What is a DNA (Deoxyribonucleic Acid) (DS) Double-Stranded antibody blood test?

What is an Anti-dsDNA (Double-Stranded DNA) Antibody Blood Test?

An anti-dsDNA antibody blood test detects autoantibodies directed against double-stranded DNA in the blood, serving as the most prominent immunological criterion for diagnosing and monitoring systemic lupus erythematosus (SLE). 1

Purpose and Clinical Significance

The anti-dsDNA test is primarily used to:

• Diagnose SLE when combined with a positive ANA test (≥1:80 titer), as it constitutes a key classification criterion in the 2019 EULAR/ACR criteria 1, 2
• Monitor disease activity in established SLE patients, particularly for lupus nephritis, as antibody levels often correlate with active disease 3, 4
• Assess prognosis, since anti-dsDNA antibodies are associated with specific organ involvement including nephritis, skin manifestations, and neuropsychiatric disorders 1

Important Context About Anti-dsDNA Antibodies

Anti-dsDNA is not a uniform, SLE-specific entity but rather encompasses a heterogeneous group of antibodies with different antigenic specificities. 1 This is a critical misconception to avoid:

• These antibodies can be found in healthy individuals, other autoimmune syndromes, bacterial/viral/parasitic infections, and cancer 1
• They target multiple DNA structures including single-stranded DNA, left-handed dsDNA, right-handed dsDNA, RNA forms, bacterial DNA, and viral DNA 1
• The heterogeneity explains why different testing methods produce discordant results in the same patient 1

Testing Methodology

The recommended approach is a double-screening strategy using two complementary methods: 1, 5

First-Line Test: Solid-Phase Assay (SPA)

• Includes ELISA, FEIA (fluorescence enzyme immunoassay), or CLIA (chemiluminescence immunoassay) 1
• High sensitivity but lower specificity 1, 6
• Automated, quantitative, and rapid 4

Confirmatory Test: Crithidia luciliae Immunofluorescence Test (CLIFT)

• Uses the kinetoplast of Crithidia luciliae (a protozoan) as the DNA source 7
• Considered pathognomonic for SLE with very high specificity (98-100%) but low sensitivity (42-57%) 1, 7, 6
• Not automated, requires skilled interpretation 1

Result Interpretation Algorithm

The interpretation follows a hierarchical approach based on both test results: 5, 2

• SPA positive + CLIFT positive = SLE very likely 5, 2
• SPA positive + CLIFT negative = Evaluate in context of clinical characteristics; consider anti-nucleosome or antiphospholipid antibody testing 1, 5
• SPA negative + CLIFT positive = Inconsistent result requiring repeat testing in a new sample 1, 5
• SPA negative + CLIFT negative = SLE diagnosis cannot be established at this time 5, 2

Critical Prerequisites

A positive ANA test at titer ≥1:80 by indirect immunofluorescence on HEp-2 cells is the mandatory entry criterion before anti-dsDNA testing should be performed. 5, 2

• If ANA is negative, anti-dsDNA testing should not be ordered except in cases of very high clinical suspicion 1, 5
• This prevents unnecessary testing and false-positive results 2

Common Pitfalls to Avoid

Do not interpret a positive anti-dsDNA result in isolation without clinical context. 5, 3 Key mistakes include:

• Never initiate treatment based solely on positive anti-dsDNA without clinical evidence of active disease 5, 3
• Do not change laboratory methods between monitoring visits, as different assays use different antigens and scales, making serial comparisons invalid 5, 3
• Do not repeat ANA testing for monitoring once diagnosis is established—it is neither appropriate nor cost-effective 5, 3
• Remember that 30-40% of SLE patients may be anti-dsDNA negative, and some patients with lupus nephritis remain persistently negative 1, 3

Monitoring Protocol in Established SLE

For patients with confirmed SLE diagnosis:

• Measure anti-dsDNA antibodies quantitatively every 6-12 months using the same laboratory method 5, 3
• Always measure complement levels (C3, C4) alongside anti-dsDNA, even if previously normal 5, 3
• Rising anti-dsDNA titers with falling complement often indicate increasing disease activity, particularly renal involvement 3, 4

Laboratory Reporting Standards

Laboratories should 2:

• Specify which method was used (SPA type and/or CLIFT) 1, 2
• Report quantitative results in international units (IU) when available 2
• Provide clinical context beyond mere numbers, explaining the significance of results 2