Homogentisic Acid Alkaptonuria

Homogentisic Acid – Alkaptonuria

What it is

The Homogentisic Acid test measures the level of homogentisic acid in urine. Elevated levels are a hallmark of alkaptonuria, a rare inherited metabolic disorder caused by deficiency of the enzyme homogentisate 1,2-dioxygenase. This enzyme is required for the breakdown of tyrosine and phenylalanine. Without it, homogentisic acid builds up in the body, leading to dark-colored urine, connective tissue pigmentation (ochronosis), and long-term complications such as arthritis and heart disease.

Uses

This test is used to:

• Diagnose alkaptonuria by detecting excessive homogentisic acid in urine.
• Differentiate alkaptonuria from other metabolic or pigment disorders.
• Monitor disease progression and related complications.
• Support genetic counseling for families with inherited metabolic disorders.

Symptoms / Conditions That May Lead to the Test

Doctors may recommend this test if you have:

• Urine that turns dark brown or black upon standing.
• Early-onset joint pain or arthritis, especially in the spine or large joints.
• Abnormal skin, ear, or eye pigmentation (bluish-black discoloration).
• Family history of alkaptonuria or other metabolic disorders.
• Cardiac problems (e.g., valve calcification) or kidney/bladder stones linked to ochronosis.

Abnormal Results

• High Homogentisic Acid in Urine: Confirms alkaptonuria, especially in symptomatic patients.
• Normal Levels: Rule out alkaptonuria but do not exclude other metabolic or connective tissue disorders.

Results are often supported with genetic testing and clinical findings for a confirmed diagnosis.

Risks

This test usually requires a urine sample and carries minimal to no risks, including:

• No pain or discomfort beyond routine urine collection.
• Rare possibility of contamination affecting accuracy.