Test Update Memorandum – White Blood Cell Cystine

The Baylor Medical Genetics Laboratories are constantly striving to improve our services to the clinical community. On March 12, 2013, our biochemical laboratory started to use an optimized protocol for cystine determination in white blood cells for test code 4627. Cystine is a highly labile compound, and its level is subject to sample shipping and handling. This protocol change minimizes the loss of cystine during sample preparation. The normal cystine range is not affected by this change; however, as a result of the protocol change, the cystine level reported may be
increased in cystinosis patients. This apparently elevated level may lead to concern for patient non-compliance when compared with previous results. Please take this method change into consideration when monitoring the patient’s cystine levels.