ANA Positive:
ANA (Anti Nuclear Antigen) is antibody against antigens of the nuclear material. The target nuclear antigen can be from any human cell or bacterial/viral/cancerous cells. Drugs and chemicals may have molecular mimicry with any nuclear antigen. So ANA can be positive in many conditions including autoimmune diseases, infections, drugs related, various immune diseases and even in 5-10% of healthy individuals. So positive ANA doesn’t mean SLE for everyone.
Also note that, as 5-10% cases of SLE are ANA negative, so it doesn’t exclude SLE in all the cases. However if ANA is negative it excludes SLE in 90-95% cases. Some of these ANA negative cases may later become ANA positive.
Titre of ANA positivity is imp. If it’s positive in high titres such 1:640 or more then it becomes more significant. If it’s weak positive such as 1:80 or 1:160 etc it is usually not significant.
ANA positivity in significant titres WITHOUT clinical symptoms or signs specific for any immune condition such as SLE doesn’t qualify for any treatment but just monitoring (for clinical signs and periodic lab tests such as 12-24 monthly). No need to get Rheumatology consult for such cases.
ANA isn’t routinely needed for lupus activity monitoring but we use Anti DsDNA and complements etc for this purpose.
Types & pattern of ANA or ENA is also important which will be discussed separately.
So important thing is these tests should only be ordered in cases where a specific autoimmune diagnosis such as SLE is strongly suspected. These are not routine blood tests and their interpretation is done based on clinical condition, not merely by the positive or negative result.