Indications for Testing
The following SARDs may manifest with these indications :
- SLE: rash, photosensitivity, oral ulcers, polyarticular arthritis, proteinurea or cellular casts, pleuritis, pericarditis, interstitial nephritis, fatigue, cytopenia, seizures or psychosis
- Sjögren syndrome: dry mouth, dry eyes
- Mixed or undifferentiated connective tissue disease: Raynaud syndrome, joint aches, puffy fingers, low-grade myositis
- Systemic sclerosis: Raynaud syndrome, sclerodactyly, interstitial lung disease/pulmonary hypertension, gastroesophageal reflux
- Inflammatory myopathies (including polymyositis, dermatomyositis, and necrotizing autoimmune myopathies): progressive muscle weakness (usually proximal), with or without rashes
Laboratory Testing
Diagnosis
ANA Testing
A starting point for testing for SARDs is ANA testing. Antibodies in SARDs can target the nucleus as well as any intracellular components of the cell, most notably the cytoplasm. ANA tests are best used for individuals with a high pretest probability of having a SARD, as ANA reactivity may be present in healthy patients as well as those with certain infections, cancer, and autoimmune diseases.
The gold standard for ANA testing is the indirect fluorescent antibody (IFA) assay, performed in a lab experienced with ANA testing. ANA test interpretation is based on common ANA patterns that have shown consistent correlation with SARDs. Patterns reported by ARUP Laboratories include homogeneous, speckled, centromere, nucleolar, nuclear dots, or cytoplasmic (see table below). The International Consensus on ANA Patterns has comprehensive information on patterns, targets, and clinical associations. ANA IFA reports should include the method, type of substrate, results obtained (including qualitative response [positive or negative]), pattern(s) observed, and their titers.
In cases of high clinical suspicion for SARDs, specific autoantibody testing should be performed, even if ANA testing is negative.
ANA Patterns, Autoantibody Targets, and Clinical Associations
| Patterns |
Primary Autoantibody Targets |
Clinical Associations |
|---|
| Centromere |
Centromere A/B(C) |
SSc, PBC |
| Homogeneous |
dsDNA, histones or chromatin (nucleosomes) |
SLE, drug-induced SLE or JIA |
| Nuclear dots |
NXP-2, Sp100 |
PBC, DM, SjS, SLE, SSc, PM/td> |
| Nucleolar |
PM/Scl, RNA polymerase, URNP, U3-RNP (fibrillarin), Th/To, NOR-90 |
SSc, SSc/PM overlap, SjS |
| Speckled |
SSA-52 (Ro52), SSA-60 (Ro60), SSB/LA, Topo-1 (Scl-70), Smith, U1-RNP, U2-RNP, Mi-2, TIF1g, Ku, RNA polymerase, DFS70/LEDGF-P75 |
SLE, SSc, SjS, DM, PM, MCTD, UCTD (may also be found in healthy individuals) |
| Cytoplasmic |
Ribosomal P, tRNA synthetase (Jo-1, PL-7, PL-12, EJ, OJ), SRP or mitochondria (AMA) |
ARS, ILD, IM,a SLE, SSc, SjS, RA, MCTD, PBC, AIH, infectious, neurologic, and other inflammatory conditions |
|
| aIM includes DM, PM, and NAM
AIH, autoimmune hepatitis; ARS, antisynthetase syndrome; DM, dermatomyositis; ILD, interstitial lung disease; IM, inflammatory myopathies; JIA, juvenile idiopathic arthritis; MCTD, mixed connective tissue disease; NAM, necrotizing autoimmune myopathy; PBC, primary biliary cholangitis; PM, polymyositis; RA, rheumatoid arthritis; SjS, Sjögren syndrome; SRP, signal recognition particle; SSc, systemic sclerosis; UCTD, undifferentiated connective tissue disease
Sources: Tebo, 2017 ; Agmon-Levin, 2014
|
In addition to IFA ANA testing, other testing options are available. See table below for comparison of ANA testing methods.
Comparison of ANA Testing Methods
| Method |
Advantages |
Disadvantages |
|---|
| IFA |
Preferred method
Strong screening tool; resulting patterns can guide confirmatory testing for specific diagnosis or prognosis
|
Labor intensive
Subjective (in titer and pattern recognition)
Reagents not well standardized
Has limited diagnostic specificity
Requires significant expertise to interpret
Appropriate cutoff value for positivity not established
|
| ELISA |
Commonly available
Specificities for CTDs may be affected by limited antigenic targets
Has lower sensitivity than IFA
Offers faster TAT
More objective than IFA
High throughput
|
Has lower sensitivity than IFA
Clinical performances of commercial ELISAs vary
May not be useful in assessing ALDs or SARDs that target complex autoantigens
|
| CLIA |
More sensitive than ELISA
Easier to automate than ELISA
Wide analytical measurement range (vs ELISA)
Offers faster TAT
More objective than IFA
High throughput
|
May not be useful in assessing autoimmune liver diseases or SARDs that target complex autoantigens
Has lower sensitivity than IFA
|
| Multiplex assay (LIA, MBA) |
Can detect multiple independent antibodies associated with ANAs
Can be automated
Can provide quantitative or qualitative results
Faster TAT
More objective than IFA
High throughput
Useful in analyzing autoantibody clusters and evaluating diseases with multiple autoantibody specificities (vs. ELISA)
|
Has lower sensitivity than IFA
Diagnostic accuracies differ among immunoassays
LIA is not as technologically sophisticated as MBA
|
| ALDs, autoimmune liver diseases; CLIA, chemiluminescence immunoassay; ELISA, enzyme-linked immunosorbent assay; LIA, line immunoassay; MBA, multiplexed bead assay; TAT, turnaround time
Source: Tebo, 2017
|
Monitoring
Once a SARD has been diagnosed, monitoring tests should be based on organ involvement. If cytopenias are present, the patient should be monitored with sequential CBCs. Certain treatment drugs require testing for liver function. In addition, patients should be monitored for malignancy. Dermatomyositis and mixed connective tissue disease have shown increased risk for malignancy, and Sjögren syndrome is associated with an increased risk for hematologic malignancy, specifically.
