investigations
Last reviewed 10/2023
- 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) (1)
- lupus anti-coagulant
- FBC
- normochromic normocytic anaemia
- haemolytic anaemia (in less than 15% - note that positive Coomb's test occurs in 65% of cases)
- leucopaenia - especially lymphocytopaenia
- 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 (1)
- 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.
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