Diagnosis and Monitoring of Cystinosis Using Immunomagnetically Purified Granulocytes.

Background: Cystine determination is a critical biochemical test for the diagnosis and therapeutic monitoring of the lysosomal storage disease cystinosis. The classical mixed-leukocyte cystine assay requires prompt specialized recovery/isolation following blood drawing, providing cystine concentrations normalized to total protein from assorted types of white blood cells, each with varying cystine content.

Methods: We present a new workflow for cystine determination using immunomagnetic granulocyte purification, and new reference ranges established from 47 patient and 27 obligate heterozygote samples assayed.