Diffuse connective tissue disease involves multiple disciplines, so the correct diagnosis begins with history taking, a physical examination of the joints and spine, and general tests such as blood tests, urine tests, liver and kidney functions, which are all helpful in making a diagnosis. There are also specific tests, including arthroscopy, to look at the structure of the joints, to obtain joint fluid for testing, and serum autoantibody and complement level testing. Because diffuse connective tissue disease is the category of rheumatic diseases, but this disease includes many diseases, such as systemic lupus erythematosus, rheumatoid arthritis, primary dry syndrome, polymyositis, dermatomyositis, as well as ankylosing spondylitis, vasculitis and so on some diseases. But for each disease, the history, the tests, including specific tests, including laboratory tests, these results are different, for example, like in lupus erythematosus, the total complement will be reduced, or complement C3, complement C4 will also be reduced, and there are also antinuclear antibodies that behave differently. Therefore, if you suspect diffuse connective tissue disease, you have to see a doctor, and the doctor can make a clear diagnosis based on the history, and the results of various tests to make a comprehensive judgment.