[The clinical immunology laboratory in diagnosis and monitoring of systemic lupus erythematosus and connective tissue diseases].

The laboratory and particularly clinical immunology laboratories have an essential role in diagnosing and monitoring systemic lupus erythematosus (SLE), as well as other connective tissue diseases. The role of the clinical immunology laboratory in these diseases is to confirm or exclude diagnosis, to monitor disease activity, and to identify subgroup of patients. To obtain the best results in terms of diagnostic performance and clinical usefulness, the following recommendations should be fulfilled: anti-nuclear antibodies (ANA) determination by indirect immunofluorescence on Hep-2 cells is an effective screening assay in patients with clinical features of SLE. A negative ANA test makes the diagnosis of SLE unlikely. Anti-dsDNA antibodies are highly specific for SLE and are associated with renal involvement. The method of choice for anti-dsDNA is the Farr assay; however, the necessity of using radioactive materials reduces its applicability. As an alternative, immunofluorescence on Crithidia Luciliae can be used in the diagnostic phase due to its high specificity. The detection of antibodies to extractable nuclear antigens (ENA) and to phospholipids (lupus anticoagulant and anti-cardiolipin antibodies) is useful in identifying subgroups of patients at risk for some clinical manifestations. Anti-dsDNA measurement with a quantitative assay (the Farr assay or ELISA) is currently the best method to monitor disease activity along with complement levels. New assays (anti-C1q and anti-nucleosome antibodies) have been recently proposed for the diagnosis (anti-nucleosome) and monitoring of SLE patients (anti-C1q and anti-nucleosome antibodies), with promising results.