Nitroblue tetrazolium test is used for?
**Core Concept**
The Nitroblue tetrazolium (NBT) test is a diagnostic tool used to assess the function of phagocytic cells, specifically the ability of neutrophils to produce superoxides through the respiratory burst process. This process is essential for the killing of ingested microbes.
**Why the Correct Answer is Right**
The NBT test works by measuring the reduction of nitroblue tetrazolium to a blue formazan product, which is indicative of superoxide production. Neutrophils that are able to produce superoxides will reduce the NBT, resulting in a blue color. This reaction is catalyzed by the enzyme NADPH oxidase, which is crucial for the respiratory burst process. A deficiency in NADPH oxidase, such as in chronic granulomatous disease (CGD), will result in a negative NBT test.
**Why Each Wrong Option is Incorrect**
**Option A:** The NBT test is not used to diagnose autoimmune disorders like Systemic Lupus Erythematosus (SLE). While SLE can affect phagocytic cells, the NBT test is not a diagnostic tool for this condition.
**Option B:** The NBT test is not a measure of neutrophil count or differential. It is a functional assay that assesses the ability of neutrophils to produce superoxides.
**Option C:** The NBT test is not used to diagnose infections like tuberculosis. While neutrophils play a role in the immune response to infections, the NBT test is not a diagnostic tool for specific infections.
**Clinical Pearl / High-Yield Fact**
A negative NBT test is suggestive of chronic granulomatous disease (CGD), a rare genetic disorder characterized by recurrent infections and granulomatous inflammation. CGD is caused by a deficiency in the NADPH oxidase enzyme, which is essential for the respiratory burst process.
**Correct Answer: C. Diagnosing chronic granulomatous disease (CGD).**