Antinuclear Antibodies (ANA) - A Complete Guide

1. What is ANA?

• Disease-related: found in multiple conditions (e.g., basic ANA positivity)
• Disease-specific: highly associated with one particular disease (e.g., anti-dsDNA for SLE, anti-Scl-70 for systemic sclerosis)

Henry's Clinical Diagnosis and Management by Laboratory Methods - the detection and identification of ANA profiles has major diagnostic and prognostic implications.

2. Why Does the Body Make ANAs?

• Genetic predisposition (HLA genes, complement deficiencies)
• Environmental triggers (UV light, infections, drugs)
• Defective clearance of apoptotic material - when dying cells aren't cleaned up properly, nuclear debris becomes accessible to the immune system
• Molecular mimicry - immune responses against foreign antigens that cross-react with self-antigens

3. How is ANA Tested?

A. Indirect Immunofluorescence (IIF) on HEp-2 Cells - The Gold Standard

1. Patient serum is diluted serially (1:40, 1:80, 1:160, 1:320...) and placed on slides coated with HEp-2 cells (a human cancer cell line chosen because it has a high concentration of nuclear and cytoplasmic antigens)
2. If the patient has ANA, the antibodies bind to antigens in these cells
3. A fluorescent-tagged anti-human antibody is added - this lights up wherever the patient's antibodies have bound
4. A fluorescence microscope is used to visualize the staining pattern and measure the titer

Firestein & Kelley's Textbook of Rheumatology - IIF-ANA is a rapid yet highly sensitive screening method and remains the important standard for initial clinical testing.

B. Reporting Results: Titer and Pattern

• Negative: typically < 1:40
• Equivocal: 1:40 to 1:80
• Positive: > 1:80
• The 2019 EULAR/ACR classification criteria for SLE require an ANA titer ≥ 1:80 on HEp-2 cells as an entry criterion (sensitivity ~98%)
• Note: ~30% of healthy individuals are positive at 1:40, but only ~3% at 1:320 - so higher titers are more clinically meaningful

C. Other Detection Methods

Rheumatology (2022, Elsevier) - A 1:80 dilution is optimal for screening with the HEp-2 IIF method.

4. ANA Patterns - What They Mean

Nuclear Patterns

Cytoplasmic Patterns

Goldman-Cecil Medicine - the pattern of binding differs depending on the location of the macromolecular target; predominant patterns include homogeneous, rim, nucleolar, and speckled.

Anti-DFS70 - An Important "Negative" Marker

5. Specific ANA Subtypes and Their Clinical Significance

Anti-dsDNA (Anti-double-stranded DNA)

• Disease: Highly specific for SLE (~44-45% prevalence in SLE)
• Clinical use: Diagnosis + classification criterion for SLE; marker of disease activity and renal involvement (lupus nephritis)
• High-avidity anti-dsDNA + low complement = associated with lupus nephritis
• Titers can fluctuate with disease flares
• Testing: CLIFT (high specificity), ELISA, Farr RIA (reference)

Anti-Sm (Anti-Smith)

• Disease: Highly specific for SLE (though only ~6-11% prevalence)
• Named after patient Stephanie Smith, not the element
• Part of snRNP complexes involved in mRNA splicing

Anti-SSA/Ro and Anti-SSB/La

• Disease: Sjögren syndrome, SLE, neonatal lupus
• Anti-SSA/Ro prevalence in SLE: ~38-48%; in Sjögren: major criterion
• Neonatal lupus: Mothers with anti-SSA/Ro can pass antibodies to the fetus, causing:
  • Neonatal skin rash
  • Congenital complete heart block (anti-Ro52 is particularly associated)
  • The syndrome is transient (antibodies clear within months)
• Important: Anti-SSA can cause a false-negative IIF-ANA - a negative ANA does NOT exclude SSA/SSB antibodies

Anti-U1-RNP

• Disease: SLE, mixed connective tissue disease (MCTD) - high-titer anti-RNP is the defining feature of MCTD
• Part of U1 small nuclear ribonucleoprotein (snRNP) complex

Anti-Scl-70 (Anti-topoisomerase I)

• Disease: Diffuse cutaneous systemic sclerosis (dcSSc)
• Associated with interstitial lung disease (ILD)
• Yields a specific ANA pattern on IIF

Anti-centromere (ACA)

• Disease: Limited cutaneous SSc (lcSSc) / CREST syndrome
• CREST = Calcinosis, Raynaud, Esophageal dysmotility, Sclerodactyly, Telangiectasia
• More benign course compared to anti-Scl-70

