Serological Tests for Autoimmune Disease Diagnosis

Dermatomyositis (DM) and Polymyositis (PM)

For suspected inflammatory myopathies, order: creatine phosphokinase, myoglobin, aldolase, antisynthetase antibodies (Jo-1 and others if available), anti-MDA5, anti-Mi-2, anti-NXP2, anti-TIF1-γ, anti-SRP, anti-HMGCR, anti-SAE, anti-U1RNP, anti-PM/Scl75, anti-PM/Scl100, and anti-Ku 1
Myositis-specific antibodies are crucial for distinguishing between different forms of inflammatory myopathies 2
Immunoglobulin deposition (IgG, IgA, IgM) and C3 in muscle tissue can be observed in patients with overlapping Sjögren's syndrome and myositis 3

For suspected SLE, order: antinuclear antibody (ANA) by immunofluorescence assay (IIFA), anti-dsDNA antibodies, anti-Smith (Sm) antibodies, complement levels (C3, C4), anti-C1q antibodies (for lupus nephritis), and complete blood count 4, 5
Anti-Sm antibodies have high diagnostic specificity for SLE and produce a coarse speckled pattern on ANA testing 5
Anti-dsDNA antibody testing should be performed using either Crithidia luciliae immunofluorescence test (CLIFT) for high specificity or solid phase assays (SPA) for higher sensitivity 4

For suspected Sjögren's syndrome, order: anti-SSA/Ro antibodies, anti-SSB/La antibodies, ANA, rheumatoid factor (RF), salivary protein 1 (SP1), carbonic anhydrase 6 (CA6), and parotid secretory protein (PSP) 1
A point-of-care test is available that includes traditional serology as well as additional biomarkers (SP1, CA6, PSP) for Sjögren's syndrome 1
Anti-SSA/Ro and anti-SSB/La antibodies typically produce a fine speckled pattern on ANA testing 4

For suspected MCTD, order: ANA, anti-U1RNP antibodies (quantitative determination recommended), anti-Sm, anti-SSA/Ro, and anti-SSB/La 4, 6
Anti-U1RNP antibodies are the defining serological feature of MCTD and produce a coarse speckled pattern on ANA testing 4
MCTD often presents with overlapping features of multiple autoimmune diseases, requiring comprehensive antibody testing 6

For suspected systemic sclerosis, order: ANA, anti-Scl-70/topoisomerase-1, anti-centromere, anti-RNA polymerase III, anti-U1RNP, anti-Th/To, anti-PM/Scl, U3 RNP (fibrillarin), and anti-Ku 1
Anti-topoisomerase-1 (Scl-70) antibodies are associated with diffuse cutaneous systemic sclerosis 4
Anti-centromere antibodies are associated with limited cutaneous systemic sclerosis 4

For suspected Guillain-Barré syndrome, order: anti-ganglioside antibodies (GM1, GD1a, GD1b, GQ1b), and consider testing for recent infections (Campylobacter jejuni, cytomegalovirus, Epstein-Barr virus, and Zika virus) 1
Specific anti-ganglioside antibody patterns correlate with clinical variants of Guillain-Barré syndrome 1

For suspected IBM, order: creatine kinase, myoglobin, anti-cN1A (anti-NT5C1A) antibodies, and consider muscle biopsy for definitive diagnosis 2
IBM has characteristic rimmed vacuoles on muscle biopsy and often shows resistance to immunosuppressive therapy 2

For suspected NAM, order: creatine kinase, anti-SRP antibodies, anti-HMGCR antibodies, and consider statin medication history 2
NAM is characterized by myofiber necrosis without prominent inflammation on muscle biopsy 2

For suspected eosinophilic myositis, order: complete blood count with differential (to assess eosinophil count), creatine kinase, and consider testing for parasitic infections 1, 2

ANA testing by indirect immunofluorescence assay (IIFA) on HEp-2 cells is the reference method for initial screening, with a recommended screening dilution of 1:160 1
Different ANA patterns (homogeneous, speckled, nucleolar, etc.) suggest different autoantibodies and associated conditions 4
The method used for antibody detection should always be specified in the test result 1
In cases of high clinical suspicion, specific antibody testing should be performed regardless of ANA result 4
Results for specific extractable nuclear antigens (ENA) antibodies should be reported separately, including negative results 1

Not all positive ANA tests indicate autoimmune disease; up to 25% of healthy individuals can have positive ANA 1
Different testing methods may yield different results for the same antibody 7
Low-titer positive ANA results (1:40-1:80) should be interpreted with caution 4
Some autoantibodies may be present in ANA-negative patients 4
Autoantibody testing should only be performed in patients with reasonable clinical suspicion of autoimmune disease 7