Urinalysis and Body Fluids 6th Edition by Majorie DiLorenzo, Susan Strasinger

Exercise 9

A urine that turns black after sitting by the sink for several hours could be indicative of:

A. Alkaptonuria

B. MSUD

C. Melanuria

D. Both A and C

Step 1 of 2

Alkaptonuria:

• This is the third chief disorder in phenylalanine-tyrosine pathway

• Failure to inherit the homogentisic acid oxidase enzyme causes this disorder

• Without this enzyme, the phenylalanine-tyrosine pathway does not get completed as homogentisic acid collects in urine, blood, and tissues

• The name alkaptonuria is assigned from alkali lover, because urine becomes alkaline, and dark after standing for a prolonged time in room temperature

Melanuria:

• Melanuria is the presence of melanin pigment in urine

• Melanin is the pigment, which gives dark color to eyes, skin, and hair

• Deficiency of melanin leads to albinism

• Melanin in urine causes the urine to appear dark

• When exposed to air for long time, urine begins to appear dark

Therefore, urine that turns black when kept idle in sink for more hours is an indication of “alkaptonuria and melanuria”. Hence, the correct answer is option.