Anti-Nuclear Antibodies (ANA) - Exam Notes (MD Dermatology)

1. Definition

• Characteristically associated with connective tissue diseases (CTDs)
• Can also be seen in non-rheumatic conditions and in the healthy general population

2. History (quick recall points)

• LE cell phenomenon - described by Hargraves, Richmond, Morton (1948)
• Original substrate: kidney/liver sections of rats/mice
• Now replaced by HEp-2 cells (Human Epithelial type-2) - larger nuclei allow easier pattern recognition

3. Methods of ANA Detection

A. Indirect Immunofluorescence Antibody technique (IFA) / FANA (Fluorescent ANA)

• Gold standard / method of choice (per ACR ANA Task Force, 2009)
• Serum/plasma incubated with HEp-2 cell substrate fixed on a slide
• Serial dilutions done to get an endpoint titer
• Three parameters reported: pattern of fluorescence, substrate used, titer

1. Detects a large number of autoantibodies (large HEp-2 nuclei)
2. High sensitivity - 95-100% for SLE
3. Pattern gives diagnostic clue

1. Low specificity (~43% at 1:40, ~63% at 1:80 dilution)
2. Affected by variables - reagent quality, substrate, conjugate, microscope bulb, reader
3. HEp-2 cells may lack some antigens (e.g., Ro-60, ribosomal-P) - false negatives
4. Labor and skill intensive

B. Solid-phase assays

1. ELISA
2. Immunoblot assay
3. Line immunoassay
4. Chemiluminescence immunoassay
5. Multiplex bead-based assay
6. Chip-based assay

1. Low sensitivity (69-98%, average 87%) - less suitable for screening
2. Many HEp-2 antigens absent from solid-phase substrate -> higher false-negative rate

Exam tip: IFA = high sensitivity/low specificity (best screening test); Solid-phase = lower sensitivity but more specific antigen identification.

4. ANA Titer Interpretation

• Titer = the last dilution at which fluorescence is still positive (quantitative expression of ANA concentration)
• No universal consensus on screening dilution, but 1:160 is generally taken as significant (some experts suggest lower titers)
• Staining intensity graded qualitatively + to ++++ - considered proportional to antibody concentration and may reflect disease severity, though not diagnostic on its own

5. Staining Patterns (High-yield table)

Pattern-Antigen-Disease Correlation (must-know table)

Note: Staining pattern gives a clue to underlying CTD but is not specific/diagnostic by itself.

6. ANA Profile

• A panel of individual autoantibody tests offered along with/instead of FANA
• Usually includes: anti-ssDNA, anti-dsDNA, RNP, Ro, La, Sm, topoisomerase I (Scl-70)
• Higher sensitivity than FANA alone; gives additional diagnostic/prognostic value
• Caveat: technique varies between labs -> inconsistent performance

7. When TO Test for ANA

• Only when there is clinical suspicion of an autoimmune CTD
• If ANA positive -> order specific autoantibody tests based on clinical picture
• If ANA negative but clinical suspicion is high -> re-evaluate, follow up, repeat only if clinically indicated
• If still negative with strong SLE suspicion -> check anti-SSA (Ro) antibody (helps diagnose ANA-negative SLE)

8. When NOT to Test for ANA (frequently asked)

1. To confirm rheumatoid arthritis or osteoarthritis
2. To evaluate isolated fatigue, back pain, or musculoskeletal pain without other CTD features
3. Screening of asymptomatic individuals
4. Not for monitoring disease activity - titer changes are not clinically useful for follow-up
5. Repeat negative test only if strong suspicion of evolving CTD or change in clinical picture

9. Fallacies / Pitfalls of ANA Testing

• Rheumatic disease is uncommon in the general population, but ANA positivity by IFA can be high in healthy people
• Most ANA-positive people never develop rheumatic disease
• Test utility depends on pre-test probability - higher pre-test probability -> more useful test
• Indiscriminate screening -> ~5% false positivity at standard screening dilution (1:160)
• A positive ANA/SLE diagnosis should NOT lead to attributing every clinical feature to SLE -> Greenwald's law of lupus
• However, screening may identify a "pre-autoimmunity" state (autoreactivity before clinical disease manifests) in select at-risk groups

10. Non-CTD Causes of Positive ANA (Table 3 - important for exam)

11. ANA-Negative Lupus

• Prevalence: 5-10% of lupus cases
• Causes:
  1. Antigen-deficient substrate / leaching of antigens
  2. Concurrent immunosuppressive treatment
  3. Persistent renal protein loss
  4. False diagnosis of lupus

12. Which Test to Order First?

• ACR ANA Task Force (2009): IFA remains gold standard due to high sensitivity (>95%)

13. Conclusion (exam one-liner)

Quick Revision Points for Viva/Theory

• IFA on HEp-2 cells = gold standard, most sensitive (95-100% for SLE)
• Screening dilution: 1:160 significant
• 3 parameters reported in IFA: pattern, substrate, titer
• Homogeneous pattern -> dsDNA/histones -> SLE
• Speckled -> ENA/Sm/Ro/La -> SLE, MCTD, Sjogren's, systemic sclerosis
• Nucleolar -> systemic sclerosis
• Centromere -> limited cutaneous systemic sclerosis (CREST)
• ANA not for screening asymptomatic people, not for monitoring disease activity
• Greenwald's law of lupus - don't attribute all symptoms to SLE just because ANA/SLE positive
• ANA-negative lupus: 5-10%, check anti-Ro/SSA if suspicion persists