In the beginning, kidney failure may be asymptomatic (not producing any symptoms). As kidney function decreases, the symptoms are related to the inability to regulate water and electrolyte balances, to clear waste products from the body, and to promote red blood cell production. Lethargy, weakness, shortness of breath, and generalized swelling may occur. Unrecognized or untreated, life-threatening circumstances can develop.
Metabolic acidosis, or increased acidity of the body due to the inability to manufacture bicarbonate, will alter enzyme and oxygen metabolism, causing organ failure.
Inability to excrete potassium and rising potassium levels in the serum (hyperkalemia) is associated with fatal heart rhythm disturbances (arrhythmias) including ventricular tachycardia and ventricular fibrillation.
Rising urea levels in the blood (uremia) can affect the function of a variety of organs ranging from the brain (encephalopathy) with alteration of thinking, to inflammation of the heart lining (pericarditis), to decreased muscle function because of low calcium levels (hypocalcemia).
Generalized weakness may be due to anemia, a decreased red blood cell count, because lower levels of erythropoietin produced by failing kidneys do not adequately stimulate the bone marrow. A decrease in red cells equals a decrease in oxygen-carrying capacity of the blood, resulting in decreased oxygen delivery to cells for them to do work; therefore, the body tires quickly. As well, with less oxygen, cells more readily use anaerobic metabolism (an=without + aerobic=oxygen) leading to increased amounts of acid production that cannot be addressed by the already failing kidneys.
As waste products build in the blood, loss of appetite, lethargy, and fatigue become apparent. This will progress to the point where mental function will decrease and coma may occur.
Because the kidneys cannot address the rising acid load in the body, breathing becomes more rapid as the lungs try to buffer the acidity by blowing off carbon dioxide. Blood pressure may rise because of the excess fluid, and this fluid can be deposited in the lungs, causing congestive heart failure.