Clinical Information

Cystine, 24-Hour Urine -

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.