If your doctor suspects that your joint symptoms are related to a bacterial infection, he or she probably will remove fluid from the affected joint with a needle and will have it analyzed in a lab. You may have blood and urine tests. If your doctor thinks a sexually transmitted disease may be causing the problem, he or she will do a pelvic examination if you are a woman and a swab of the penis and a urine test if you are a man. The urine and swabbed material are sent to be tested in a laboratory. Tests are not available to diagnose most viral diseases. However, some of the more common viral causes of arthritis, such as parvovirus, hepatitis B, hepatitis C and HIV, can usually be diagnosed with blood tests.