What tests should be ordered to screen for Limited Systemic Sclerosis (CREST), Systemic Lupus Erythematosus (SLE), Mixed Connective Tissue Disease (MCTD), Rheumatoid Arthritis (RA), Polymyositis (PM), and Sjogren's syndrome?

Serologic Screening for Connective Tissue Diseases

Order an antinuclear antibody (ANA) test by indirect immunofluorescence as the initial screening test for all suspected connective tissue diseases, followed by disease-specific autoantibody panels based on clinical presentation and ANA pattern. 1, 2, 3

Initial Screening Test

• ANA by indirect immunofluorescence is the recommended first-line screening test for CREST (limited systemic sclerosis), SLE, MCTD, Sjogren's, and polymyositis 1, 2, 4
• The ANA pattern (homogeneous, speckled, nucleolar, centromere) provides critical clues to guide subsequent specific autoantibody testing 1
• ANA testing alone is insufficient for diagnosis—it is nonspecific and requires confirmatory disease-specific antibodies 4, 3

Disease-Specific Autoantibody Panels

For Systemic Sclerosis/CREST Syndrome

• Anti-topoisomerase I (anti-Scl-70): Associated with diffuse cutaneous disease and interstitial lung disease 1, 2
• Anti-centromere antibody: Strongly associated with limited cutaneous systemic sclerosis (CREST syndrome) and primary biliary cholangitis 2, 4
• Anti-RNA polymerase III: Associated with diffuse disease, rapid progression, scleroderma renal crisis, and increased malignancy risk 1, 2
• Anti-U3RNP (fibrillarin): Associated with diffuse scleroderma and pulmonary arterial hypertension 2

For Systemic Lupus Erythematosus

• Anti-double stranded DNA (anti-dsDNA): Highly specific for SLE and useful for monitoring disease activity 4, 3
• Anti-Smith antibody: Highly specific for SLE 5, 3
• Anti-histone antibody: Associated with drug-induced lupus 4
• Anti-Ro (SSA) and anti-La (SSB): Present in SLE and associated with neonatal lupus 4, 3

For Mixed Connective Tissue Disease

• Anti-U1RNP antibody: Defining antibody for MCTD, suggests overlap syndrome 1, 2, 3
• High titers of anti-U1RNP at baseline predict ILD progression 6

For Rheumatoid Arthritis

• Rheumatoid factor (RF): Supports diagnosis but is nonspecific; high titers associated with progressive disease and erosions 4, 3
• Anti-cyclic citrullinated peptide (anti-CCP) antibody: More specific than RF for RA diagnosis; high titers increase risk of interstitial lung disease 6, 3

For Polymyositis

• Myositis-specific antibodies (MSAs): Anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, anti-OJ, anti-KS, anti-Ha, anti-Zo (anti-synthetase antibodies) 6, 7
• Anti-MDA-5: Associated with rapidly progressive ILD 6
• Anti-Ku and anti-PM/Scl: Associated with myositis-scleroderma overlap 6, 7
• Anti-Ro52: Associated with ILD risk 6

For Sjögren's Syndrome

• Anti-SSA/Ro and anti-SSB/La antibodies: Characteristic of Sjögren's syndrome 6, 3
• Anti-Ro52: Associated with increased ILD risk 6
• Rheumatoid factor: May be positive in Sjögren's syndrome 6, 3

Additional Supporting Laboratory Tests

• Complete blood count: Screen for cytopenias (SLE, Sjögren's) and lymphopenia (Sjögren's with ILD risk) 1, 5
• Comprehensive metabolic panel: Assess kidney and liver function 1
• Inflammatory markers (ESR, CRP): Assess disease activity, particularly in RA and overlap syndromes 2, 4
• Creatine kinase (CK): Elevated in polymyositis/dermatomyositis 7

Practical Testing Algorithm

1. Start with ANA by immunofluorescence in all patients with suspected connective tissue disease 1, 2
2. If ANA positive with nucleolar pattern: Order anti-Scl-70, anti-centromere, anti-RNA polymerase III, anti-U3RNP 1, 2
3. If ANA positive with homogeneous/speckled pattern: Order anti-dsDNA, anti-Smith, anti-Ro, anti-La, anti-U1RNP 5, 4, 3
4. If clinical features suggest myositis: Order myositis-specific antibody panel (anti-synthetase antibodies, anti-MDA-5, anti-Ku, anti-PM/Scl, anti-Ro52) regardless of ANA result 6, 7
5. If clinical features suggest RA: Order RF and anti-CCP antibody 4, 3
6. If clinical features suggest Sjögren's: Order anti-SSA/Ro, anti-SSB/La, and RF 6, 3

Critical Caveats

• Up to 40% of patients with idiopathic pulmonary arterial hypertension have elevated ANA without connective tissue disease—positive ANA requires clinical correlation 2
• Overlap syndromes are common, with patients meeting criteria for multiple connective tissue diseases simultaneously; comprehensive autoantibody panels may be necessary 8, 7
• MSAs and myositis-associated antibodies are mutually exclusive and present in only 38.8% of overlap syndrome patients 7
• Seronegative disease exists for all conditions—negative antibodies do not exclude diagnosis when clinical features are compelling 4, 3
• Order serologic tests only when pretest probability is high based on clinical features; indiscriminate screening leads to false positives 3