Occurrence:
(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)
