Diagnostic Testing for Chronic Granulomatous Disease

Chronic granulomatous disease (CGD) is a rare genetic immunodeficiency associated with recurrent bacterial infections, granulomas, and increased mortality. It is characterized by the inability of phagocytes (neutrophils, monocytes, etc.) to generate reactive oxygen species (ROS), a major component of the microbicidal repertoire of phagocytes. Diagnosis of patients with CGD is commonly based on the assessment of ROS production by neutrophils. Multiple assays to assess ROS production are described-a flow cytometric dihydrorhodamine assay and a histochemical nitroblue tetrazolium assay, both of which can be used to visualize ROS production in individual cells, and two quantitative assays-O₂^˙- reduction of ferricytochrome c and a ROS-dependent, luminol-enhanced chemiluminescence assay that will quantitate the response of a population of cells. In addition, two approaches to identify the defective phox protein defect are described-standard immunoblotting and flow cytometry of neutrophils stained with phox-specific antibodies. When determining the status of a patient, several assays should be used to assess ROS production and identify the protein defect. The results of these assays should agree and can be used to develop a comprehensive package, which includes confirmation of a diagnosis of CGD, identification of the specific protein target for genetic sequencing, and an indication of the prognosis for the patient.