Diagnostic Markers in Autoimmune Diseases

Introduction to ANCA and dsDNA Antibodies

The American College of Rheumatology and European League Against Rheumatism recognize ANCA and dsDNA antibodies as important diagnostic markers for autoimmune diseases, with ANCA primarily associated with small vessel vasculitides and dsDNA being a key marker for systemic lupus erythematosus 1

c-ANCA (cytoplasmic pattern) primarily targets proteinase 3 (PR3) and is strongly associated with Wegener's granulomatosis (granulomatosis with polyangiitis) with 80-90% sensitivity 4
p-ANCA (perinuclear pattern) most commonly targets myeloperoxidase (MPO) and is associated with microscopic polyangiitis, pauci-immune crescentic glomerulonephritis, and eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome) 2
p-ANCA can also be found in autoimmune liver diseases (60-92% in primary sclerosing cholangitis), inflammatory bowel disease (60-87% in ulcerative colitis, 5-25% in Crohn's disease), and other autoimmune conditions 2

Anti-dsDNA antibodies are heterogeneous and can target various DNA structures, including single-stranded DNA (ssDNA), left-handed dsDNA (Z dsDNA), right-handed dsDNA (B dsDNA), and other nucleic acid structures 1, 5
They constitute the most prominent immunological criterion in the EULAR/ACR 2019 classification for SLE diagnosis 1
Anti-dsDNA antibodies can be detected using various methods including solid-phase assays (SPA) and Crithidia luciliae immunofluorescence test (CLIFT) 6
High specificity for SLE diagnosis, particularly when detected by CLIFT method 6
Strong association with lupus nephritis and other SLE manifestations including skin involvement and certain neuropsychiatric disorders 1
Useful for monitoring disease activity in SLE patients, with rising titers often correlating with disease flares 7

A positive ANCA or anti-dsDNA test alone is insufficient for diagnosis and must be interpreted in the clinical context 8
Different laboratories may use different methods and cutoffs, affecting result interpretation 8
False positives can occur in various conditions, including infections and malignancies 1
When suspecting SLE, a negative anti-dsDNA result does not rule out the disease, as some patients may be seronegative initially 6
For suspected SLE with positive ANA, if anti-dsDNA is positive by both SPA and CLIFT: SLE is very likely 6