Immunology testing is relevant for the diagnosis of many autoimmune conditions. However, diagnostic pitfalls arise owing to incorrect interpretation of results and incomplete understanding of the underlying technique or immune-mediated condition. Here, we review the diagnostic considerations related to commonly used immunology tests. Specifically, we summarize the caveats pertinent to the interpretation of rheumatoid factor, antinuclear antibodies, antiphospholipid antibodies, antineutrophil cytoplasmic antibodies, and serum IgG4 testing.