Investigations

• serology
  • autoantibodies
  • antinuclear antibodies (ANA) - seen in 98% of patients
    • the specificity is low since ANAs are found in many other conditions such as scleroderma, polymyositis, dermatomyositis, rheumatoid arthritis
  • anti-double-stranded DNA (dsDNA) - highly specific for SLE, only present in around 70% of patients
  • other autoantibodies include - anti-Smith, anti-ribosomal P and anti-proliferating cell nuclear antigen (PCNA)
  • lupus anti-coagulant
• FBC
  • normochromic normocytic anaemia
  • haemolytic anaemia (in less than 15% - note that positive Coomb's test occurs in 65% of cases)
  • leucopenia - especially lymphocytopenia
  • thrombocytopaenia
• polyclonal hypergammaglobulinaemia
• ESR
  • usually raised
  • not always reliable but changes may correlate well with disease activity
• CRP
  • usually do not increase unless there is arthritis or serositis
  • consider infection if increased
• reduced serum complement concentrations -
  • usually, firstly of C4, then C3, C1q and total haemolytic complement activity (CH50)
  • thought to result from complement consumption by immune complexes

Tests may be performed for specific clinical manifestations for example, renal function tests; tissue biopsy of skin, kidney, lymph nodes; examination of synovial fluid.

Reference:

1. Gordon C, Amissah-Arthur MB, Gayed M, et al. The British Society for Rheumatology guideline for the management of systemic lupus erythematosus in adults. Rheumatology (Oxford). 2017 Oct 6.