The antibodies that cause a positive ana are called autoantibodies. White blood cells in the immune system make these to spot and attack foreign substances that cause infections or disease. But sometimes they can mistakenly target normal proteins in our bodies, and this can lead to inflammation that causes symptoms such as joint pains or skin rash. Everyone has small amounts of these, but if they are found in higher levels it can be a sign of an autoimmune disorder such as lupus, rheumatoid arthritis, scleroderma or Sjogren’s syndrome.
ANA is very sensitive for drug induced lupus and other autoimmune diseases such as systemic sclerosis/scleroderma, rheumatoid disease, discoid lupus, juvenile idiopathic arthritis, polyarteritis nodosa, giant cell arteritis and granulomatosis with polyangiitis (formerly Wegener’s granulomatosis). However, a negative ANA does not exclude these conditions completely and their diagnosis can't be based on a negative ANA alone.
Some studies have shown that cancer patients can have a positive ana but this is not well understood. It may be that these patients have a pre-autoimmune condition, such as anti-tubercular treatment, that was enough to trigger the appearance of ANAs. Others have found that certain types of cancer can affect the immune system, leading to an increased risk of autoimmune disorders such as SLE or RA. They may also have a defect in their innate and adaptive immune systems which can lead to poor clearance of apoptotic cells, microorganisms or tumours.