Post streptococcal glomerulonephritis in children is diagnosed by:
**Core Concept**
Post streptococcal glomerulonephritis (PSGN) is an immune complex-mediated glomerulonephritis that occurs following streptococcal infection, typically after a throat or skin infection. It is characterized by the deposition of immune complexes in the glomeruli, leading to inflammation and damage.
**Why the Correct Answer is Right**
The correct answer is based on the presence of specific antibodies in the blood that are directed against the streptococcal antigens. The diagnosis of PSGN is typically made by detecting the presence of anti-streptolysin O (ASO) or anti-DNAse B antibodies, which are indicative of a recent streptococcal infection. These antibodies are produced in response to the infection and can be detected in the blood for several weeks after the infection has resolved. The presence of these antibodies helps to confirm the diagnosis of PSGN and distinguishes it from other forms of glomerulonephritis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because serum C3 levels are often decreased in PSGN, but this is not a specific or sensitive diagnostic criterion.
**Option B:** This option is incorrect because while a throat culture may be positive for streptococci, it is not a specific diagnostic test for PSGN.
**Option C:** This option is incorrect because while a urine culture may be positive for bacteria, it is not a diagnostic test for PSGN.
**Clinical Pearl / High-Yield Fact**
In children, PSGN typically presents with hematuria, proteinuria, and hypertension, and is often preceded by a sore throat. The diagnosis of PSGN should be considered in any child who presents with these symptoms and has a recent history of streptococcal infection.
**Correct Answer:** D. Elevated anti-streptolysin O (ASO) or anti-DNAse B antibodies.