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PTD - 219

Test Directory - Cystine (Quantitative, Urine)

Synonyms

Urinary cystine; quantitative cystinuriria

Clinical Indications

Cystinuria is an autosomal recessive defect in reabsorptive transport of cystine and the dibasic amino acids ornithine, arginine, and lysine from the luminal fluid of the renal proximal tubule and small intestine. The only phenotypic manifestation of cystinuria is cystine urolithiasis, which often recurs throughout a patient's lifetime.

Test Includes

Cystine, ornithine, arginine and lysine plus pH if EMU sample.

Request Form

Combined Pathology Blood form (Yellow/Black)

Availability

Analysed by Clinical Biochemistry, UCL Hospital, London if specific criteria met.

Specific Criteria

Confirmation of a positive cystine screening test or monitoring patients known to have cystinuria.

Turnaround Time

Same day

Specimen

Spot EMU urine or 24hr urine collection if formal documentation of urine volume is required.

Volume

5 ml

Container

White top universal or 24hr urine container (plain)

Causes for Rejection

Unlabelled sample. Not meeting specific criteria.

Reference Ranges

Cystine:creatinine ratio: 3 - 12 mmol/mol creat.
Ornitine:creatinine ratio: 0.5 - 2.0 mmol/mol creat.
Lysine:creatinine ratio: 6 - 41 mmol/mol creat.
Arginine:creatinine ratio: 0 - 3.7 mmol/mol creat.

Interpretation

Targets for monitoring patients with cystinuria:

  • Urine pH greater than 7.5

  • 24hr volume greater than 3 litres

  • Cystine concentration less than 1.0 mmol/L (EMU)

Lab. Handling

Processing: Test code UCYSQ. If 24hr urine collection mix thoroughly before taking two aliquots. If EMU (spot urine) sample, measure pH immediately and record this.
Referral: Store at 4C in separating fridge (CB39) until dispatch.


Version 1.0 / April 2014                                                                                                          Approved by: Consultant Biochemist