Melanogen compounds may be excreted in the urine. The urine turns brown then black if it is allowed to stand in the air and sunlight, which results in oxidation of the melanogen compounds to melanin.



(1) metastatic malignant melanoma

(2) primary adrenal insufficiency (Addison's disease, secondary to ACTH stimulation of melanocortin-2 receptor according to Stewart)

(3) hemochromatosis


Many affected patients show melanosis (diffuse skin coloration).


Melanin pigment may be seen in renal tubular epithelial cells in the urine sediment.


Screening tests are nonspecific:

(1) ferric chloride test (dark blue; may also be positive with salicylates)

(2) Ehrlich's aldehyde reagent

(3) Thormahlen's test (sodium nitroprusside, potassium hydroxide, and acetic acid; positive reaction deep blue)


DOPA oxidase levels in urine may be increased.


Differential diagnosis:

(1) other urinary compounds that darken on standing in air and sunlight (see below)


To read more or access our algorithms and calculators, please log in or register.