Anti-RNA Polymerase III

• Disease: Diffuse SSc
• Associated with renal crisis in SSc and anti-cancer surveillance (may trigger paraneoplastic)

Anti-histone

• Disease: Drug-induced lupus (and also seen in SLE)
• Drugs causing drug-induced lupus: hydralazine, procainamide, isoniazid, phenytoin, penicillamine

Anti-Jo-1 and Myositis-Specific Antibodies (MSAs)

• Disease: Inflammatory myopathies (polymyositis, dermatomyositis)
• Anti-Jo-1 = anti-histidyl tRNA synthetase; associated with antisynthetase syndrome (ILD + myositis + mechanic's hands + fever)

Anti-Ribosomal P

• Disease: SLE - specific marker even though cytoplasmic in location
• Not a classification criterion but associated with lupus psychosis/cerebritis

6. ANA in Specific Diseases

Systemic Lupus Erythematosus (SLE)

• ANA sensitivity by IIF: >95% (92.3% in large SLICC study)
• Most common patterns: homogeneous and speckled
• Specific antibodies (prevalence):
  • Anti-dsDNA: 44-45%
  • Anti-Ro52: 38-41%
  • Anti-Ro60: 41-48%
  • Anti-SSB/La: 19-20%
  • Anti-Sm: 6-11%
  • Anti-U1RNP: 16-28%
  • Anti-ribosomal P: 9-11%
• Key fact: ANAs can precede clinical SLE by many years (US military cohort). Anti-dsDNA preceded diagnosis in 55% of patients.
• 2019 EULAR/ACR criteria require ANA ≥1:80 as an entry criterion

Sjögren Syndrome

• Anti-SSA/Ro + Anti-SSB/La are characteristic
• Anti-SSB alone (without SSA) is rare and has low diagnostic value
• Primary Sjögren: focal lymphocytic infiltration of exocrine glands

Systemic Sclerosis (SSc)

Mixed Connective Tissue Disease (MCTD)

• High-titer anti-U1-RNP is the defining serologic feature
• Overlapping features of SLE, SSc, and polymyositis

Juvenile Idiopathic Arthritis (JIA)

• ANA positive (IIF) in 40-85% of children with oligoarticular JIA
• Positive ANA is a strong risk factor for chronic anterior uveitis (can cause blindness)
• Early-onset ANA-positive JIA: requires age ≤6 years + two positive ANA tests (titer ≥1:160, ≥3 months apart)

Drug-Induced Lupus

• More than 75 drugs are associated, but only 5 regularly induce ANA: hydralazine, procainamide, isoniazid, phenytoin, penicillamine
• Anti-histone antibodies are characteristic
• Syndrome resolves when drug is stopped

7. Prevalence in Healthy People

• ~30% of healthy adults at 1:40 dilution
• ~5% of healthy adults at 1:160 dilution
• ~3% at 1:320 dilution
• More common in women
• Frequency increases with age
• Various non-rheumatic conditions: viral infections, thyroid disease, malignancy, chronic liver disease, some medications

Quick Compendium of Clinical Pathology - "Negative ANA virtually excludes SLE. Positive ANA is not specific for SLE."

8. Interpreting a Positive ANA - A Practical Approach

ANA positive on IIF (≥1:80)
        ↓
Ask: Does the patient have symptoms of CTD?
(fatigue, arthritis, rash, Raynaud, sicca, serositis, myositis)
        ↓ YES                           ↓ NO (isolated ANA)
Order specific antibodies:             Check for anti-DFS70
  - Anti-dsDNA                         If anti-DFS70 ONLY → likely benign
  - Anti-Sm
  - Anti-SSA/SSB
  - Anti-Scl-70
  - Anti-Jo-1
  - Anti-U1-RNP
  - Anti-centromere
        ↓
Correlate with clinical picture to diagnose specific SARD

9. False Positives and False Negatives

• Healthy individuals (especially elderly women)
• Infections (viral hepatitis, EBV, HIV)
• Thyroid disease (Hashimoto, Graves)
• Drug effect (even beyond the classic 5 drugs)
• Malignancy
• Fibromyalgia, chronic fatigue

• Some anti-SSA/Ro antibodies (especially anti-Ro60) can be negative by IIF
• Early disease
• Assay technical issues
• Some rare SLE patients (~5-8%) are truly ANA-negative

10. Summary Table of Key ANA Antibodies