Anti-Double-Stranded DNA Antibody

Anti-double-stranded DNA (anti-dsDNA) antibodies are highly specific autoantibodies for systemic lupus erythematosus (SLE) (specificity 95 to 97%), present in 50 to 70% of patients. They react with native double stranded DNA and, through cross-reaction with nucleosomes and other antigens, are pathogenic in lupus nephritis, where they deposit in glomeruli and fix complement. Levels often rise before flares, especially renal flares, and fall with treatment, so the test is used for diagnosis, disease activity monitoring and prediction of nephritis.

Methods include the Crithidia luciliae immunofluorescence test (CLIFT), highly specific (low avidity antibodies are missed), ELISA, fluorescence enzyme immunoassay, chemiluminescence and the Farr radioimmunoassay (measures high avidity antibodies and correlates best with nephritis). SLE affects 20 to 150 in 100 000 people, with a female to male ratio of 9 to 1, higher incidence and severity in Black, Hispanic and Asian populations, and peak onset at 15 to 45 years. Lupus nephritis develops in 40 to 60% of patients and is the major determinant of outcome.

Indications. Positive ANA with a homogeneous or speckled pattern and clinical features of SLE (rash, arthritis, serositis, cytopenias, renal disease, neuropsychiatric symptoms). Monitoring SLE disease activity and response to treatment. Suspected lupus nephritis (proteinuria, haematuria, casts, rising creatinine). Prediction of flare in a quiet patient. Not for screening healthy people.

Specimen. Serum 1 mL, no fasting. Stable for several days at 2 to 8 °C. The same method is used for monitoring, because results are not comparable between assays.

Reference values (method dependent).

• ELISA: under 30 IU/mL (negative), 30 to 75 IU/mL (borderline or equivocal), over 75 IU/mL (positive). Some assays use under 10 IU/mL as negative.
• CLIFT: reported as a titre, with positive at 1 in 10 (low) up to 1 in 160 or higher (high).
• Farr assay: under 7 IU/mL.

Interpretation.

• Positive anti-dsDNA with typical clinical features: supports SLE, and is an immunological criterion in the classification of the disease.
• High titres (over 100 IU/mL or CLIFT 1 in 40 or more): associated with active disease, especially nephritis.
• Negative anti-dsDNA: does not exclude SLE (30 to 50% of patients are negative). Patients with anti-Ro, anti-Sm, antiphospholipid antibodies or ANA with other targets may be negative for dsDNA.
• Weak positives by ELISA with negative CLIFT occur in other conditions (autoimmune hepatitis, infections, other connective tissue diseases, drug induced lupus with anti-TNF drugs), so confirmation by a second method is done when the clinical picture is not typical.
• Rising titres with falling C3 and C4: predicts a flare, especially lupus nephritis, within weeks to months. Concordance is imperfect, and treatment is not based on a serological change alone in a clinically quiet patient, though close observation is needed.
• Falling titres after immunosuppression: response, though persistent positivity is common.
• Patients with persistently high anti-dsDNA, low complement and active urinary sediment: highest risk for nephritis.

Disease activity indices. Anti-dsDNA and complement are components of the SLEDAI score. The serological profile (high anti-dsDNA with low C3 and C4) correlates with renal and active disease.

Critical values and findings needing immediate action.

• Rising anti-dsDNA with low complement and new proteinuria, haematuria or raised creatinine: suspected lupus nephritis, urgent renal assessment and biopsy.
• High titre with neuropsychiatric features, serositis or cytopenias: severe SLE flare, urgent specialist review.
• Positive anti-dsDNA in pregnancy: increased risk of flare, pre-eclampsia and foetal loss, with close monitoring.
• Positive result in a patient on anti-TNF therapy: possible drug induced lupus, and the drug is reviewed.

Interferences and pitfalls.

• Method differences are large: ELISA is sensitive but less specific, CLIFT is specific but less sensitive, and the Farr assay correlates best with nephritis. The same method and laboratory are used to monitor.
• Positive anti-dsDNA is not specific for SLE when titres are low. It occurs in autoimmune hepatitis, rheumatoid arthritis, Sjögren syndrome, infections (viral hepatitis, Epstein-Barr virus), and with anti-TNF and interferon therapy.
• Anti-dsDNA can disappear in some patients with long standing, quiet SLE, and reappear before a flare.
• Clinical assessment, urinalysis and complement are needed alongside the antibody, since antibody levels alone do not decide treatment.
• Pregnancy and immunoglobulin therapy influence interpretation.
• Rheumatoid factor and heterophile antibodies can interfere with some immunoassays.
• A rising titre in a stable patient should prompt closer review but not automatic escalation.
• Anti-dsDNA does not distinguish activity of non-renal disease well.

Special groups.

• Children: SLE presents with more severe renal and haematological disease, and anti-dsDNA is raised in most.
• Pregnancy: anti-dsDNA, complement and urinary protein are monitored each trimester.
• Older adults: late onset SLE has milder renal disease and lower antibody frequency.
• Black and Asian patients: higher frequency of antibodies and nephritis.
• Regions: access to CLIFT or Farr assays is limited, and ELISA is used with confirmatory testing.

Follow up tests. ANA with pattern, extractable nuclear antigen panel, complement (C3, C4, CH50), antiphospholipid antibodies, full blood count, ESR and C-reactive protein, creatinine, urinalysis, urine protein to creatinine ratio, renal biopsy where nephritis is suspected, direct antiglobulin test, anti-C1q antibody, and anti-nucleosome antibodies.