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A dark-brown color was obtained by adding sodium hydroxide to the normal-colored urine sample (Figure 5). Urinary homogentisic acid (HGA) was identified by high-pressure liquid chromatography (4-mmol/mm creatinine). Plasma and synovial fluid HGA levels were normal. High urine HGA levels were also detected in samples from the patient's parents and several of his first-degree relatives. The patient underwent surgical removal of kidney stones that were black, porous, and soft in consistency.
A 46-Year-Old Man With a 4-Year History of Diffuse Brownish Black Pigmentation. Arch Dermatol. 1998;134(1):97–102. doi: