Christine Bundell¹, Gabrielle Rule¹,Joanne Ong¹ and Anna Brusch^1
1 PathWest Laboratory Medicine

BACKGROUND: Inclusion body myositis (IBM) autoantibodies target cytosolic 5'-nucleotidase 1A (C5N1A). PathWest established an in-house ELISA based on details published by Greenburg et al (1) to assist in confirmation of an IBM diagnosis.  The ELISA measures IgG antibody bound to recombinant C5N1A antigen in patient serum. Serum from the Busselton Health Study and idiopathic inflammatory myopathy disease control groups was used to establish the reference value of 4.4RU.

METHOD: PathWest Immunology has been performing the C5N1A ELISA since 2018. The assay was initially reported as a research assay and later as a validated NATA accredited assay.  An audit of testing showed that samples are received from throughout Australia and New Zealand. 

RESULTS: From August 2020-September 2024 inclusive, 883 samples from 841 patients were tested, of these 51% were female.  Of the 159 positive individuals (19% of tested patients); 63% were female with a mean age of 61 years compared to 65 years for males.   

Clinical notes of antibody-positive WA patients show that 61.5% had a clinician confirmed diagnosis of IBM and one had likely IBM. 

CONCLUSION: The WA experience with C5N1A antibody positive patients is consistent with the published literature reporting C5N1A antibody positivity is not specific to IBM disease. 

REFERENCE:

1.            Greenberg SA. Cytoplasmic 5'-nucleotidase autoantibodies in inclusion body myositis: Isotypes and diagnostic utility. Muscle Nerve. 2014;50(4):488-92.

 

The work described in this abstract is a collective contribution from all the listed authors summarising a quality improvement audit for the laboratory.

 

AI was not used to prepare this abstract.