ELISA in Diagnosing Infections and Autoimmune Diseases
ELISA serves as a valuable complementary diagnostic tool for detecting specific autoantibodies with known molecular targets in autoimmune diseases and for detecting pathogen-specific antibodies/antigens in infectious diseases, but it should not be used as the sole primary screening method for autoimmune conditions where indirect immunofluorescence (IIF) remains the gold standard. 1
Role in Autoimmune Disease Diagnosis
Primary Screening Limitations
The use of ELISA as the sole primary screening test for autoimmune-related autoantibodies is inappropriate because there is no useful combination of molecular specificities for dependable detection of ANA (anti-nuclear antibodies) and SMA (smooth muscle antibodies). 1 Indirect immunofluorescence on HEp-2 cells or rodent tissue sections remains the reference method for initial autoantibody screening. 1
Appropriate ELISA Applications in Autoimmunity
ELISA demonstrates excellent utility in specific autoimmune contexts:
For autoantibodies with identified molecular targets: ELISA based on recombinant/purified antigens (CYP2D6, FTCD, SLA/LP, F-actin) provides results interchangeable with IIF for anti-LKM1 and anti-LC1 antibodies in autoimmune hepatitis type 2. 1, 2
Anti-SLA/LP detection: Reliable commercial ELISA and dot-blot assays exist for detecting anti-soluble liver antigen antibodies, which are the only disease-specific autoantibody for autoimmune hepatitis with high diagnostic value. 1
Bullous pemphigoid: ELISA detects antibodies against BP180 and BP230, serving as a complementary diagnostic tool to immunofluorescence. 3, 2
SMA/anti-actin testing: While appropriate, IIF remains superior to ELISA and provides the best specificity/sensitivity compromise, as actin is not the only target antigen and ELISA can miss diagnosis in approximately 20% of cases. 1
Clinical Algorithm for Autoantibody Testing
The recommended approach follows this sequence 1:
- Initial screening: IIF on rodent tissue sections (liver, kidney, stomach) plus SLA/LP by ELISA or blot
- If positive: Assess pattern and titer (≥1:40 in adults; ≥1:20 for ANA/SMA or ≥1:10 for anti-LKM1 in children under 18 years) 1
- If initial tests negative but clinical suspicion remains: Repeat testing in specialty laboratory including specific immunoassays for LKM1, LC1, SLA/LP, F-actin, and atypical pANCA 1
Role in Infectious Disease Diagnosis
Broad Diagnostic Applications
ELISA demonstrates robust utility for infectious disease diagnosis:
HIV screening: ELISA is the initial test in the two-step diagnostic algorithm (ELISA followed by Western blot for confirmation). 2
Lyme disease: In endemic areas, ELISA serves as the first-line test, followed by Western blot to confirm positive or doubtful results. 2
Helicobacter pylori: ELISA detects antibodies against H. pylori, facilitating diagnosis of gastric infections. 3, 2
Invasive fungal infections: ELISA detects antigens such as galactomannan for aspergillosis or mannan/anti-mannan antibodies for candidiasis. 3, 2
Q fever and endocarditis: ELISA detects antibodies against Coxiella burnetii and other difficult-to-culture pathogens. 3, 2
Transplant screening: ELISA is used to detect anti-HLA antibodies in renal transplant candidates. 3, 2
Key Advantages
ELISA offers several practical benefits 2, 4, 5:
- High sensitivity and specificity when used correctly
- Simultaneous analysis of multiple samples (high-throughput capability)
- Rapid results without complex sample pre-processing
- Relatively inexpensive compared to other immunological techniques
- Commercial kits available with appropriate controls
- Portable versions enable point-of-care testing during outbreaks
Critical Limitations and Pitfalls
Interpretation Requirements
Results must always be interpreted within the clinical context and alongside other laboratory findings—never in isolation. 3, 2 The presence of autoantibodies by ELISA does not automatically establish disease diagnosis, as low titers do not exclude disease and high titers alone (without supportive findings) do not confirm it. 1
Technical Considerations
Cross-reactivity: Possible cross-reactions between related species can generate false positives. 3, 2
Standardization: Protocols must be standardized to ensure reliable results across laboratories. 3, 2
Quality control: Crucial to include positive and negative controls in every run to minimize false positives. 3, 2
Blocking steps: Necessary to prevent non-specific binding that can lead to false results. 3
Autoimmune-Specific Pitfalls
In autoimmune hepatitis specifically, ELISA misses approximately 20% of SMA-positive cases because multiple cytoskeletal elements beyond F-actin serve as targets. 1 Additionally, autoantibody titers in adults correlate only roughly with disease activity and treatment response, so serial monitoring is generally not recommended unless clinical phenotype changes significantly. 1
Practical Implementation
For infectious disease diagnosis, ELISA can serve as a standalone initial screening tool with appropriate confirmatory testing when indicated. 2, 5 For autoimmune disease diagnosis, ELISA should be positioned as a second-tier or confirmatory test after initial IIF screening, particularly for detecting autoantibodies with well-characterized molecular targets. 1, 2