Alkaptonuria (Black Urine Disease) Workup

Updated: Mar 18, 2021
  • Author: Karl S Roth, MD; Chief Editor: Maria Descartes, MD  more...
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Workup

Laboratory Studies

In patients with alkaptonuria, homogentisic acid can be identified in urine using gas chromatography – mass spectroscopy. Spectrophotometric quantitation shows 2 orders of magnitude elevations above normal.

Because many patients present without dark urine, looking for homogentisate in all patients with radiographic evidence of osteoarthritis may be advisable.

After DNA extraction from whole blood, screening for mutations can be performed with polymerase chain reaction (PCR) technique.

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Imaging Studies

Spinal radiography reveals disk degeneration combined with dense calcification, particularly in the lumbar area.

Chest radiography is advised to assess for possible involvement of aortic or mitral valves.

In affected individuals older than 55 years, CT scanning may provide evidence of coronary artery calcifications.

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Other Tests

Electrocardiography may be advisable, with particular attention directed at any signs of myocardial insufficiency.

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Procedures

Other studies and procedures should be directed at the joint disease itself.

Joint replacements may become necessary in severely affected larger joints.

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Histologic Findings

In association with the gross visual finding of black-stained cartilage in various areas of the body (eg, larynx, costochondral junctions, trachea), microscopic examination reveals pigment deposition within and outside cells in these tissues.

No specific stain is available to distinguish homogentisate-derived pigment from melanin, and the 2 compounds have similar solubility characteristics.

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