title: Antinuclear antibody prevalence in a general pediatric cohort from Mexico City: discordance between immunofluorescence and multiplex assays.
abstract: OBJECTIVE
  To characterize antinuclear antibody (ANA) prevalence according to distinct assay methodologies in a pediatric cohort from Mexico City, and to further examine associations with age and sex.
  
  
  METHODS
  Serum ANA were measured by indirect immunofluorescence assay (IFA) and multiplex immunoassay in 114 children aged 9-17 years. IFA was considered positive at a cutoff titer of ≥1:80. Agreement between assay methods was assessed by kappa statistic. Sensitivity, specificity, and 95% confidence intervals (CIs) of the multiplex were computed with IFA as the reference standard.
  
  
  RESULTS
  Of the 114 children (mean age 14.7 [standard deviation 2.1] years; 54 [47%] female), 18 of 114 (15.8%) were ANA positive by IFA, and 11 of 114 (9.6%) by 11-antigen multiplex assay. ANA prevalence was higher in females compared with males by both of the methods (ratios 1.6-1.9 to 1). Agreement between tests was classified as slight by kappa (κ=0.177 [95% CI -0.051, 0.406]). The multiplex immunoassay had sensitivity of 22.2% (95% CI 6.4, 47.6) and specificity of 92.7% (95% CI 85.6, 97.0), and failed to capture 3 of 4 (75%) of the high-titer (≥1:1280) IFA-positives.
  
  
  CONCLUSIONS
  Up to 15% of children in this general population cohort were ANA positive, with a higher rate of positivity among females according to both assay methods. Substantial discordance in ANA results was found between IFA and multiplex methods, even for high-titer IFA positives. These findings underscore the need to sufficiently account for assay characteristics when interpreting ANA test results, and support IFA as the more appropriate assay for studies of subclinical autoimmunity.
authors.affiliation: Divison of Rheumatology, Department of Internal Medicine; Department of Environmental Health Sciences; Department of Obstetrics & Gynecology.
authors.forename: Emily C
authors.initials: EC
authors.lastname: Somers
authors.affiliation: Divison of Rheumatology, Department of Internal Medicine.
authors.forename: Seetha U
authors.initials: SU
authors.lastname: Monrad
authors.affiliation: Division of Clinical Pathology, Department of Pathology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Warren
authors.affiliation: Center for Nutrition and Health Research, National Institute of Public Health, Cuernavaca, Morelos.
authors.forename: Maritsa
authors.initials: M
authors.lastname: Solano
authors.affiliation: Department of Developmental Neurobiology, National Institute of Perinatology, Mexico City, Mexico.
authors.forename: Lourdes
authors.initials: L
authors.lastname: Schnaas
authors.affiliation: Center for Nutrition and Health Research, National Institute of Public Health, Cuernavaca, Morelos.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Hernandez-Avila
authors.affiliation: Center for Nutrition and Health Research, National Institute of Public Health, Cuernavaca, Morelos.
authors.forename: Martha Maria
authors.initials: MM
authors.lastname: Tellez-Rojo
authors.affiliation: Occupational and Environmental Health, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
authors.forename: Howard
authors.initials: H
authors.lastname: Hu
keywords: autoantibodies; autoreactivity; biomarker; epidemiology; immune dysfunction; pediatric; preclinical; subclinical autoimmunity