title: Diagnostic accuracy study of a factor VIII ELISA for detection of factor VIII antibodies in congenital and acquired haemophilia A.
abstract: Antibody formation to factor VIII (FVIII) remains the greatest clinical and diagnostic challenge to the haemophilia-treating physician. Current guidance for testing for inhibitory FVIII antibodies (inhibitors) recommends the functional Nijmegen-Bethesda assay (NBA). A FVIII ELISA offers a complementary, immunological approach for FVIII antibody testing. It was the aim of this study to retrospectively evaluate the performance of a FVIII ELISA (index) for detection of FVIII antibodies, compared with the NBA (reference). All samples sent for routine FVIII antibody testing at two haemophilia Comprehensive Care Centres, were tested in parallel using the NBA and a solid-phase, indirect FVIII ELISA kit (Immucor). A total of 497 samples from 239 patients (severe haemophilia A=140, non-severe haemophilia A=85, acquired haemophilia A=14) were available for analysis. Sixty-three samples tested positive by the NBA (prevalence 12.7%, 95% confidence interval [CI], 9.9-15.9 %), with a median inhibitor titre of 1.2 BU/ml (range 0.7-978.0). The FVIII ELISA demonstrated a specificity of 94.0% (95%CI, 91.3-96.0), sensitivity of 77.8% (95%CI, 65.5-87.3), negative predictive value of 96.7% (95%CI, 94.5-98.2), positive predictive value 65.3% (95%CI, 53.5-76.0), negative likelihood ratio 0.2 (95%CI, 0.1-0.4), positive likelihood ratio 13.0 (95%CI, 8.7-19.3) and a diagnostic odds ratio of 54.9 (95%CI, 27.0-112.0). Strong positive correlation (r=0.77, p<0.001) was seen between the results of the NBA (log adjusted) and FVIII ELISA optical density. In conclusion, FVIII ELISA offers a simple, specific, surveillance method enabling batch testing of non-urgent samples for the presence of FVIII antibodies.
authors.forename: Paul
authors.initials: P
authors.lastname: Batty
authors.forename: Gary W
authors.initials: GW
authors.lastname: Moore
authors.forename: Sean
authors.initials: S
authors.lastname: Platton
authors.forename: James C
authors.initials: JC
authors.lastname: Maloney
authors.forename: Ben
authors.initials: B
authors.lastname: Palmer
authors.forename: Louise
authors.initials: L
authors.lastname: Bowles
authors.forename: K John
authors.initials: KJ
authors.lastname: Pasi
authors.forename: Savita
authors.initials: S
authors.lastname: Rangarajan
authors.affiliation: Dr. Daniel Hart, Senior Clinical Lecturer and Honorary Consultant in Haemostasis, The Royal London Hospital Haemophilia Centre, The Royal London Hospital, London, E1 1BB, UK, Tel.: +44 203 594 1869, Fax: +44 203 594 1859, E-mail: daniel.hart@bartshealth.nhs.uk.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Hart
mesh_terms: D000704:Analysis of Variance; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D003029:Coagulants / Q000276:immunology* / Q000627:therapeutic use; D004797:Enzyme-Linked Immunosorbent Assay; D005169:Factor VIII / Q000276:immunology* / Q000627:therapeutic use; D006467:Hemophilia A / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics / Q000276:immunology; D006801:Humans; D016013:Likelihood Functions; D008131:London; D015588:Observer Variation; D016017:Odds Ratio; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012720:Severity of Illness Index
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D003029:Coagulants; D011933:Reagent Kits, Diagnostic; C078147:F8 protein, human; D005169:Factor VIII
keywords: Bethesda; ELISA; Factor VIII inhibitors; haemophilia A; sensitivity