A man presented with diarrhea and lower abdominal pain. The stool is heme-positive. Investigation of choice for amoebiasis is?
**Core Concept**
The patient's presentation of diarrhea, lower abdominal pain, and heme-positive stool suggests intestinal infection, specifically amoebiasis caused by Entamoeba histolytica. This parasitic infection leads to colitis, which can be acute or chronic.
**Why the Correct Answer is Right**
The investigation of choice for amoebiasis is the stool antigen test, which detects specific antigens of Entamoeba histolytica in the stool. This test is highly sensitive and specific, allowing for accurate diagnosis. The stool antigen test works by targeting the galactose-inhibitable adherence lectin (GIAL) found on the surface of E. histolytica trophozoites. This protein is a specific marker for the pathogen, making it an ideal target for detection.
**Why Each Wrong Option is Incorrect**
* **Option A:** Stool culture is not a preferred method for diagnosing amoebiasis because it is time-consuming, requires specialized media, and may not always yield a positive result.
* **Option B:** Colonoscopy may be useful for evaluating the extent of intestinal damage but is not the primary diagnostic tool for amoebiasis.
* **Option D:** Stool examination for ova and parasites (O&P) may show the presence of E. histolytica cysts or trophozoites but is less sensitive and specific than the stool antigen test.
**Clinical Pearl / High-Yield Fact**
The stool antigen test is a rapid and reliable diagnostic tool for amoebiasis, making it an essential test for patients with suggestive symptoms.
**Correct Answer:** C.