Urine Cystine (creatinine ratio)

This test measures the amount of cystine in your urine and reports it relative to creatinine to account for how concentrated or dilute the sample is. Cystine is a compound formed from two cysteine molecules and is normally present in small amounts in urine.

The measurement helps evaluate how your kidneys handle certain amino acids. It is especially useful for detecting and monitoring cystinuria, an inherited condition where excess cystine in urine can form crystals and stones.

Too much cystine in urine can lead to cystine kidney stones, which may recur and cause pain, blockage, or infections. Your clinician may order this test if you have a history of kidney stones, hexagonal crystals seen on urine microscopy, a family history of cystinuria, or symptoms suggestive of stones.

Results can guide prevention and treatment plans, including hydration targets, urine alkalinization, dietary changes, and medications that bind cystine. In children and young adults, early identification helps reduce the long-term risk of stone complications and kidney damage.

Your result is interpreted with your age, how the sample was collected, and other lab findings. Children often have higher values than adults, and a single random sample can be influenced by recent diet or how concentrated your urine is. If your level seems unexpectedly high, your clinician may suggest repeating the test or performing a 24-hour urine collection for confirmation.

If results point to cystinuria, additional evaluation may include a urine amino acid profile, genetic testing, stone analysis, and review of your urine pH. When elevated levels persist, your care plan may include increasing fluid intake, lowering dietary sodium, adjusting urine pH, and considering medications that make cystine more soluble. Seek medical care promptly if you develop severe flank pain, visible blood in urine, fever, or difficulty passing urine.