2), are known to have reduced specificity, especially at lower concentrations, when compared with the gold standard technique of mass spectrometry (MS). Different measurement techniques may be responsible for the conflicting results of associations between serum E2 and clinical phenotypes in men.
  
  
  OBJECTIVE
  Our objective was to compare immunoassay and MS measurements of E2 levels in men and evaluate associations with clinical phenotypes.
  
  
  METHODS
  Middle-aged and older male subjects participating in the population-based Osteoporotic Fractures in Men (MrOS) Sweden study (n = 2599), MrOS US (n = 688), and the European Male Aging Study (n = 2908) were included.
  
  
  METHODS
  Immunoassay and MS measurements of serum E2 were compared and related to bone mineral density (BMD; measured by dual energy x-ray absorptiometry) and ankle-brachial index.
  
  
  RESULTS
  Within each cohort, serum E2 levels obtained by immunoassay and MS correlated moderately (Spearman rank correlation coefficient rS 0.53-0.76). Serum C-reactive protein (CRP) levels associated significantly (albeit to a low extent, rS = 0.29) with immunoassay E2 but not with MS E2 levels. Similar associations of immunoassay E2 and MS E2 were seen with lumbar spine and total hip BMD, independent of serum CRP. However, immunoassay E2, but not MS E2, associated inversely with ankle-brachial index, and this correlation was lost after adjustment for CRP.
  
  
  CONCLUSIONS
  Our findings suggest interference in the immunoassay E2 analyses, possibly by CRP or a CRP-associated factor. Although associations with BMD remain unaffected, this might imply for a reevaluation of previous association studies between immunoassay E2 levels and inflammation-related outcomes.
authors: Centre for Bone and Arthritis Research, Sahlgrenska Academy, University of Gothenburg, Vita Stråket 11, SE-413 45 Gothenburg, Sweden. claes.ohlsson@medic.gu.se
authors: Claes
authors: C
authors: Ohlsson
authors: Maria E
authors: ME
authors: Nilsson
authors: Asa
authors: A
authors: Tivesten
authors: Henrik
authors: H
authors: Ryberg
authors: Dan
authors: D
authors: Mellström
authors: Magnus K
authors: MK
authors: Karlsson
authors: Östen
authors: Ö
authors: Ljunggren
authors: Fernand
authors: F
authors: Labrie
authors: Eric S
authors: ES
authors: Orwoll
authors: David M
authors: DM
authors: Lee
authors: Stephen R
authors: SR
authors: Pye
authors: Terence W
authors: TW
authors: O'Neill
authors: Joseph D
authors: JD
authors: Finn
authors: Judith E
authors: JE
authors: Adams
authors: Kate A
authors: KA
authors: Ward
authors: Steven
authors: S
authors: Boonen
authors: Gyorgy
authors: G
authors: Bartfai
authors: Felipe F
authors: FF
authors: Casanueva
authors: Gianni
authors: G
authors: Forti
authors: Aleksander
authors: A
authors: Giwercman
authors: Thang S
authors: TS
authors: Han
authors: Ilpo T
authors: IT
authors: Huhtaniemi
authors: Krzysztof
authors: K
authors: Kula
authors: Michael E J
authors: ME
authors: Lean
authors: Neil
authors: N
authors: Pendleton
authors: Margus
authors: M
authors: Punab
authors: Dirk
authors: D
authors: Vanderschueren
authors: Frederick C W
authors: FC
authors: Wu
authors: Liesbeth
authors: L
authors: Vandenput
mesh_terms: D000368:Aged; D015519:Bone Density; D002097:C-Reactive Protein / Q000032:analysis; D004958:Estradiol / Q000097:blood*; D006801:Humans; D007118:Immunoassay; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged
chemical_list: D004958:Estradiol; D002097:C-Reactive Protein
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