How do you know if you have sarcoidosis?

Everyone different. Sarcoid can have many different manifestations. Characteristically you can have some of the follwoing: swollen lymph nodes, rashes, lung spots, eye changes, liver changes, skin rashes, etc. Each person is different and the diagnosis is made depending where the granulomas (the sarcoid biopsy inflammatory change) are found and if there is no other cause found. Your doctor can guide you here.
Many ways. Sarcoidosis can be diagnosed by abnormal chest x-ray, abnormal blood test called angiotensin converting enzyme level and finally by tissue biopsy, .