In a patient with alkaptonuria, urine testing will typically reveal high levels of homogentisic acid. This is an intermediate product of the metabolism of tyrosine and phenylalanine and is the metabolic waste product created when the body breaks down these amino acids. It is produced in higher than normal levels in alkaptonuria, due to a deficiency of the enzyme homogentisate 1,2-dioxygenase. This enzyme is responsible for breaking down homogentisic acid and thus its deficiency leads to its accumulation in the body.
Urine tests for homogentisic acid are used to diagnose alkaptonuria in patients, as well as to monitor disease progression and therapeutic efficacy. The presence of high levels of homogentisic acid in the urine can also be indicative of other diseases such as tyrosinemia, a defect in the enzyme involved in the metabolism of tyrosine. Additionally, the presence of high levels of homogentisic acid in the urine can also be indicative of a more serious underlying condition such as tumor lysis syndrome or multiple myeloma.
In addition to homogentisic acid, urine testing in patients with alkaptonuria can also reveal the presence of other metabolites, such as ochronotic pigment, which is a dark-colored pigment produced when homogentisic acid combines with proteins in the body. This pigment is typically found in the urine and can be an indication of the presence of the disease.