Antinuclear antibodies: When to test and how to interpret findings

Dry eyes, dry mouth, joint pain and swelling, and swelling of parotid glands point to Sjögren’s syndrome. Anti-Ro/SS-A and La/SS-B antibodies are associated with Sjögren’s syndrome, but are also found in seronegative SLE.¹⁰ Therefore, if patients with features suggestive of SLE have a negative result on a dsDNA antibody assay, test for anti-Ro/SS-A and La/SS-B antibodies.

Muscle weakness and soreness, purplish discoloration of the upper eyelids, and purplish-red discoloration of the knuckles suggest dermatomyositis. Muscle biopsy and electromyography will clinch the diagnosis. Also test for anti–Jo-1 antibodies, which are associated with pulmonary involvement in polymyositis.¹¹

ANA’s continuing role—prognosis and disease activity

Besides confirming a diagnosis of CTD in patients with suggestive clinical features, ANA testing serves 2 additional purposes: to help determine a patient’s prognosis and to monitor CTD activity. Consider the following:

• Patients with Sjögren’s syndrome who test positive for anti-Ro/SS-A antibodies have aggressive, extra-glandular disease that can cause vasculitis, purpura, lymphadenopathy, leukopenia, and thrombocytopenia.¹²
• The presence of anti-Ro/SS-A in the circulation of pregnant women with SLE confers a higher risk of neonatal lupus erythematosus and of congenital heart block in their newborns.¹³
• Severe interstitial lung disease is frequently found in scleroderma patients who test positive for anti-Scl-70.¹⁴ Antibodies to aminoacyl-tRNA synthetases—including anti–Jo-1, as mentioned earlier—are associated with pulmonary involvement in polymyositis patients.¹¹
• A positive ANA test result in Raynaud’s phenomenon increases the likelihood that the patient will develop a systemic rheumatic disease; a negative result reduces this likelihood.¹⁵
• While the ANA test is not useful for diagnosing juvenile chronic arthritis (JCA), it is useful to test for ANA in patients with known JCA. A positive test result should prompt screening for uveitis.¹⁶
• An ANA test is not necessary for diagnosing antiphospholipid antibody syndrome (APS). However, the presence of ANA in a patient with APS increases the likelihood that APS is secondary to SLE.¹⁷

Monitoring disease activity

Documenting titers of anti-dsDNA antibodies may help in monitoring the disease activity of SLE in some patients. However, changes in titers of anti-dsDNA should be interpreted in the clinical context of the SLE Disease Activity Index.¹⁸

CORRESPONDENCE
Habib U. Rehman, MB, Department of Medicine, Regina Qu’Appelle Health Region, Regina General Hospital, 1440–14th Avenue, Regina, SK, S4P 0W5, Canada; habib31@sasktel.net