Bacterial degradation of unabsorbed tryptophan in the intestine leads to excessive indole production and thus to indicanuria which, on oxidation to indigo blue, causes a peculiar bluish discoloration of the diaper (indoluria).

[5] Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is "turned off".

[3] Parents can undergo genetic testing to see if their child will get this syndrome, but most do not find out until they see the symptoms mentioned below.

[citation needed] Blue diaper syndrome affects males and females equally.

[3] This syndrome is diagnosed through clinical evaluation and a fresh urine sample [3] A diagnosis is usually made through clinical evaluation, observing detailed patient history then identifying the possible characteristic symptoms and testing fresh urine samples to enhance such evidence.

[citation needed] Genetic counseling can also be beneficial, as well as taking part in clinical trials.