In chronic granulomatous disease, which laboratory finding is characteristic?

• A. Positive nitroblue tetrazolium test
• B. Normal respiratory burst
• C. Reduced lactoferrin levels
• D. Negative nitroblue tetrazolium test

Answer: (D)

In chronic granulomatous disease the key issue is a defective respiratory burst in phagocytes due to an NADPH oxidase defect. This means neutrophils can’t produce the reactive oxygen species needed to kill ingested microbes. The nitroblue tetrazolium test relies on this burst: normal neutrophils reduce NBT to a blue formazan pigment, staining cells blue. In CGD, the oxidative burst is absent or reduced, so little or no formazan forms and the test remains colorless—negative. That’s why a negative nitroblue tetrazolium test is characteristic.

The other ideas don’t fit CGD: a positive NBT would imply a normal burst, which CGD lacks; a normal respiratory burst is incorrect for CGD; lactoferrin levels aren’t diagnostic for CGD and don’t define the condition. Modern testing often uses the dihydrorhodamine flow cytometry assay, which shows diminished green fluorescence in CGD.