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Epic Code LAB848 Cystinuria Profile, Quantitative, Random, Urine

Important Note

Order as Reference Miscellaneous #LAB848; indicate complete test name when ordering.

Additional Codes

Mayo Code: CYSR

Epic: LAB848

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Biochemical diagnosis of cystinuria using random urine specimens

Specimen Type

Urine


Necessary Information


1. Patient's age is required.

2. Include family history, clinical condition (asymptomatic or acute episode), diet, and drug therapy information



Specimen Required


Supplies: Urine Tubes, 10 mL (T068)

Specimen Volume: 2 mL

Collection Instructions: Collect a random urine specimen.


Specimen Minimum Volume

1 mL

Specimen Stability Information

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

Reject Due To

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

Day(s) Performed

Monday through Friday

Reference Values

Amino Acid

Age groups

<2 months

2-35 months

3-6 years

7-17 years

≥18 years

Arginine

Arg

<250

<147

<81

<42

<65

Ornithine

Orn

<344

<238

<228

<291

<193

Cystine

Cys

<486

<285

<111

<84

<142

Lysine

Lys

<2217

<1321

<814

<463

<295

 

All results reported as nmol/mg creatinine.

Clinical 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 and the presence of blood in the urine (hematuria). 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 the short arm of chromosome 2 and SLC7A9 on the long arm of chromosome 19. Initially, the disease was classified into subtypes I, II, and III (type II and III are also referred as non-type 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.

Cautions

No significant cautionary statements

Interpretation

Individuals who are homozygous or compound heterozygous for 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 non-type 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.

Reporting Name

Cystinuria Profile, QN, Random

Method Name

Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Method Description

Quantitative analysis of amino acids is performed by liquid chromatography tandem mass spectrometry. Patient samples are combined with isotopically labeled internal standard. Following protein precipitation, the supernatant is subjected to hydrophilic-interaction liquid chromatography for the separation of isomers with MS/MS detection of the underivatized amino acids.(Unpublished Mayo method)

CPT Code Information

82136

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CYSR Cystinuria Profile, QN, Random 90784-0

 

Result ID Test Result Name Result LOINC Value
23517 Arginine 30062-4
23516 Ornithine 30049-1
23514 Cystine 30065-7
23515 Lysine 30048-3
50416 Reviewed By 18771-6

Report Available

3 to 5 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

Clinical Reference

1. Servais A, Thomas K, Strologo LD, et al. Cystinuria: clinical practice recommendation. Kidney Int. 2021;99(1):48-58

2. Palacin M, Goodyer P, Nunes V, Gasparini P: Cystinuria. In: Valle DL, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw Hill; 2019. Accessed October 24, 2024. Available at https://ommbid.mhmedical.com/content.aspx?bookid=2709&sectionid=225555540