Diagnosis of Alkaptonuria
Diagnosis of Alkaptonuria can be challenging, especially because early symptoms are mild or nonspecific. However, a darkening of the urine — often noted in infancy or childhood — is usually the first sign. If left undiagnosed, symptoms progress and become more noticeable in adulthood.
Clinical Signs
Doctors may suspect alkaptonuria if a patient presents with:
- Urine that turns dark brown or black after standing
- Bluish-black pigmentation in the sclera (eye whites) or ear cartilage
- Early-onset osteoarthritis or chronic joint pain, especially in the spine or knees
- Stiffness in the lower back or hips from a young age
- Pigmented spots in sweat glands or on skin folds
Urine Testing
A simple urine test can detect elevated levels of homogentisic acid. When urine is exposed to air, HGA oxidises and turns dark — a tell-tale sign.
A more precise test involves gas chromatography–mass spectrometry (GC-MS), which accurately measures HGA levels in urine.
Genetic Testing
Confirmation of the diagnosis can be done through DNA testing, identifying mutations in the HGD gene. This may also assist in identifying carriers within a family and guide future family planning.
Imaging and Joint Assessment
For adults of all ages with joint pain across the body, imaging such as X-rays or MRI scans may reveal signs of spinal degeneration or cartilage damage. While these are not specific to alkaptonuria, they support the diagnosis when combined with urine tests.
In South Africa, testing may be limited in some state facilities, but specialist referral is possible through major academic hospitals and genetics clinics.
Early diagnosis allows for monitoring and intervention before irreversible joint damage sets in.
Related Topics
Alkaptonuria testing, Urine test for alkaptonuria, Genetic testing, HGA levels, Metabolic disorder diagnosis, Black urine diagnosis, Rare disease screening, Early detection, Alkaptonuria symptoms, Ochronosis diagnosis, Enzyme deficiency test, Genetic disorder identification
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