Welcome to Just Answer and thanks for your question. Generally there are no signs or symptoms that someone would notice until the latter stages of kidney failure. Then a person may notice fatigue, weakness, shortness of breath, etc.
Electrolyte imbalance may cause cardiac arrhythmias that lead to other symptoms (dizziness, fainting, palpitations, coma). Increasing blood urea levels can lead to encephalopathy (symptoms mimic dementia), or inflammation of the covering of the heart (pericarditis). Low levels of erythropoietin can result in anemia. There may also be congestive heart failure.
A simple blood test will detect the very beginning of kidney failure long before anyone has any symptoms or signs.
The tests are within a group of tests called a comprehensive metabolic panel, which includes tests for glucose, plus kidney and liver tests.