Which diagnostic test is primarily used to evaluate NADPH oxidase activity?

The primary diagnostic test used to evaluate NADPH oxidase activity is the Dihydrorhodamine 123 test. This test measures the ability of phagocytes to produce reactive oxygen species (ROS) through NADPH oxidase during the respiratory burst, a critical function of these immune cells in combating infections. When phagocytes are stimulated, NADPH oxidase generates superoxide anion, which then converts dihydrorhodamine 123 into a fluorescent compound, allowing for quantification through flow cytometry.

Using this test provides a clear indication of the functional status of NADPH oxidase. In patients with Chronic Granulomatous Disease (CGD), a genetic disorder affecting NADPH oxidase, this test will show significantly reduced or absent fluorescence, indicating the inability of their phagocytes to produce the necessary oxidative burst.

While the other tests mentioned have their specific applications—flow cytometry is a method for analyzing cell populations, the immunofluorescence assay is used to detect specific proteins in cells, and the NBT test is also used to assess oxidative burst activity—they are not as direct or definitive in evaluating NADPH oxidase activity compared to the Dihydrorhodamine 123 test. Thus, this test stands out