title: A new Eu(3+)-labeled method for anticardiolipin antibody IgM.
abstract: BACKGROUND
  The anticardiolipin antibodies (aCL) test has become a laboratory standard for the clinical diagnosis of antiphospholipid syndrome (APS). To better the quantitative detection of aCL-IgM so as to classify patients correctly and timely as APS positive, we established herein a new immunoassay based on a time-resolved fluoroimmunoassay (TRFIA).
  
  
  METHODS
  The complex of cardiolipin plus bovine anti-β2 glycoprotein-I was used as antigen fixed on microtiter plates to detect serum aCL-IgM, and Eu(3+) -labeled rabbit antihuman IgM was used as conjugate. The precision, sensitivity, specificity, coefficient of recovery, and stability of the assay were evaluated, and comparison with the traditional, classical enzyme-linked immunosorbent assay (ELISA) was also made.
  
  
  RESULTS
  The detection limit of the aCL-IgM TRFIA kit we established was 0.1 MPL U/ml, with a wider detectable range than commercial ELISA ones when a strong-positive specimen was diluted from 2,630.9 to 0.08 MPL U/ml. There was a good liner range within 0.16 to 2,630.9 MPL U/ml, whereas it was within 5.14 to 328.86 MPL U/ml when using three commercial ELISA ones. The average intra- and interassay variability was 3.19 and 3.70%, respectively. The mean recovery rate was 101.95%. The clinical diagnostic specificity was 98%. Additionally, the established assay kit presented good characteristics of stability and correlated well with the ELISA, and the correlation coefficient was 0.955.
  
  
  CONCLUSIONS
  The aCL-IgM TRFIA provides an approach to a more sensitive and reliable diagnosis of APS. Further validation of its use is required.
authors.affiliation: Department of Clinical Laboratory, Affiliated Wuxi People's Hospital of Nanjing Medical University, Wuxi, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Ye
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Hu
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Guoqian
authors.initials: G
authors.lastname: Chen
authors.forename: Yaohong
authors.initials: Y
authors.lastname: Zhou
mesh_terms: D000818:Animals; D017153:Antibodies, Anticardiolipin / Q000032:analysis*; D002138:Calibration; D002417:Cattle; D004797:Enzyme-Linked Immunosorbent Assay; D005063:Europium; D015200:Fluoroimmunoassay; D006801:Humans; D007075:Immunoglobulin M / Q000032:analysis*; D011933:Reagent Kits, Diagnostic; D012015:Reference Standards; D013194:Staining and Labeling
chemical_list: D017153:Antibodies, Anticardiolipin; D007075:Immunoglobulin M; D011933:Reagent Kits, Diagnostic; D005063:Europium
keywords: anticardiolipin antibodies; antiphospholipid syndrome; time-resolved fluoroimmunoassay