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Test ID: CYSQN    
Cystinuria Profile, Quantitative, 24 Hour, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of cystinuria

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

Biochemical diagnosis of cystinuria. Measures cystine, lysine, ornithine, and arginine.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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 Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

CYSTINE

3-15 years: 11-53 mcmol/24 hours

> or =16 years: 28-115 mcmol/24 hours

 

LYSINE

3-15 years: 19-140 mcmol/24 hours

> or =16 years: 32-290 mcmol/24 hours

 

ORNITHINE

3-15 years: 3-16 mcmol/24 hours

> or =16 years: 5-70 mcmol/24 hours

 

ARGININE

3-15 years: 10-25 mcmol/24 hours

> or =16 years: 13-64 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 Provides information to assist in interpretation of the test results

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.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Saravakos P, Kokkinou V, Giannatos E: Cystinuria. Current Diagnosis and Management. Urology April 2014;4(83):693-699

2. Palacin, M, Goodyer, P, Nunes V, Gasparini P: Cystinuria. Edited by D Valle, AL Beaudet, B Vogelstein, et al. New York, McGraw-Hill, 2014. Accessed 6 July 2016. Available at http://ommbid.mhmedical.com/content.aspx?sectionid=62653976&bookid=971&Resultclick=2

Special Instructions Library of PDFs including pertinent information and forms related to the test