Clinical utility of serum IgG4 measurement

•Elevated serum IgG4 may be seen in many conditions and is not specific to IgG4-related disease.•The specificity of serum IgG4 for diagnosing IgG4-RD increases with higher cut-off levels.•Elevated serum IgG4 manifests as a dense band on SPE, often with beta-gamma bridging.•Elevated IgG4 concentration on SPE may be mistaken for MGUS or elevated polyclonal IgA.•Method-specific limitations, gender and ethnic differences affect interpretation of serum IgG4.