A symptom is something the patient feels and reports, while a sign is something other people, including a doctor or a nurse may detect. For example, pain may be a symptom while a rash may be a sign.
Chronic kidney failure, as opposed to acute kidney failure, is a slow and gradually progressive disease. Even if one kidney stops functioning, the other can carry out normal functions. It is not usually until the disease is fairly well advanced and the condition has become severe that signs and symptoms are noticeable; by which time most of the damage is irreversible.
It is important that people who are at high risk of developing kidney disease have their kidney functions regularly checked. Early detection can significantly help prevent serious kidney damage.