Serology and International units

Transcription

1 Serology and International units L. Grangeot-Keros, National Reference Laboratory for Rubella, Virology Department, A. Béclère Hospital, Clamart, France

2 Detection of rubella-specific IgG antibody Assays Hemagglutination inhibition (HAI) Mainly enzyme and chemiluminescent assays Results IU/mL Identical results whatever the assay used

3 Quality control: results Past infection/ immunization For each QC, the same sample was tested with the assay used in the lab Assays Cut-off (IU/mL) Mean IU/mL QC1 QC2 QC3 Abbott Architect Abbott AxSYM Beckman Access/DXI DiaSorin Liaison Siemens Immulite Biomérieux Vidas Ortho Vitros Roche: Cobas 6000/Elecsys/Modular Siemens Advia Centaur 10 >

4 Quality control: results Assays Mean IU/mL Abbott Architect 46.9 Roche Cobas 6000/Elecsys/ Modular 383 International Standard used for calibration of Abbott Architect and Roche kits: RUBI st NIBSC international standard/ 3 rd WHO reference standard preparation

5 Quality control: results For each QC, the same sample was tested with the assay used in the lab Recent immunization Assays Cut-off (IU/mL) Mean IU/mL Abbott Architect Abbott AxSYM Beckman Access/DXI DiaSorin Liaison Siemens Immulite Biomérieux Vidas Ortho Vitros Roche: Cobas 6000/Elecsys/Modular Siemens Advia Centaur

6 Detection of rubella-specific IgG antibody Issues Depending on the assay used: Different cut-offs Different IgG results Different interpretations: immune/non immune

7 Cut-offs Sample no. HAI test result Access Cut-off: 15IU/mL Qual Quant IU/mL Result of immunoassay Immulite Cut-off: 10IU/mL Qual Quant IU/mL Vidas Cut-off: 15IU/mL Qual Quant IU/mL Equiv 13.8 Pos 15 Equiv Equiv 11.2 Pos 10,9 Equiv 11 From Dimech W et al. J Clin Microbiol. 2008; 46:

8 What cut-off should be chosen? 10 IU/mL? (recommended by the Rubella Subcommittee for Clinical Laboratory Standards) 15 IU/mL???????

9 Immunization of subjects with low levels of IgG antibody Studies Viremia/Virus excretion Type of immune response: primary vs secondary

10 Immunization of subjects with low levels of IgG antibody Antibody status before vaccination, Low titer (<15IU), in* No. of vaccinees No. with indicated finding Viremia Virus excretion Natural infection Previous vaccination Cendehill RA27/ HPV77-DE Unknown strain In*: intranasal challenge with RA27/3 rubella virus vaccine From O Shea S. et al. J Infect Dis 1983; 148: 639:647

11 Rubella-specific IgG IU/mL (mean value and 95% confidence intervals Matter L et al. J Infect Dis. 1997; 175: Immunization of subjects with low levels of IgG antibody Primary immune response (IgG+, IgM+) IgG IU/mL Secondary immune response (IgG +, IgM -) IgG < 15 IU/mL IgG IU/mL IgG IU/mL Before vaccination 1 3 months > 3 months

12 Immunization of subjects with low levels of IgG antibody Very often, when challenged with rubella vaccine, subjects with titers below the cutoff, nevertheless, show a secondary immune response

13 What cut-off should be chosen??????? It depends on the: Protection: complex phenomenon Quality of humoral immune response: - level of IgG - presence of neutralizing Ab - IgG avidity - other (IgG subclasses?) Quality of cell-mediated immunity?

14 What cut-off should be chosen? should the same cut-off be used for all assays?

15 What cut-off should be chosen? Toxoplasma-specific IgG assays Abbott Architect Assays Cut-off (IU/mL) 3 Abbott AxSYM 3 Beckman Access/DXI 10.5 Biomérieux Vidas 8 DiaSorin Liaison 8.8 Ortho Vitros 8 Roche Cobas 6000/Elecsys/Modular 30* Siemens Advia Centaur 10 Siemens Immulite 8 *: in France

16 Detection of rubella-specific IgG antibody Issues Depending on the assay used: Different IgG results

17 Quantitative IgG results Dimech W et al. J Clin Microbiol. 2008; 46:

18 Assays Quantitative IgG results Cut-off (IU/mL) no HAI 8* Access AxSYM Centaur > Enzygnost 10 < Immulite <5 Liaison Eti-Rubek plus Vidas *: reciprocal of the titer From Dimech W et al. J Clin Microbiol. 2008; 46:

19 Quantitative IgG results Quality control: the same sample was tested with the assay used in the lab Tests IgG Assays Cut-off IU/mL N Negative Equivocal Positive DIASORIN Liaison BECKMAN Access/DXI ABBOTT Architect ABBOTT AxSYM BIOMERIEUX Vidas ORTHOVitros ROCHE Cobas 6000/ Modular/Elecsys SIEMENS Advia Centaur SIEMENS Enzygnost SIEMENS Immulite TOTAL (%) (100) (10,07) (28,06) (61,87)

20 Seroconversion? Mrs. L. May 2009, 1 st pregnancy - rubella serology, June 30, laboratory A: < 10 IU/mL spontaneous abortion, July No vaccination In our lab : 10.5 IU/mL cutoff: 15 IU/mL 2 nd pregnancy, October rubella serology, November 2, laboratory B: 10 IU/mL - rubella serology, December 10, laboratory C: 224 IU/mL MMR: 23 Sep May 2000 In our lab: 11.7 IU/mL cutoff: 15 IU/mL

21 Different levels of IgG Ab: Why? Classic assays: - antigens: total virus - assay format: indirect assay "New generation assays: - antigens: recombinant virus, recombinant proteins - assay format: sandwich, competition or capture

22 Indirect ELISA Substrate E anti E anti E anti E anti IgM IgG Ag

23 ADVIA Centaur Rub G Capture immuno assay Incubation 18 minutes at 37 C Solid phase Anti-human IgG Fc monoclonal antibody coupled to magnetic particles Sample IgG antibody to rubella virus Lite reagent Inactivated rubella antigen (HPV 77 strain) labeled with acridinium ester Antigen-antibody complex Measurement of signal (RLUs)

24 Elecsys Rubella IgG Double sandwich

25 Is there any gold standard? HAI: lack of specificity (lipoproteins) lack of sensitivity Neutralization tests: labor intensive and time consuming Western-blot/Immunoblot : allows checking the specificity of the assay used

26 Western-blot control Sample no. Elecsys (cut-off 10 IU/ml) Access (cut-off 15 IU/ml) Cobas Core (cut-off 15 IU/ml) WB (anti-e1 protective antibody) Pos Pos Pos / Pos / Pos / Pos / Pos / Pos / Pos / Pos

27 Western-blot control - Since 2007, 178 serum samples were referred to our laboratory, because of discrepant results between Elecsys rubella IgG assay (Roche) and another assay (Elecsys : pos / other assay: neg). - Specificity controlled on 137 samples, by using an in-house Western-blot (sensitivity: 3-5 IU/mL). - Anti-E1 Rubella antibodies detected in 133/137 (97%) samples Discrepancies largely due to higher sensitivity

28 Detection of rubella-specific IgG antibody Conclusion Remaining questions Is it sound to report results in International Units? Should all assays use the same cut-off? Can a protective cut-off be determined? Depending on the situation, - rubella antibody screening during pregnancy, or - epidemiological (seroprevalence) studies should equivocal results be interpreted in the same way?

29 Many thanks to Christelle Vauloup-Fellous Marlène Guillet