Dark black urine, also known as dark brown urine, is most often seen in patients with melanoma. Melanoma produces too much melanin. In the liver small melanin is reduced to melanogen. If a large amount of melaninogen is excreted from the urine, it becomes melanin after oxidation wren times, so the urine of a melanoma patient, if left for a little while, becomes black urine. The examination of urine dark black: 1.The addition of appropriate amount of alkaline reagent in urine can accelerate the appearance of urine black change; 2.The addition of Ban’s reagent after alkalinization of urine shows brown color, and the general reducing substance shows orange-yellow color. 3, adding high iron chloride reagent can make the urine appear purple-black. 4, taking 0.5ml of urine and adding 5ml of saturated silver nitrate aqueous solution can immediately show black, but vitamin C can cause false positive results. The above screening method and then by chromatography, spectrophotometric determination, or urinary black acid oxidase activity determination, you can confirm the diagnosis. Blood tests: The renal threshold for urinary black acid is very low, and large amounts of urinary black acid are excreted in the urine, up to several grams per day, often without a significant increase in blood concentration. Differentiation: Bilirubin, porphyrins, myoglobin and hemoglobin can all darken the urine and should be differentiated.