Cystinuria is a condition characterized by the buildup of cystine crystals or stones in the kidneys and bladder.
Cystine is an amino acid, one of the building blocks of proteins. As the kidneys filter blood to create urine, cystine is normally absorbed back into the bloodstream. People with cystinuria cannot properly reabsorb cystine into their bloodstream and the amino acid accumulates in their urine.
As urine becomes more concentrated in the kidneys, the excess cystine forms crystals. As these crystals become larger, they form stones that may lodge in the kidneys or in the bladder. Sometimes cystine crystals combine with calcium molecules in the kidneys to form larger stones. These crystals and stones can create blockages in the urinary tract and reduce the ability of the kidneys to eliminate waste through urine. The stones also provide sites where bacteria may cause infections.
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