Urine may appear dark brown or black if certain compounds are present. Sometimes the darkening occurs only after the urine has stood for several hours under conditions favoring oxidation (sunlight, air).
Darken on Standing (Oxidation)
Comments
melanogenuria (melanuria)
metastatic melanoma or Addison's disease, hemochromatosis (see previous section)
methemoglobin
converted from hemoglobin, especially if urine acid
