Which test for CGD diagnosis is mostly a qualitative measurement of NADPH oxidase activity?

The NBT (nitroblue tetrazolium) test is primarily a qualitative measurement of NADPH oxidase activity, specifically assessing the capacity of neutrophils to produce reactive oxygen species (ROS). In patients with Chronic Granulomatous Disease (CGD), there is a defect in the NADPH oxidase enzyme complex, which leads to an inability of phagocytes to generate superoxide and other ROS. During the NBT test, neutrophils are stimulated, and in normal individuals, they will reduce NBT to formazan, indicating the presence of functioning NADPH oxidase activity. Conversely, in individuals with CGD, there is a lack of color change, demonstrating the impaired ability to produce the ROS necessary for NBT reduction.

While other tests, such as flow cytometry and dihydrorhodamine 123, also assess oxidative burst activity and may provide more quantitative results, the NBT test's primary function as a qualitative measure of NADPH oxidase activity in the context of CGD diagnosis makes it stand out. Therefore, the specificity of the NBT test in evaluating the functional defect inherent in CGD is pivotal for diagnosis and understanding the underlying pathophysiology of the disease.