Cystine, Quant, 24 Hour Urine (CYSQN)

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Test Code: CYSTSO

Overview
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Specimen
Performing
Clinical/Interpretive
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Coding

Synonyms/Keywords

Amino Acid, Cystine, Quantitative, Urine, Cystinuria

Cystine, Qnt, 24H Ur (CYSQN)

Cystinuria Profile, Quantitative, 24 Hour, Urine

24 CYSTSO

Useful For

Diagnosis of cystinuria

Specimen Requirements

Specimen Type	Preferred Container/Tube	Acceptable Container/Tube	Specimen Volume	Specimen Minimum Volume (allows for 1 repeat)	Pediatric Minimum Volume (no repeat)
24-Hour Urine	Plastic, 10 mL urine tube		5 mL	1 mL

Collection Processing Instructions

1. Collect before intravenous pyelogram.

2. Collect urine for 24 hours.

3. Add 20 mL of toluene as preservative at start of collection. If toluene is not available, refrigerate during collection.

4. Mix well before taking 5-mL aliquot.

Additional Information:

1. 24-Hour volume is required.

2. See Mayo Labs website for additional information regarding acceptable preservatives and collection details. 

Specimen Stability Information

Specimen Type	Temperature	Time
Urine	Frozen (preferred)	70 days
Urine	Refrigerated	14 days

Rejection Criteria

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Performing Laboratory Information

Performing Location	Day(s) Test Performed	Report Available	Methodology/Instrumentation
Mayo Clinic Laboratories	Monday through Friday	3 to 5 days	Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reference Lab

Mayo Clinic Laboratories

Test Information

Cystinuria is an inborn error of metabolism resulting from poor absorption and reabsorption of the amino acid cystine in the intestines and kidneys. This leads to an accumulation of poorly soluble cystine in the urine and results in the production of kidney stones (urolithiasis). Symptoms may include acute episodes of abdominal or lower back pain, presence of blood in the urine (hematuria), and recurrent episodes of kidney stones may result in frequent urinary tract infections, which may ultimately result in renal insufficiency. The combined incidence of cystinuria has been estimated to be 1 in 7000.

Cystinuria is an autosomal recessive disease, but some heterozygous carriers have an autosomal dominant, incomplete penetrance appearance with elevated, but typically nondisease causing, urinary cystine excretion. Cystinuria is caused by variants in genes, SLC3A1 on chromosome 2p and SLC7A9 on chromosome 19q. Initially, the disease was classified into subtypes I, II, and III (type II and III are also referred as nontype-I) based on the amount of urinary cystine excreted in heterozygous parental specimens. A new classification system has been proposed to distinguish the various forms of cystinuria: type A, due to variants in the SLC3A1 gene; type B, due to variants in the SLC7A9 gene; and type AB, due to 1 variant in each SLC3A1 and SLC7A9 gene.

Reference Range Information

CYSTINE

3-15 years: < or = 53 mcmol/24 hours

> or = 16 years: < or = 115 mcmol/24 hours

LYSINE

3-15 years: < or = 140 mcmol/24 hours

> or = 16 years: < or = 290 mcmol/24 hours

ORNITHINE

3-15 years: < or =16 mcmol/24 hours

> or = 16 years: < or = 70 mcmol/24 hours

ARGININE

3-15 years: < or = 25 mcmol/24 hours

> or = 16 years: < or = 64 mcmol/24 hours

Conversion Formulas:

Result in mcmol/24 hours x 0.24=result in mg/24 hours

Result in mg/24 hours x 4.17=result in mcmol/24 hours

Interpretation

Homozygotes or compound heterozygotes with cystinuria excrete large amounts of cystine in urine, but the amount varies markedly. Urinary excretion of other dibasic amino acids (arginine, lysine, and ornithine) is also typically elevated. Plasma concentrations are generally normal or slightly decreased.

Individuals who are homozygous and heterozygous for nontype I cystinuria can be distinguished by the pattern of urinary amino acids excretion: homozygous individuals secrete large amounts of cystine and all 3 dibasic amino acids, whereas heterozygous individuals secrete more lysine and cystine than arginine and ornithine.

Outreach CPTs

CPT	Modifier (if needed)	Quantity	Description	Comments
82136