Which laboratory tests are most useful in the initial evaluation of a patient with symptoms suggestive of a systemic autoimmune disorder?

In the initial evaluation of a patient presenting with symptoms suggestive of a systemic autoimmune disorder, the most useful laboratory tests include a full blood count (FBC) to assess for cytopenias, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to evaluate systemic inflammation, and autoantibody screening. Key autoantibodies to test for are antinuclear antibodies (ANA), which serve as a sensitive screening tool for systemic lupus erythematosus (SLE) and other connective tissue diseases, followed by more specific antibodies such as anti-double stranded DNA (anti-dsDNA) and extractable nuclear antigen (ENA) panel including anti-Ro, anti-La, anti-Sm, and anti-RNP antibodies to help confirm diagnosis and subtype the autoimmune disorder. Complement levels (C3, C4) are also valuable, particularly in suspected SLE, as low levels may indicate disease activity. Additionally, renal and liver function tests are important to assess organ involvement. These tests collectively provide a broad initial assessment to guide further specialist referral and management NICE NG95 Kurien & Scofield 2006Pramanik 2014Nikolopoulos et al. 2019.