After a year of testing, I was diagnosed with Sarcoidosis in December. In my case, I went for a chest x-ray after several weeks of chest pressure and a slight cough. The x-ray showed a small nodule and a subsequent CT scan showed multiple nodules throughout both lungs and an enlarged lymph node.
I found out that there isn't a test (other than a biopsy) that can determine Sarc 100%. It is a case of ruling out other causes of the nodules. I had numerous blood, urine and lung function tests - all of which were good. I had a skin test to rule out TB. I know that an ACE blood test can (but not always) show signs of Sarc. So can your calcium levels. But nothing is conclusive. I had a 2 bronchoscopies done as well, one of which was normal and one inconclusive.
Apparently, the small (>1cm) nodules are hard to get a biopsy on, so they usually monitor them for a couple of years to see if they grow. This seems to be the norm, but it sure can be a long period! Again, in my case, I was ultimately sent to a chest surgeon who did a mediastinoscopy on me and biopsied 3 chest lymph nodes, all of which tested positive for Sarcoidosis.
I hope this helps. The lungs are generally affected but other organs can be as well. Some people have skin symptoms, eye symptoms and joint problems. In my case, it seems it just my lungs (touch wood) and, since I have no symptoms now, I don't need treatment, just monitoring.
Take care. Murphy