Cystine, Random Urine with Creatinine

Test Code

401

CPT Codes
82131, 82570

Includes

Creatinine

Preferred Specimen

1.8 mL random urine collected in a sterile screw-cap container

Minimum Volume

0.6 mL

Other Acceptable Specimens

Catheterized urine • First void clean catch urine • Random clean catch urine

Instructions

Do not use preservatives. Urine with a pH <2.0 will be rejected.
Do not thaw. Patient age is required for correct reference range.

Transport Container

Transport tube

Transport Temperature

Frozen

Specimen Stability

Room temperature: Frozen only
Refrigerated: Frozen only
Frozen: 28 days

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

Received room temperature • Received refrigerated • Received thawed • pH <2.0

Methodology
Liquid Chromatography/Mass Spectrometry (LC/MS)

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 FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

Reference Range

Cystine

Pediatric (<18 Years)			3.2-12.6 mmol/mol creat
Adult			3.4-16.4 mmol/mol creat

Creatinine, Random Urine

0-6 Months	0.18-2.48 mmol/L
7-11 Months	0.18-2.74 mmol/L
1-2 Years	0.18-9.72 mmol/L
3-8 Years	0.18-11.49 mmol/L
9-12 Years	0.18-14.14 mmol/L
>12 Years	1.77-23.31 mmol/L

Clinical Significance

This quantitative test may be useful for evaluation of individuals with clinically suspected cystinuria, including those with symptoms of kidney stones or cystine crystals detected in urinalysis [1]. Although 24-hour urine testing is generally preferred for diagnostic evaluation and monitoring of cystinuria [2], random or first-morning void urine collection may be helpful for diagnosis when 24-hour urine collection is not feasible (eg, for young children) [3].

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 [1]. Common complications of cystinuria include chronic kidney disease and hypertension [1].

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].

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

References
1. Daga S, et al. Urology. 2021;149:70-75.
2. Williams JC Jr, et al. Urolithiasis. 2021;49(1):1-16.
3. Servais A, et al. Kidney Int. 2021;99(1):48-58.

Performing Laboratory

Quest Diagnostics Nichols Institute-San Juan Capistrano, CA

33608 Ortega Highway

San Juan Capistrano, CA 92675-2042

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.