A Real World Single Centre Experience Of Serum Igg4 Testing And Correlation With Clinical Outcomes

Introduction Immunoglobulin G4 related disease (IgG4-RD) is a rare, multi-system, fibroinflammatory condition that is increasingly recognised but proves a significant diagnostic challenge. In recent years more reliable diagnostic criteria based on clinical, biochemical, radiological and histological findings have set out to improve differentiating IgG4-RD from non IgG4-RD. Elevated serum IgG4 is not specific for the disease but is often the first investigation when there is suspicion of IgG4-RD. With the increasing use of serum IgG4, the aim of this study was to assess its real world utilisation and describe the diagnostic approach in those with raised levels in a non-specialist centre. Methods All measurements of serum IgG4 performed in a district general hospital in South Wales (UK) over 5 years were evaluated. In this retrospective observational study those individuals with raised levels were further analysed to assess demographics, clinical presentation, diagnostics and eventual diagnosis. In those with a diagnosis of IgG4-RD, both treatment and response were reviewed. Results 655 serum IgG4 measurements were performed on 560 patients. Of the 560 patients, serum IgG4 was raised (≥1.35 gl-1) in 81 (14.5%) and only 13 (2.3%) had a final diagnosis of IgG4-RD. In those with elevated serum IgG4 59 (72.8%) patients were tested for the purpose of differentiating IgG4-RD and non IgG4-RD. The median serum IgG4 in those diagnosed with IgG4-RD was 3.4 gl-1; this was 2.2 gl-1 in those with raised levels in non-IgG4-RD. Of the 13 patients diagnosed with IgG4-RD the majority had pancreatobiliary disease; 4 patients with pancreatitis and 3 with sclerosing cholangitis. 11 patients with IgG-RD were treated with corticosteroids at diagnosis with initial clinical response in all. Long term treatment included corticosteroids, azathioprine, methotrexate and mycophenolate with 3 patients on dual therapy. Conclusion Awareness of IgG4-RD is increasing and serological tests are requested with increasing frequency. However, only a small minority of patients found to have elevated serum IgG4 turn out to have IgG4-RD. The lack of specificity of raised serum IgG4 levels and the variable presentation of disease reinforce the importance of collecting data of patients found to have IgG4-RD. Given that not all cases of IgG4 RD have elevated levels, systematic review and clinical follow up of patients with suspected disease is necessary.