What could cause a positive ana titre of 1:320? also hilar and mediasternal lymphadenopathy? possibly related to each other?

Autoimmune: 1:320 is a high titre of ANA, so likely positive for an autoimmune disorder. The diagnosis is made from multiple factors, so that test alone is not diagnostic of any specific disorder. Adding the hilar and mediastinal lymphadenopathy makes Sarcoidosis more likely, though there are many other causes of each finding. Your PCP may want to send you to a rheumatologist.

My recommendation: 1. ANA, can be nonspecific. Positive usually reflect an autoimmune process such autoimmune hepatitis or SLE, etc. With titer of 1:320, I recommend you see a rheumatologist for further work-up. 2. Hilar and mediastinopathies are concerning. If CT report does raise a concern, you should see a pulmonologist as the first step. Not sure if the two is related or not at this point.