10947X CYSTINE, QUAN 24HR URINE

Test Code

CYSTIUR

Preferred Specimen

1.8 mL of a 24-hour urine collected in a 24-hour urine container

Minimum Volume

0.6 mL

Instructions

Do not use preservatives. Urine with a pH less than 2.0 will be rejected. Keep collection container refrigerated during 24-hour collection. Start collection after first morning void. Collect through first morning void of the next day. Take collection to the laboratory ASAP on the second day. The laboratory will mix sample well, measure total volume and remove an aliquot to send for testing. Freeze aliquot immediately.

Transport Temperature

Frozen

Specimen Stability

Room temperature: Unacceptable
Refrigerated: 48 hours
Frozen: 60 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

pH <2.0 • IVP within 48 hours of collection

Methodology
Chromatography/Mass Spectrometry

FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by the U.S. Food and Drug Administration. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

Setup Schedule

Set up: Tues, Thurs; Report available: 3-9 days

Clinical Significance

This quantitative test may be useful in the diagnosis and monitoring of cystinuria [1,2]. For diagnostic evaluation, this test may be ordered for individuals with clinical suspicion of cystinuria, including those who have symptoms of kidney stones or cystine crystals detected in urinalysis [2]. This test can also help monitor the effectiveness of treatment for individuals with cystinuria [2].

Cystinuria, an autosomal recessive genetic disorder that can cause kidney stones, is characterized by excessive excretion of cystine and dibasic amino acids in the urine. Around 1% to 2% of all kidney stones, and 6% to 8% of kidney stones in children, are caused by cystinuria [1]. Approximately 83% of patients with cystinuria who develop a kidney stone will have a recurrence within 5 years [2]. Common complications of cystinuria include chronic kidney disease and hypertension [2].

This test does not differentiate between free and bound cystine in patients taking cystine-binding thiol drugs [1]. This test alone is not sufficient to predict risk of kidney stones in individuals with cystinuria [1,2]. For young children when 24-hour urine collection is not possible, measurement of cystine concentration per gram of creatinine in the first-morning urine may be helpful as part of the diagnostic evaluation [1].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Leslie SW, et al. Cystinuria. In: StatPearls [Internet]. StatPearls Publishing; 2022. Accessed June 16, 2022. https://www.ncbi.nlm.nih.gov/books/NBK470527/
2. Daga S, et al. Urology. 2021;149:70-75.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.