**Question:** Anti DNAase-B is used for diagnosis of -

A. Cystic Fibrosis (CF)
B. Chronic Obstructive Pulmonary Disease (COPD)
C. Chronic Granulomatous Disease (CGD)
D. Neonatal Severe Acute Respiratory Distress Syndrome (SARDS)

**Core Concept:**
Anti DNAse-B is a specific enzyme test used for diagnosing Chronic Granulomatous Disease (CGD). DNAse-B is an enzyme produced by neutrophils, which breaks down DNA in the phagolysosome during the immune response. In CGD, the phagolysosome fails to break down DNA, leading to the accumulation of DNA in neutrophils and monocytes. Anti DNAse-B test detects the presence of anti-DNAse-B antibodies in the patient's serum.

**Why the Correct Answer is Right:**
Anti DNAse-B is a specific test for diagnosing CGD because neutrophils in healthy individuals break down DNA in the phagolysosome. In CGD patients, neutrophils and monocytes accumulate extracellular DNA due to the deficiency of NADPH oxidase enzyme complex and the inability to produce reactive oxygen species. This leads to the production of anti-DNAse-B antibodies in response to the accumulated extracellular DNA. When these antibodies bind to DNA, they form a precipitate that can be detected by the test.

**Why Each Wrong Option is Incorrect:**

A. Cystic Fibrosis (CF) does not affect DNAse-B activity. DNAse-B deficiency is a rare cause of recurrent respiratory infections, but CF is a common genetic disorder causing chronic pulmonary infections due to impaired mucus clearance and altered immune response.

B. Chronic Obstructive Pulmonary Disease (COPD) is a smoking-related disease with airway inflammation and narrowing, leading to breathlessness and chronic bronchitis. It does not involve DNAse-B deficiency or accumulation of extracellular DNA.

C. Neutrophils are essential for the immune response and phagocytosis, and DNAse-B deficiency can lead to recurrent infections. However, the correct answer is CGD, not DNAse-B deficiency, as explained above.

D. Neonatal Severe Acute Respiratory Distress Syndrome (SARDS) is a rare condition in premature infants and is unrelated to DNAse-B deficiency or extracellular DNA accumulation. The correct answer is CGD, which also affects premature infants, but due to DNAse-B deficiency and extracellular DNA accumulation.

**Clinical Pearl:**

CGD is a rare autosomal recessive disorder affecting neutrophils, macrophages, and eosinophils. Children with CGD are prone to recurrent bacterial and fungal infections, particularly affecting the respiratory, gastrointestinal, and genitourinary systems. Diagnosis is often delayed due to the overlap of symptoms with other diseases. Hence, a high index of suspicion is required when dealing with recurrent infections in children.