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Company
Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
This test measures the amount of cystine, an amino acid that can form hard crystals, in your urine compared with creatinine, a marker that helps correct for how concentrated your urine is. Reporting cystine relative to creatinine makes the result easier to compare from one sample to another, even if you drank more or less fluid.
It is performed on a full day urine collection, which pools all urine you pass over a day to capture typical excretion. The result helps your care team see how much cystine your kidneys are releasing and whether this pattern is consistent with cystinuria or with a tendency to form cystine kidney stones.
This test is used to evaluate for cystinuria, a genetic condition that causes high cystine levels in urine and can lead to recurring kidney stones, urinary blockage, and infections. It is also used to monitor how well treatments such as increased hydration, urine alkalinization, and thiol medications are lowering urinary cystine.
Your clinician may order it after a cystine stone is identified, when you have strong family history or symptoms that suggest cystinuria, or to track control over time. Understanding your cystine excretion helps tailor prevention strategies and reduce the chance of future stone events and complications.
Lower ratios typically mean less cystine relative to creatinine, which generally suggests a lower risk for forming cystine stones. Higher ratios indicate more cystine in the urine and a higher likelihood of crystal formation, especially if urine is very concentrated or acidic.
If your result is above your target for management, your clinician may adjust prevention steps such as fluid goals, dietary protein guidance, alkalinizing therapy, or cystine-binding medications. If the result is unexpectedly low or high, the team may confirm that the collection was complete, repeat testing, or consider additional tests, for example stone analysis or genetic testing, to clarify the cause. Always discuss your individual goals and next steps with your clinician.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Missing even one void during a full day collection can falsely lower the result. Carefully follow instructions, record start and end times, and return the entire volume.
Cystine can precipitate in warm or standing urine. Keeping the container cool and delivering it promptly helps preserve accuracy and prevents losses.
Low fluid intake concentrates urine and can raise the measured ratio, while high intake dilutes urine and can lower it. Aim for steady, consistent hydration before and during collection.
More acidic urine favors cystine crystallization. Alkalinizing therapy and diet can change acidity and may lower the risk of crystal formation and influence results.
High intake of animal protein and salt can increase urinary cystine. Following personalized nutrition guidance supports better control of excretion.
Tiopronin, penicillamine, and captopril can bind cystine and lower free cystine in urine. Alkalinizing salts and some supplements may also affect results; tell your clinician what you take.
Creatinine is used to normalize results and depends on kidney function and muscle mass. Significant changes in either can shift the ratio without reflecting a true change in cystine production.
References