What is ANA?
Anti-nuclear antigen. It is a test done to screen for inflammatory diseases such as lupus. 95% patients with lupus have ANA positive. It does not mean that if you have ANA positive you have lupus. This test can be positive in old age or if you have a close relative with an ‘autoimmune’ or inflammatory disease such as lupus, rheumatoid arthritis or thyroid disease. In any case the international protocol is for Rheumatologists to follow people with ANA positive for 2-years every 6-months to monitor for development of any autoimmune (inflammatory) disease.
ANA Subsets: These include antibodies to DNA (dsDNA), SS-A (Ro), SSB (La), RNP, Smith (Sm), Scl70, Jo-1.
These are all molecules in the cells against which antibodies develop because a hyperactive immune system is inappropriately exposed to them. This usually happens when the natural cell death, called apoptosis, does not execute properly.
E.g. Mutations in the gene TREX1, a major intracellular DNAse causing single-stranded DNA cleavage during apoptosis, lead to lupus (SLE) likely by inappropriately cleaving DNA and also resulting in dsDNA antibody formation.
General associations:
SLE (Lupus) is positive for ANA in 95% of cases
The remaining 4% is SSA positive
1% of lupus may be negative for all antibodies
SSA is associated with SLE and Sjogren’s
SSB is associated with Sjogren’s
RNP is present in MCTD (Mixed Connective Tissue Disease), SLE
Smith is associated with SLE and its kidney involvement
DNA is also associated with SLE and kidney involvement
Scl70 is associated with Scleroderma, SLE
JO-1 is associated with aggressive polymyositis
Again these are only associations. Presence of certain antibodies does not mean the patient has that disease, though it does make it somewhat more likely. Diagnosis is a clinical Rheumatology decision.