Primary hyperoxaluria type I (PH1) is an autosomal recessive disorder of glyoxylate metabolism resulting from a deficiency of the liver peroxisomal enzyme alanine-glyoxylate transaminase, encoded by the AGXT gene. This leads to calcium salts forming in the kidneys and other organs causing progressive decline in renal function and end stage renal disease (ESRD). The age of onset of symptoms ranges from childhood to adulthood but 80-90% of affected individuals present in late childhood or early adolescence. Presumptive diagnosis is made measuring urine oxalate:creatinine ratio and plasma oxalate concentration. Diagnostic confirmation can be made by AGT enzyme activity from liver biopsy, or by gene sequencing, which is less invasive. Carrier testing for biological family members is available once mutations are known.