A Simple Protocol for Identification of Heterophile Antibody by qvs59240

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									A Simple Protocol for Identification of
Heterophile Antibody Interferences in
   the Abbott AxSYM hCG Assay.

        P Giannopoulos, G Jones, E-M Lim
        Department of Chemical Pathology
          St Vincent’s Hospital, Sydney
     Heterophile Antibodies?

• Immunoglobulins found in some patient’s
  serum that bind antibodies from other
  species
• in 2 site immunoassays Heterophilic
  Antibodies can mimic the presence of
  analyte by binding the two antibodies in the
  assay
• produce false results
                   Why?

• Interference with Abbott AxSYM hCG
  assay
• Dr Laurence Cole, USA hCG Reference
  Laboratory
  – over 40 cases false positives
  – Average “hCG” 81 U/L
  – Laparoscopy, surgery, chemotherapy
• Consistent with heterophile antibodies
                 Abbott?

• Letter from Worldwide Marketing Manager
• January 2001
  – Urine hCG
  – Re-measure serum on alternate analyser
  – Identify clinical inconsistency
    Why are we telling you?



• RCPA AACB Quality Assurance Program
    -37% use AxSYM hCG assay
         How did we do it?

AxSYM:
      How do we do it now?

            Sydpath protocol

• hCG levels: 10 and 100U/L manual 1 in 2
• hCG levels: 100 and 1000U/L auto dilution
  1 in 10
• Dilution performed in hCG specific diluent
What is the Rationale for the
   Sydpath Protocol?


 •Increased amounts of animal proteins
    may block heterophile antibody
              interference
 Sample 52 uL




Diluent 11 uL
           What we found?


• 2400 hCG measurements
• 133 dilution protocol (5.6%)
• 2 patients with discrepant results on dilution
  (0.08%)
       Discrepant results?

• Patient A ?Pregnant
            hCG = 87 U/L (46-122)
            1 in 2 = 0 U/L

• Patient B ? Pregnant
            hCG = 83 U/L (52-121)
            1 in 2 = 0 U/L
        What we did next?

• Obtained urine samples
  – Negative on Hybritech Icon and AxSYM
• Measured serum on another analyser
  – hCG not detected
• Issued results: <2 U/L hCG
      Further Investigation?

• Other analysers
• Protein G agarose precipitation
• Serial dilution
Summary of Measurements

                 Patient A   Patient B
AxSYM (neat)        87          83
Bayer Centaur      ND          ND
Roche E170         ND          ND
Abbott i2000       ND          ND
DPC Immulite       ND           -
Hybritech Icon     Neg         Neg
        Protein G Agarose

              Ptn A     Ptn B Control
 hCG-pre        46       122       64
hCG-post         0        0        66



Protein G: An Immunoglobulin G binding protein
                 Dilutions in buffer

            60
            50
hCG (U/L)



            40
            30
            20
            10
             0
                 0   0.2    0.4     0.6    0.8   1
                              Dilution


                     Protein-free buffer
             Abbott Letter

• Discrepant results with clinical findings

• Urine HCG measurement

• Measure on another analyser
                 What we learnt?
    • The Abbott recommendation is limited for
      identifying false positive results.
    • SydPath Protocol: a fast, simple, cost-
      effective solution.
    • We prevented two incorrect results from
      being issued
    • Acknowledge Dr Laurence Cole.

These powerpoint slides will be available at
www.sydpath.stvincents.com.au after the conference.

								
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