Streptococcal GN is best diagnosed by -a) ASO titreb) AntiDNAsec) Antihyaluronidase d) Culture

**Core Concept**
Streptococcal glomerulonephritis (GN) is an immune-mediated disease following streptococcal infection, often diagnosed through serological tests. The underlying principle involves the detection of antibodies produced in response to streptococcal antigens. **Antistreptolysin O (ASO) titer** is a key serological marker.

**Why the Correct Answer is Right**
The correct answer is related to the detection of antibodies against streptococcal infections. **ASO titer** is elevated in response to streptococcal infections, particularly those caused by **Group A beta-hemolytic streptococci**, which are often implicated in streptococcal GN. This test measures the level of antibodies against streptolysin O, an enzyme produced by streptococci.

**Why Each Wrong Option is Incorrect**
**Option B:** Anti-DNAse is another antibody that can be elevated in streptococcal infections but is not the best diagnostic marker for streptococcal GN.
**Option C:** Antihyaluronidase is also an antibody against a streptococcal enzyme, but it is less commonly used for diagnosis compared to ASO titer.
**Option D:** Culture is not typically used for diagnosing streptococcal GN because the infection has usually resolved by the time renal symptoms appear.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **ASO titer** can be negative in some cases of streptococcal GN, especially if the infection is caused by a strain that does not produce streptolysin O. However, it remains a valuable diagnostic tool in the appropriate clinical context.

**Correct Answer:** A. ASO titer