What are other Names for this Test? (Equivalent Terms)
- Cystinuria Panel of Urine Tests
What is the Cystine Urine Test? (Background Information)
- Cystine is a compound formed by the fusion of two molecules of cysteine, a non-essential amino acid; meaning that the body can produce it in sufficient quantities. It may form crystals in the bladder, kidneys, or ureters, which may result in a disease
- Cystine crystals are associated with a disease called cystinuria. It is a genetic disorder whereby cystine is inadequately filtered by the kidneys. This causes cystine buildup in urine, which leads to cystine crystallization (forming a type of kidney stone)
- The genes that give instructions for the proteins associated with cystine absorption by the kidneys are called SLC3A1 and SLC7A9. These genes also give instructions for the absorption of other amino acids, such as lysine and arginine
- Cystinuria results from the mutation of these genes. There are 3 types of cystinuria:
- Type I and II: Normal amounts of cystine are present in the urine. Type I is the most common type
- Type III: Cystine levels in blood increase after cystine administration, which means that the kidneys improperly filter cystine
- Cystinuria may also be categorized as infantile, juvenile, and adolescent, indicating when symptoms first begin to appear
- The Cystine Urine Test helps determine the levels of cystine and similar amino acids, such as lysine and arginine, in urine. It is used to diagnose cystinuria
Note: The levels are compared to levels of creatinine, a reliable reference compound.
What are the Clinical Indications for performing the Cystine Urine Test?
Following are the clinical indications for performing the Cystine Urine Test:
- Family history of cystinuria
- Dull pain in the upper back
- Discolored urine
- Trouble urinating
- Abnormally frequent or infrequent urination
How is the Specimen Collected for the Cystine Urine Test?
Following is the specimen collection process for Cystine Urine Test:
Sample required: Urine
Process of obtaining a sample in adults: Urination into a sterile container over a 24-hour period.
Preparation required: It is recommended to drink 6 to 8 glasses of water or other fluids prior to the test.
What is the Significance of the Cystine Urine Test Result?
A high value for the Cystine Urine Test is associated with the age of the individual and is as follows:
- Age 0-5 months (in µmol/g)
- Arginine - greater than 124
- Cystine - greater than 345
- Lysine - greater than 1761
- Ornithine - greater than 168
- Age 6-11 months (in µmol/g)
- Arginine - greater than 97
- Cystine - greater than 133
- Lysine - greater than 699
- Ornithine - greater than 71
- Age 1-3 years (in µmol/g)
- Arginine - greater than 80
- Cystine - greater than 186
- Lysine - greater than 611
- Ornithine - greater than 71
- Age 4-12 years (in µmol/g)
- Arginine - greater than 72
- Cystine - greater than 106
- Lysine - greater than 602
- Ornithine - greater than 62
A high value for the Cystine Urine Test, as shown by the above values, may indicate:
- Nephrotoxicity due to heavy metals
- Renal tubular acidosis
- Wilson disease
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information:
- Certain factors, such as pregnancy, may interfere with the results of the Cystine Urine Test
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.
What are some Useful Resources for Additional Information?
The following DoveMed website link is a useful resource for additional information:
Please visit our Laboratory Procedures Center for more physician-approved health information:
References and Information Sources used for the Article:
Ahmed, K., Dasgupta, P., & Khan, M. S. (2006). Cystine calculi: challenging group of stones.Postgraduate Medical Journal, 82(974), 799-801.
Kee, J. L. (2010). Laboratory and diagnostic tests with nursing implications (8th ed.). Upper Saddle River, NJ: Pearson.
Martini, F., Nath, J. L., & Bartholomew, E. F. (2012). Fundamentals of anatomy & physiology (9th ed.). San Francisco: Benjamin Cummings.
Schnell, Z. B., Van, L. A., & Kranpitz, T. R. (2003). Davis's Comprehensive handbook of laboratory and diagnostic tests: With nursing implications. Philadelphia: F.A. Davis.
Williamson, M. A., Snyder, L. M., & Wallach, J. B. (2011). Wallach's interpretation of diagnostic tests (9th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins.