title: Diagnostic value of glucose-6-phosphate isomerase in rheumatoid arthritis.
abstract: BACKGROUND
  Although glucose-6-phosphate isomerase (G6PI), anti-G6PI antibodies and G6PI-containing immune complexes (G6PI-CIC) have proved high expression in patients with rheumatoid arthritis (RA), comprehensive evaluation of the G6PI-derived markers, G6PI antigen, anti-G6PI Abs, G6PI-CIC and G6PI mRNA, in the diagnosis of RA remains necessary.
  
  
  METHODS
  We measured G6PI antigen, anti-G6PI Abs, C1q/G6PI-CIC as well as anti-cyclic citrullinated peptide antibodies (anti-CCP Abs) in serum and concomitantly synovial fluid (SF) by ELISA in RA, other rheumatic diseases and healthy controls. The G6PI mRNA expression in peripheral blood mononuclear cells (PBMCs) was assessed with real-time PCR.
  
  
  RESULTS
  As compared with non-RA patients, RA patients had increased levels of G6PI antigen, anti-G6PI Abs, C1q/G6PI-CIC and G6PI mRNA expression in sera or PBMCs, and increased levels of G6PI and C1q/G6PI-CIC in SF. The serum G6PI levels in RA patients positively correlated with anti-G6PI Abs, C1q/G6PI-CIC, G6PI mRNA, anti-CCP Abs, RF, CRP and ESR, respectively. The area under curve analyses demonstrated that serum G6PI had the best discriminating power for RA and active RA followed by C1q/G6PI-CIC, anti-G6PI Abs and G6PI mRNA. The simultaneous use of serum G6PI and anti-CCP Abs assays in the form of either of them tested positive gave improved sensitivities of 88.1% for RA and 95.8% for active RA.
  
  
  CONCLUSIONS
  Despite the elevated expression of all G6PI-derived markers in RA, the serum G6PI has the best discriminating power among the four G6PI-derived markers. The serum G6PI determination either alone or in combination with anti-CCP Abs improves the diagnosis of RA.
authors.affiliation: Department of Clinical Laboratory, Shanghai East Hospital, Tongji University School of Medicine, 150 Ji Mo Road, Shanghai, 200120, China. flieying@hotmail.com
authors.forename: Lie Ying
authors.initials: LY
authors.lastname: Fan
authors.forename: Ming
authors.initials: M
authors.lastname: Zong
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
authors.forename: Li Shan
authors.initials: LS
authors.lastname: Sun
authors.forename: Qin
authors.initials: Q
authors.lastname: Ye
authors.forename: Yuan Yuan
authors.initials: YY
authors.lastname: Ding
authors.forename: Jian Wei
authors.initials: JW
authors.lastname: Ma
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000941:Antigens / Q000097:blood / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000175:diagnosis* / Q000378:metabolism* / Q000473:pathology; D001323:Autoantibodies / Q000097:blood / Q000276:immunology / Q000378:metabolism; D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D015922:Complement C1q / Q000378:metabolism; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D005956:Glucose-6-Phosphate Isomerase / Q000097:blood / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013582:Synovial Fluid / Q000378:metabolism; D055815:Young Adult
chemical_list: D000941:Antigens; D001323:Autoantibodies; D015415:Biomarkers; D012333:RNA, Messenger; D015922:Complement C1q; D005956:Glucose-6-Phosphate Isomerase