title: Norethisterone interference in testosterone assays.
abstract: BACKGROUND
  This article describes three patients in whom measured serum testosterone concentrations were found to be artifactually high due to interference from norethisterone medication. This interference was investigated further by distributing samples containing norethisterone through an external quality assessment scheme.
  
  
  METHODS
  Serum samples containing different concentrations of norethisterone were distributed to participants in the UK external quality assessment scheme (UK NEQAS) for female testosterone in order to assess the degree of interference from norethisterone in different commercially available immunoassay and liquid chromatography-tandem mass spectrometry methods for measurement of testosterone.
  
  
  RESULTS
  The results have shown that apparent serum testosterone concentrations in excess of 5 nmol/L may be obtained using the Roche E170 Modular immunoassay method for samples collected from patients taking norethisterone medication and this interference can be reproduced by adding norethisterone to serum samples.
  
  
  CONCLUSIONS
  Although the biggest interference is seen with the Roche system, there is a small effect in the Siemens ADVIA Centaur assay and some of the other immunoassays may also be affected to a much lesser extent. Norethisterone does not interfere in testosterone measurements obtained by liquid chromatography-tandem mass spectrometry.
authors.affiliation: Department of Clinical Biochemistry, Derriford Hospital, Plymouth UK.
authors.forename: Jinny
authors.initials: J
authors.lastname: Jeffery
authors.forename: Finlay
authors.initials: F
authors.lastname: MacKenzie
authors.forename: Geoff
authors.initials: G
authors.lastname: Beckett
authors.forename: Les
authors.initials: L
authors.lastname: Perry
authors.forename: Ruth
authors.initials: R
authors.lastname: Ayling
mesh_terms: D000293:Adolescent; D016477:Artifacts; D001774:Blood Chemical Analysis / Q000379:methods*; D003280:Contraceptives, Oral, Synthetic / Q000494:pharmacology*; D005260:Female; D006801:Humans; D009640:Norethindrone / Q000494:pharmacology*; D013739:Testosterone / Q000097:blood*
chemical_list: D003280:Contraceptives, Oral, Synthetic; D013739:Testosterone; D009640:Norethindrone
keywords: Steroid hormones; analytes; assay interference; testosterone