**Question:** Investigation of choice for invasive amebiasis is:

A. Serological tests
B. Stool examination
C. Radiological studies
D. Biopsy

**Correct Answer:** B. Stool examination

**Core Concept:**
Amebiasis is an infectious disease caused by the protozoan parasite Entamoeba histolytica. Invasive amebiasis refers to the more severe form of the disease where the parasite causes tissue destruction, leading to complications like abscesses, fistulae, or cholangitis. Diagnosis of invasive amebiasis requires identifying the parasite in a sample to confirm the infection.

**Why the Correct Answer is Right:** Stool examination is the most appropriate investigation for invasive amebiasis due to the following reasons:

1. **Direct microscopic examination:** This method involves searching for ova, cysts, or trophozoites of Entamoeba histolytica in a stool sample. Direct examination is the gold standard for diagnosing amebiasis.

2. **Culture methods:** These methods involve growing Entamoeba histolytica in a laboratory setting. While culture methods are more sensitive than direct examination, they are less specific and require advanced laboratory facilities.

3. **Serological tests:** These tests detect antibodies produced in response to the infection. Serological tests are less specific for invasive amebiasis due to cross-reactivity with other parasitic infections.

4. **Radiological studies:** Radiological studies like X-rays or CT scans are used to detect complications like abscesses, fistulae, or cholangitis. They provide information on the location and extent of the infection but do not confirm the presence of the parasite itself.

**Why Each Wrong Option is Incorrect:**

A. Serological tests: As mentioned earlier, serological tests are less specific for invasive amebiasis due to cross-reactivity with other parasitic infections.

B. Biopsy: A biopsy is usually performed to confirm tissue involvement in suspected invasive amebiasis, not for primary diagnosis. Stool examination remains the gold standard for confirming the presence of Entamoeba histolytica.

C. Radiological studies: Although radiological studies are essential for detecting complications, they do not confirm the presence of the parasite itself. Stool examination remains the primary investigation for diagnosing amebiasis.

**Clinical Pearl:**

When considering invasive amebiasis, clinical suspicion is crucial, as the disease often presents with nonspecific symptoms like fever, abdominal pain, and diarrhea. Stool examination with direct microscopic examination or culture methods is essential to confirm the presence of Entamoeba histolytica and initiate appropriate treatment. Radiological studies are helpful for detecting complications, but stool examination is crucial for diagnosis. Serological tests are less specific due to cross-reactivity with other parasitic infections. Biopsy is performed for tissue involvement confirmation, not for primary diagnosis.