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Rheumatoid factor and falsely elevated results in commercial immunoassays: data from an early arthritis cohort.

Authors
  • Gehin, Johanna E1, 2
  • Klaasen, Rolf A3
  • Norli, Ellen S4, 5
  • Warren, David J3
  • Syversen, Silje W4
  • Goll, Guro L4
  • Bjøro, Trine3, 6
  • Kvien, Tore K6, 4
  • Mjaavatten, Maria D4
  • Bolstad, Nils3
  • 1 Department of Medical Biochemistry, Oslo University Hospital-Radiumhospitalet, Box 4953 Nydalen, 0424, Oslo, Norway. [email protected] , (Norway)
  • 2 Faculty of Medicine, University of Oslo, Oslo, Norway. [email protected] , (Norway)
  • 3 Department of Medical Biochemistry, Oslo University Hospital-Radiumhospitalet, Box 4953 Nydalen, 0424, Oslo, Norway. , (Norway)
  • 4 Division of Rheumatology and Research, Diakonhjemmet Hospital, Oslo, Norway. , (Norway)
  • 5 Department of Rheumatology, Martina Hansens Hospital, Sandvika, Norway. , (Norway)
  • 6 Faculty of Medicine, University of Oslo, Oslo, Norway. , (Norway)
Type
Published Article
Journal
Rheumatology International
Publisher
Springer-Verlag
Publication Date
May 04, 2021
Identifiers
DOI: 10.1007/s00296-021-04865-9
PMID: 33944985
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

The aim of the study was to assess RF cross-reactivity to animal antibodies used in immunoassays, and to test if selected commercial immunoassays are vulnerable to interference from RF, causing false test results. Our study included samples from patients with RF-positive rheumatoid arthritis (RA) and controls (patients with RF-negative RA and psoriatic arthritis), included in an early arthritis-cohort. Reactivity to mouse IgG1, mouse IgG2a, rabbit IgG, bovine IgG, sheep/goat IgG and human IgG was analysed using in-house interference assays. RF-positive sera with strong reactivity to mouse IgG1 were analysed in three commercial immunoassays. To reveal interference, results before and after addition of blocking aggregated murine IgG1 were compared. Samples from 124 RF-positive RA patients and 66 controls were tested. We found considerably stronger reactivity toward animal antibodies, particularly mouse IgG1 (73% vs. 12%) and rabbit IgG (81% vs. 6%), in sera from RF-positive RA-patients compared to controls (p < 0.001). After selecting samples for testing in commercial assays, interference was revealed in 6/30 sera in the Architect β-hCG assay, 7/10 sera in the 27-plex cytokine assays, and in 2/33 samples in the Elecsys Soluble Transferrin Receptor assay. Our study revealed considerable RF reactivity to animal antibodies used in immunoassays and RF was associated with falsely elevated results in immunoassays used in clinical care and research. Clinicians, laboratorians, researchers and assay manufacturers must be alert to the risk of falsely elevated test results in RF-positive RA patients.

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