White Blood Cell Cystine Testing

Track your cystine with regular white blood cell (WBC) cystine testing

Along with careful adherence to a treatment plan, testing your WBC cysteine accumulation on a regular basis is one of the most important habits to build when trying to manage cystinosis. WBC cystine testing helps you see changes in your cystine accumulation, which in turn helps you and your doctor determine how well cystine is being depleted and whether your medication dosages need to be adjusted.1 Since controlling cystine concentration is the only way to limit or prevent organ and tissue damage, it is essential to know if your medication or therapy is working the way it should be.2

There are currently two forms of of WBC testing available: mixed leukocyte testing and granulocyte testing. Until recently, all WBC testing for the diagnosis of cystinosis and the monitoring of cystine levels was mixed leukocyte testing. However, recently a new method of granulocyte testing has been developed and, because cystine preferentially accumulates in the granulocyte cells, this test may provide alternative results.4,5 Please be sure you know which test was used when measuring your WBC levels as the ranges differ depending on the test.

NOTE: The biggest drop in your WBC cystine levels may occur immediately after your previous dose and may cause inaccurate test results. Consult your doctor for the best time frame for your test.1

 

Definitions

Leukocytes: better known as white blood cells and help fight infection3
Granulocytes: a category of leukocytes that contain granules in their cytoplasm3

Types of Testing

Mixed leukocyte: This method requires isolation of leukocytes immediately after the blood is drawn.4

Granulocyte: This method requires that the whole blood sample be sent refrigerated to the lab within a certain time frame for analysis.4

A difference between the two tests is how the blood is processed. While mixed leukocyte testing looks at  the cystine buildup in all WBCs, granulocyte testing looks at the cystine buildup in solely granulocyte cells.4,5

It is important to remember to consult with your doctor about which test he or she recommends.
WBC cystine testing is important even if you’ve had a kidney transplant and even if you look or feel fine. Even brief interruptions in your cystine-depleting therapy allow cystine accumulation to become toxic again.6-10 The goal of cystine-depleting medications is to keep your cystine levels down, so be sure to consult with your doctor and laboratory for the recommended target values.7,11 To achieve continuous cystine control, regular WBC cystine tests may be needed as often as every 3 months and sometimes more frequently.12

The good news is that testing your WBC cystine accumulation is a procedure requiring only a blood sample.1 Because the test is so important, it’s a good idea to make regular testing a part of your cystinosis management plan. WBC cysteine testing gives you and your doctor more knowledge and information, which can enable optimal dosing and empower new strategies to help you stay one step ahead of cystinosis.

References

  1. Dalton N. The importance of accurate cystine level testing. Cystinosis Research Network Web site. https://cystinosis.org/images/research/articlelibrary/cystagon/2009_01_Cystine_Level_Testing.pdf. Published January 2009. Accessed September 23, 2016.
  2. National Organization for Rare Disorders. Cystinosis. NORD Web site. https://rarediseases.org/rare-diseases/cystinosis. Accessed August 20, 2016.
  3. Merriam-Webster: dictionary and thesaurus. Merriam-Webster Web site. http://merriam-webster.com. Accessed October 5, 2016.
  4. UCSD Cystine Determination Laboratory. UCSD Web site. http://cystinosiscentral.org/cystinosis/tests. Accessed September 23, 2016.
  5. Levtchenko E, de Graaf-Hess A, Wilmer M, van den Heuvel L, Monnens L, Blom H. Comparison of cystine determination in mixed leukocytes vs polymorphonuclear leukocytes for diagnosis of cystinosis and monitoring of cysteamine therapy. Clin Chem. 2004;50(9):1686-2688.
  6. Brodin-Sartorius A, Tète M-J, Niaudet P, et al. Cysteamine therapy delays the progression of nephropathic cystinosis in late adolescents and adults. Kidney Int. 2012;81(2):179-189.
  7. Gahl WA, Thoene JG, Schneider JA. Cystinosis. N Engl J Med. 2002;347(2):111-121.
  8. Gahl WA, Balog JZ, Kleta R. Nephropathic cystinosis in adults: natural history and effects of oral cysteamine therapy. Ann Intern Med. 2007;147(4):242-250.
  9. Levtchenko EN, van Dael CM, de Graaf-Hess AC, et al. Strict cysteamine dose regimen is required to prevent nocturnal cystine accumulation in cystinosis. Pediatr Nephrol. 2006;21(1):110-113.
  10. Nesterova G, Gahl WA. Cystinosis: the evolution of a treatable disease. Pediatr Nephrol. 2013;28(1):51-59.
  11. Gertsman I, Johnson WS, Nishikawa C, Gangoiti JA, Holmes B, Barshop BA. Diagnosis and monitoring of cystinosis using immunomagnetically purified granulocytes. Clin Chem. 2016;62(5):766-772.
  12. Cystinosis Research Network. Need a white blood cell cystine level? CRN Web site. https://cystinosis.org/images/family-support/resources/medical-information/CYS.WBCP.UK.pdf. Published 2009. Accessed August 21, 2016.