Nitroblue tetrazolium test is used for:
**Core Concept**
The nitroblue tetrazolium (NBT) test is a diagnostic tool used to measure the activity of superoxide anion-producing cells, such as neutrophils. It is based on the ability of these cells to reduce nitroblue tetrazolium to formazan, which is a blue-colored compound that can be visually detected.
**Why the Correct Answer is Right**
The NBT test is used to assess the function of the NADPH oxidase enzyme system in phagocytic cells, such as neutrophils and macrophages. This enzyme system is responsible for producing superoxide anions, which are crucial for killing ingested microorganisms. In patients with chronic granulomatous disease (CGD), the NADPH oxidase enzyme system is defective, leading to impaired superoxide production and a positive NBT test result. The test is therefore used to diagnose CGD and other disorders of phagocytic cell function.
**Why Each Wrong Option is Incorrect**
**Option A:** The NBT test is not used to diagnose diabetes mellitus.
**Option B:** The test is not a measure of lymphocyte function.
**Option C:** The NBT test is not used to assess platelet function.
**Clinical Pearl / High-Yield Fact**
The NBT test is a useful diagnostic tool for identifying patients with chronic granulomatous disease (CGD), a rare genetic disorder characterized by impaired superoxide production and recurrent infections.
**Correct Answer:** D. Diagnosing chronic granulomatous disease (CGD).