Assay

Double-stranded DNA antibodies, (dsDNA)

Key Words

dsDNA IgG abs - (DNA), dsDNA abs (Crithidia Luciliae)- (CLDA)

Specimen Collection

Serum (brown)

Turnaround time

10 days

Test indications

Antibodies to double-stranded DNA (dsDNA) are seen in systemic lupus erythematosus (SLE) and to a lesser extent, in chronic active autoimmune hepatitis type I. A positive result for dsDNA antibodies supports the diagnosis of SLE. However only 60% of all patients with SLE have these antibodies in their serum and a negative test does not exclude the diagnosis.  Weak positives are found in other connective tissue diseases and in chronic and acute infection. To some extent, the antibody level in SLE patients indicates disease activity, but this should be gauged by clinical assessment, in combination with other markers such as complement C3, C4 values. Antibody levels against dsDNA may rise prior to a ‘flare’ of SLE and usually fall suddenly during the flare. Increases of >20% suggest a flare is imminent, and closer patient monitoring is recommended. In some individuals with SLE, dsDNA antibodies are always high, and in this case do not reflect disease activity. 

Samples positive for dsDNA are also tested using Crithidia as a substrate; samples which are Crithidia-positive contain high-affinity dsDNA antibodies, and are more closely linked to SLE; Crithidia-negative samples contain low-affinity antibodies and the association with SLE is poor. The Crithidia test is routinely performed on dsDNA-positive samples; there is no need to specifically request this test. All dsDNA antibody requests are screened for anti-nuclear antibodies; dsDNA testing is not routinely performed on ANA-negative samples.

Methodology

Enzyme immunoassay (all requests); Indirect immunofluorescence (Crithidia)

Interferences

No known methodological interferences

Reference Range

Negative  <10 IU/mL

Equivocal 10-15 IU/mL

Positive   >15 IU/mL

Analytical error

Contact the laboratory (x8454)

Reference change value

N/A