title: Comparing Assay Performance of ELISA and Chemiluminescence Immunoassay in Detecting Antibodies to Hepatitis B Surface Antigen.
abstract: BACKGROUND
  Antibodies to Hepatitis B surface Antigen (Anti-HBs) levels are measured as markers for immune response to vaccination and in decision making for post-exposure prophylaxis against Hepatitis-B. Several immunoassay formats are used to measure Anti-HBs, thus carrying the possibility of variation in measured levels between different assays. This study compares the performance of Chemiluminescence Immunoassay (CLIA) against Enzyme-linked Immunosorbent Assay (ELISA) in measuring Anti-HBs titer by looking into concordance between the two test reports.
  
  
  OBJECTIVE
  To compare the agreement between ELISA and CLIA in measurement of Anti-HBs antibody titers.
  
  
  METHODS
  This prospective comparative study conducted at Kasturba Medical College, Manipal measured consecutive serum samples (69) sent for anti-HBs levels during May-June 2016 using both CLIA (Abbott Architect) and ELISA (Bio-Rad). Anti-HBs values of ≤10mIU/ml was considered as non-protective and >10mIU/ml as protective. The agreement between the tests in classifying the antibody titers as non-protective or protective was computed using Kappa coefficient, and the difference in individual titer values between the tests compared using Bland-Altman plot on SPSS (v.15).
  
  
  RESULTS
  Out of the 69 samples analysed, 18 samples (26.1%) were of health-care personnel and remaining of patients. Agreement between ELISA and CLIA in identifying the antibody titers as protective and non-protective were 96.5% and 90.9% respectively, resulting in an agreement of 0.84. The coefficient-of-variation of ELISA and CLIA were 74.5% and 113.1%, respectively. Three value based discordant results were noted; two samples deemed protective by ELISA were reported as non-protective by CLIA. One non-protective titer by ELISA was reported as protective by CLIA.
  
  
  CONCLUSIONS
  Analytical agreement is good between the two immunoassays. However there are some discrepancies in quantitative measurement. This may have been due the variation in the standard calibrators used in each assay. Though CLIA showed more variation in the values, it has the advantage of being automated test with low turn around time. Therefore, both the test methodologies can be reliably used in place of each other for detection of Anti- HBs titer.
authors.affiliation: Assistant Professor, Department of Microbiology, Kasturba Medical College, Manipal University , Manipal, Karnataka, India .
authors.forename: Mridula
authors.initials: M
authors.lastname: Madiyal
authors.affiliation: Tutor, Department of Microbiology, Kasturba Medical College, Manipal University , Manipal, Karnataka, India .
authors.forename: Siddharth
authors.initials: S
authors.lastname: Sagar
authors.affiliation: Associate Professor, Department of Microbiology, Kasturba Medical College, Manipal University , Manipal, Karnataka, India .
authors.forename: Shashidhar
authors.initials: S
authors.lastname: Vishwanath
authors.affiliation: Assistant Professor, Department of Microbiology, Kasturba Medical College, Manipal University , Manipal, Karnataka, India .
authors.forename: Barnini
authors.initials: B
authors.lastname: Banerjee
authors.affiliation: Professor, Department of Microbiology, Kasturba Medical College, Manipal University , Manipal, Karnataka, India .
authors.forename: Vandana Kalwaje
authors.initials: VK
authors.lastname: Eshwara
authors.affiliation: Professor and Head, Department of Microbiology, Kasturba Medical College, Manipal University , Manipal, Karnataka, India .
authors.forename: Kiran
authors.initials: K
authors.lastname: Chawla
keywords: Anti HBs titer; Bland-altman graph; Non-protective titer; Protective titer; Quantitative immunoassay