 When an abnormality is detected on a 24-hour urine collection the assumption is that this is due to a global metabolic defect present in both kidneys. However, this may not be the case. It is possible there could be a relative imbalance with both kidneys having a defect, but to different degrees or different defects in one or multiple electrolytes. It is also possible that one kidney has a dominant defect, but the contralateral kidney is normal, and therefore the 24-hour urine collection would only represent the dominant kidney with the defect. Finally, it is possible that the converse is true. One kidney has no defect, but the contralateral kidney has a minor defect. In this example, the 24-hour urine collection would appear normal as the dominant normal kidney masks the minor defect. This concept of differential kidney electrolyte handling was previously described in children. Therefore, understanding individual kidney metabolic profiles is important. 