The diagnostic utility of IgG index and oligoclonal bands for multiple sclerosis in a neurology hospital patient population.

Background: Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system. Diagnosis is based on the 2017 revised McDonald criteria. Unmatched oligoclonal bands (OCB) within the CSF (i.e. positive OCB) can substitute for dissemination in time by magnetic resonance imaging (MRI). Simonsen et al. (2020) claimed a raised (>0.7) immunoglobulin G (IgG) index could replace OCB status. This study aimed to establish the diagnostic utility of IgG index for MS in the population served by The Walton Centre NHS Foundation Trust (WCFT) a neurology and neurosurgery hospital, and to derive a population-based IgG index reference interval.

Methods: OCB results from the laboratory information system (LIS) were collated from November 2018 to 2021. Final diagnosis and medication history was obtained from the electronic patient record. Exclusions were made based on age (<18 years) at the time of lumbar puncture (LP) disease-modifying treatment prior to LP, unknown IgG index and unclear OCB patterns.

Results: 935 of 1101 results remained following exclusions. 226 (24.2%) had a diagnosis of MS, 212 (93.8%) were OCB positive and 165 (73.0%) had a raised IgG index. The diagnostic specificity of a raised IgG index was calculated at 90.3% compared to 86.9% for positive OCB. 386 results with negative OCB were used to establish the IgG index reference interval (0.36-0.68) at 95th percentiles.

Conclusion: This study provides evidence that IgG index should not replace OCB in the diagnosis of MS. >0.7 is an appropriate cut-off to define a raised IgG index for the patient population.