Clinical Evaluation of ANA and anti-dsDNA Detection by Cobas Core Immunoassay Analyzer

Background : Detection of anti-nuclear antibody (ANA) is widely accepted as an important aid in the diagnosis of many connective tissue diseases. ANA testing by indirect immunofluorescent antibody (IFA) technique using HEp-2 cell as an antigen substrate is the preferred method, but time-consuming and subjective. Anti-dsDNA is specific for SLE and useful as follow-up monitoring of SLE patients. The gold standard of anti-dsDNA detection is Farr assay, but it is declining in importance due to Its considerable demands on laboratory time and costs incurred by the use of a radioactive substrate. To overcome these problems, enzyme immunoassay (EIA) has been developed and become available for routine use. In this study, we evaluated the newly developed Cobas Core EIA comparing to the IFA. Methods : From December 1997 to February 1998, we performed ANA and anti-DNA testing with 182 sera for ANA and 107 sera for anti-dsDNA. In all sera, we obtained concordant rates between FLUORO HEPANA TEST (MBL Co., LTD, Japan) and Cobas . Core HEp2 ANA EIA (Roche Diagnostic System, Switzerland), FLUORO nDNA TEST and Cobas Core Anti-dsDNA EIA. In sera with discordant results, we reviewed the clinical characteristics of the patients and compared with the results of EIA and IFA. In randomly selected 18 sera showing positivity by IFA, we performed Farr assay and compared it with EIA. Total imprecision CV of Cobas Core EIA was obtained by repeating the individual 5 sera with high, middle and low concentration of ANA and anti-dsDNA for 5 days, respectively. Results : Total imprecion CV was distributed from 0% to 7.8% in ANA and 0% to 7.9% In anti-dsDNA. The concordant rate between EIA and IFA was 88.5% in ANA and 80.4% in anti-dsDNA. The correlation coefficient (r value) between EIA and Farr assay was 0.95. Conclusions : Since Cobas Core EIA showed good correlation with IFA and is Possible for automation and random access, it is useful for screening a large number of clinical specimens as well as a small number of specimens. Further study with prospective design will be helpful for more accurate comparison between EIA and IFA.ope