Hyperammonemia may be a metabolic disturbance characterized by more than ammonia within the blood. It is a dangerous condition that will cause brain injury and death. It may be primary or secondary. Ammonia is a substance that contains nitrogen. It is a product of the catabolism of protein. It is converted to the less toxic substance urea before excretion in urine by the kidneys. The metabolic pathways that synthesize urea involve reactions that start in the mitochondria and then move into the cytosol. The process is understood because of the urea cycle, which comprises several enzymes acting in sequence. It is greatly exacerbated by common deficiency disease, which raises ammonia levels further.