Melanin

Melanin is a macromolecular compound synthesized by tyrosine via 3,4-dihydroxyphenylalanine (ie, dopa) and nevi. It is a brown to black pigment with a colorless melanin precursor. When congenital lack of tyrosinase in melanocytes, albinism can form. A tumor formed by melanocytes is called a melanoma. Normal urine contains no melanin, so the qualitative test is negative. Melanoma has a large amount of tyrosinase, so melanin can appear in the urine of patients with melanoma. The eyes are the most common sites of melanoma, and patients with liver metastatic melanoma often have a large amount of melanin in their urine, which can be used as an important basis for the diagnosis of the disease. In addition, melanin is occasionally present in the urine of patients with chronic malaria and adrenal insufficiency (Addison's disease).