Diagnosis and Testing
How do I get tested for cystinosis?
Nephropathic cystinosis should be suspected in a child who does not grow and gain weight very well and who has symptoms of renal Fanconi syndrome. These symptoms include urinating a lot, passing large amounts of urine, and losing large amounts of minerals and electrolytes through the urine. A urine sample can be tested to detect minerals, electrolytes, amino acids, and carnitine. The urine may also contain a lot of water. An early diagnosis of nephropathic cystinosis is important because drugs that lower the cystine levels in the body can slow or prevent specific symptoms.
There are three main tests that can help to confirm a diagnosis of nephropathic cystinosis:
- Cystine concentrations can be measured in specific white blood cells called polymorphonuclear leukocytes (LCL). Elevated levels of cystine indicate cystinosis.
- Cystine crystals can be seen in the eyes through a slit lamp, which is a specialized microscope that allows an eye doctor to look at the eyes under high magnification.
- Molecular genetic testing can find the gene changes that cause cystinosis. There are different ways this testing can be done.
Measuring cystine levels in white blood cells and molecular genetic testing will require samples to be sent to a dedicated laboratory that performs such tests. Detection of cystine crystals in the eyes may require referral to an experienced eye doctor. The easiest way to begin testing for cystinosis is to discuss it with the pediatrician or primary doctor. A list of doctors who specialize in cystinosis can be found on the Cystinosis Research Network Expert doctor list. Testing information in your area can also be obtained through a genetic counselor, to find a genetic counselor visit the National Society of Genetic Counselors Find a Genetic Counselor website.
Besouw MTP, Levtchenko EN. Improving the prognosis of nephropathic cystinosis. Int J Nephrol Renovasc Dis. 2014; 7: 297-302. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4109637/ Accessed March 22, 2016.
Nesterova G, Gahl WA. Cystinosis. GeneReviews website. http://www.ncbi.nlm.nih.gov/books/NBK1400/ Updated January 30, 2014. Accessed March 22, 2016.
Emma F, Nesterova G, Langman C. Nephropathic cystinosis: an international consensus document. Nephrol Dial Transplant. 2014;29(Suppl 4):87-94. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4158338/ Accessed March 22, 2016.