Study Visit 3 will occur at the OCTRI and will be devoted to the HCTZ test. During the course of the HCTZ test, subjects will have an plastic tube (an IV) placed in an arm vein, have vital signs checked and receive 50mg of HCTZ to take by mouth . Subjects will provide 8 urine samples and 3 blood samples. The time required for this visit is expected to be 6 hours.