Cystine (Quantitative), Urine

Cystine (Quantitative), Urine

Test Name: Cystine (Quantitative), Urine

Specimen: Urine
Method: Quantitative chromatographic / mass spectrometric analysis, depending on laboratory methodology.

Clinical Significance

Cystine is an amino acid formed from cysteine and is normally present in urine in small amounts. Elevated urinary cystine is primarily associated with cystinuria, an inherited disorder causing impaired renal reabsorption of cystine and certain other amino acids. Cystine can crystallize in the urinary tract and contribute to recurrent kidney stone formation.

Why is this test done?

• Evaluation of suspected cystinuria
• Investigation of recurrent or early-onset kidney stones
• Assessment of unexplained urinary cystine elevation
• Monitoring patients with known cystinuria during treatment

Interpretation

• Normal: Low or expected urinary cystine excretion.
• Elevated: May support cystinuria, particularly when accompanied by increased urinary excretion of other dibasic amino acids.

Note: Results should be interpreted along with clinical findings, urine amino acid profile, kidney stone history, and other relevant investigations. Reference ranges may vary according to age, urine collection type, and laboratory method.