Anti Nuclear Antibodies (ELISA)

Function

Anti-Nuclear Antibodies (ANA) are a group of autoantibodies produced by the immune system that mistakenly target the nucleus of the body's own cells. The ELISA (Enzyme-Linked Immunosorbent Assay) method provides a quantitative or semi-quantitative screening to detect the presence of these antibodies in the blood. While the presence of ANA indicates immune system overactivity, it does not point to a specific disease without further testing.

Why it is Ordered

Physicians order an ANA test when a patient exhibits symptoms suggestive of a systemic autoimmune disorder. These symptoms may include:

• Persistent joint pain and swelling
• Unexplained fatigue and low-grade fever
• Butterfly-shaped skin rashes (malar rash)
• Muscle pain or sensitivity to light
• Raynaud’s phenomenon (fingers turning blue/white in the cold)

Associated Conditions

A positive ANA test is a hallmark of several connective tissue diseases, most notably:

1. Systemic Lupus Erythematosus (SLE): ANA is positive in about 95% of SLE cases.
2. Sjogren’s Syndrome: Causes dry eyes and dry mouth.
3. Scleroderma: Leads to hardening of skin and connective tissues.
4. Mixed Connective Tissue Disease (MCTD): An overlap of several conditions.
5. Autoimmune Hepatitis: A condition where the immune system attacks the liver.

It is important to note that ANA can also be positive in patients with chronic infections (like tuberculosis or endocarditis) or those taking certain medications (hydralazine, isoniazid). Furthermore, a small percentage of healthy individuals, particularly the elderly, may test positive for ANA without any underlying disease.