West Nile Virus IgM Assays: ARUP Laboratorys experience

1
West Nile Virus IgM Assays ARUP Laboratorys
experience

• Christine M. Litwin, M.D.
• Associate Professor of Pathology,
• University of Utah
• Medical Director, Microbial Immunology
• ARUP Laboratories

2
History of WNV testing at ARUP

• 2001-2002 West Nile Virus Immunofluorescence
  assay (IFA) commercially available from PANBIO
  (ELISAs not yet commercially available)
• Compared well with CDCs IgM capture ELISA
• Agreement 98
• Sensitivity 96
• Specificity 100
• Am J Clin Pathol. 2003 Apr 119(4) 508-15.

3
History of Testing at ARUP

• 2003 Two commercial IgM-capture ELISAs
  available
• Focus TechnologiesWNV recombinant protein
• PANBIO inactivated purified native WNV antigen

4
Initial Evaluation of WNV IgM Commercial ELISAs

• Samples collected during 2002 outbreak
• Compared to IFA and CDC IgM-Capture ELISA

5
Initial Evaluation of WNV IgM Commercial ELISAs
6
West Nile Virus testingSpring 2003

• PANBIO IgM-capture test was selected
• Based on FDA approval of PANBIO Focus test was
  not yet approved by FDA
• Similar sensitivities and specificities between
  the two assays

7
Revalidation of the ELISAs Mid July 2003

• False positivity rate of PANBIO increased from
  1.9 to 6.6
• Initiated testing algorithm
• All samples initially screened positive with
  PANBIO were retested with Focus ELISA
• Out of a total of 1,924 samples tested by IgM
  PANBIO ELISA, 117 samples or 6.1 were false
  positive.

8
Revalidation of the ELISAs400 sera that were
consecutively submitted for WNV testing to ARUP,
were run in parallel with both the Focus and
PANBIO IgM ELISA
Focus IgM assay 10 of 59 positive samples were
false positive 16.9 PANBIO IgM assay 25 of 59
positive samples were false positive 34.2
9
Revalidation of the ELISAs
10
Focus Subtraction Procedure

• Focus Labs later instituted a Subtraction
  procedure, not initially described in the package
  insert protocol
• Index Value OD sample/ OD cutoff
• All Samples with OD 1.11are submitted to
  subtraction protocol
• Subtraction protocol
• OD sample -OD sample with no antigen Net OD
• If Net OD/ OD cutoff lt 1.1
• Then footnote is submitted stating that there is
  the presence of interfering antibody
• Suggest retesting in 7-10 days or retesting by
  another method. (IFA, PRNT)

11
ARUP West Nile Virus IgM antibody Testing with
subtraction validation

• Twenty samples that were positive by the Focus
  WNV IgM-capture ELISA
• screen were repeat tested using the Background
  Subtraction Procedure.
• Samples were then tested by the Utah Department
  of Health (UDOH)
• using the CDC-approved WNV testing procedure to
  confirm their results.

12
Acknowledgements June Pounder, Ph.D.
UDOH Annette Malan, B.S ARUP RD Pat
Stipanovich, MTASCP Supervisor, Microbial
Immunology, ARUP