Darkening of urine on standing is associated with
Alkaptonuria is caused by defect of the enzyme homogentisate 1,2-dioxygenase(homogentisic acid oxidase).The disorder comes to attention due to change in colour of urine to brownish black/ staining of diapers.The urine becomes dark on standing,especially if the pH of urine is alkaline,due to the presence of homogentisic acid.Excessive urine homogentisate results in positive reducing substances. Reference:Essential pediatrics-Ghai,8th edition,page no:653.
Alkaptonuria
Cystinuria
Fabry's disease
Tyrosinemia
Metabolic disorders