title: Limited value of testing for intrinsic factor antibodies with negative gastric parietal cell antibodies in pernicious anaemia.
abstract: BACKGROUND
  The appropriate testing strategy for diagnosing pernicious anaemia using gastric parietal cell (GPC) and/or intrinsic factor antibodies (IFA) is controversial. Intrinsic factor antibodies are found in only about 70% of cases. Indirect immunofluorescence screening for gastric parietal cell antibodies is more sensitive, labour intensive, and less specific.
  
  
  METHODS
  The frequency of antibody positivity (IFA and/or GPC) was retrospectively examined in patients tested for both autoantibodies over a three-year period. It was investigated whether B12 levels were related to antibody status. These findings were validated in a prospective study of IFA in 91 GPC negative patients with low B12 levels.
  
  
  RESULTS
  Of 847 samples identified in the retrospective study, 4 (0.47%) were positive for only intrinsic factor antibodies, 731 (86.3%) positive for GPC alone, and 112 (13.2%) for both. Student t test on log-transformed data showed B12 levels had no bearing on autoantibody status. 91 consecutive patients with low B12 levels were tested for both autoantibodies; all were negative for gastric parietal cell antibodies. Only one sample was positive for intrinsic factor antibody using the porcine intrinsic factor assay, but was negative by a human recombinant intrinsic factor-based ELISA.
  
  
  CONCLUSIONS
  This study provides evidence that testing for gastric parietal cell antibodies is an appropriate screening test for pernicious anaemia, with intrinsic factor antibodies reserved for confirmatory testing or in patients with other autoantibodies that mask the GPC pattern; B12 levels are not related to autoantibody status.
authors.affiliation: Path Links Immunology, Scunthorpe General Hospital, Scunthorpe, UK. sujoykhan@gmail.com
authors.forename: S
authors.initials: S
authors.lastname: Khan
authors.forename: C
authors.initials: C
authors.lastname: Del-Duca
authors.forename: E
authors.initials: E
authors.lastname: Fenton
authors.forename: S
authors.initials: S
authors.lastname: Holding
authors.forename: J
authors.initials: J
authors.lastname: Hirst
authors.forename: P C
authors.initials: PC
authors.lastname: Doré
authors.forename: W A C
authors.initials: WA
authors.lastname: Sewell
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000752:Anemia, Pernicious / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods; D006801:Humans; D007437:Intrinsic Factor / Q000276:immunology*; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D010295:Parietal Cells, Gastric / Q000276:immunology*; D011446:Prospective Studies; D012189:Retrospective Studies; D014805:Vitamin B 12 / Q000097:blood
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D007437:Intrinsic Factor; D014805:Vitamin B 12