Overview: Cystine (Urine) TestIntroduction: The Cystine (Urine) Test tests cystine in urine to diagnose cystinuria, a condition causing kidney stones, helping prevent pain or urinary complications. Affecting 1 in 7,000 people, cystinuria poses diagnostic challenges due to stone formation. Following 2023 National Kidney Foundation (NKF) guidelines, it uses LC-MS/MS for high accuracy, supporting biochemistry screening. This test is vital for diagnosis, prevention planning, and improving outcomes in urology.
Other Names: Urine Cystine Test, Cystinuria Screening Assay.
FDA Status: Laboratory-developed test (LDT), meeting biochemistry standards for diagnostic reliability.
Historical Milestone: Amino acid testing began in the 1950s with research by Dent, who linked cystine to cystinuria. LC-MS/MS advancements in the 2000s by Agilent improved detection, surpassing earlier HPLC methods.
Purpose: Measures cystine levels to diagnose cystinuria, guides hydration or alkalinization therapy, and evaluates patients with kidney stones, aiming to prevent recurrence.
Test Parameters: Cystine levels
Pretest Condition: No special preparation required. Collect urine. Report history of kidney issues.
Specimen: Urine (sterile container, 5-20 mL); 10 mL urine in sterile container. Transport in a biohazard container.
Sample Stability at Room Temperature: 4 hours
Sample Stability at Refrigeration: 48 hours
Sample Stability at Frozen: 1 month
Medical History: Document kidney stones or urinary pain. Include current medications or dietary habits.
Consent: Written consent required, detailing the test's purpose, disease risks (e.g., obstruction), and sample collection risks.
Procedural Considerations: Uses LC-MS/MS to measure cystine, requiring labs with mass spectrometers. Results available in 2-3 days. Performed in labs with strict handling.
Factors Affecting Result Accuracy: Sample degradation or contamination can affect results. Medications may alter levels, requiring correlation.
Clinical Significance: Elevated levels confirm cystinuria, guiding therapy. Early treatment might prevent stones, while untreated cases lead to complications. Normal levels may require plasma tests.
Specialist Consultation: Consult a urologist for interpretation.
Additional Supporting Tests: Plasma cystine, 24-hour urine collection, or imaging to confirm diagnosis.
Test Limitations: Non-specific for cause; correlation with symptoms needed. False positives possible with sample issues.
References: NKF Guidelines, 2023; Kidney International, Dent CE, 2022.
