Copper, Urine

The Copper, Urine test (urinary copper; Cu, urine) is used to assess disorders of copper metabolism, including the diagnosis and longitudinal monitoring of Wilson disease. It helps follow response to treatment such as chelation or other anti-copper therapy. This measurement also assists in evaluating increased copper exposure or toxicity and in identifying deficiency states or excessive urinary loss. Clinical interpretation is improved by pairing results with ceruloplasmin and serum copper and by reviewing 24-hour urinary copper excretion and the urine copper/creatinine ratio.

Copper functions as a cofactor for numerous enzymes involved in iron metabolism, connective tissue cross-linking, cellular energy generation, melanin production, and neurologic processes. Dietary copper is absorbed in the small intestine and delivered to the liver, after which most circulating copper is bound to ceruloplasmin. Biliary excretion is the main route of elimination; only a small fraction is normally lost in urine. Urinary copper excretion is typically increased in Wilson disease and can also be elevated in chronic active hepatitis and Indian childhood cirrhosis. Accordingly, results are best interpreted with complementary data, including ceruloplasmin and serum copper concentrations. Copper deficiency arises in settings of severe malabsorption (eg, cystic fibrosis, celiac disease) and may present with neutropenia, osteoporosis, and microcytic anemia; the X-linked Menkes disorder causes profound deficiency in infancy. The urine copper/creatinine ratio and 24-hour urinary copper output help distinguish physiologic variability from pathologic elevations.