Aminoaciduria occurs when the urine contains abnormally high amounts of amino acids.

[2] In the healthy kidney, the glomeruli filter all amino acids out of the blood, and the renal tubules then reabsorb over 95% of the filtered amino acids back into the blood.

[3] In overflow aminoaciduria, abnormally high concentrations of amino acids in the blood plasma overwhelm the resorptive capacity of the renal tubules, resulting in high concentrations of amino acids in the urine.

[4] This may be caused by congenital disorders of amino acid metabolism,[3] for example, phenylketonuria,[5] or may be secondary to liver disease.

[3] In renal aminoaciduria, the renal tubules are unable to reabsorb the filtered amino acids back into the blood, causing high concentrations of amino acids in the urine.