Recurrent infections with certain kinds of bacteria or fungi are the first clue of CGD. To confirm the diagnosis, the doctor will usually request a blood test called the nitroblue tetrazolium dye reduction test (NBT). This test indicates how well the patient's phagocytes metabolize oxygen (as in the respiratory burst described previously). If the patient has CGD, the NBT will indicate an abnormal respiratory burst. Tests of phagocyte killing of bacteria may also be performed. Once the diagnosis is made, special X-rays, blood, and urine tests may be done to establish baseline conditions. Knowing the baseline condition can be very helpful in understanding future problems, should they occur.