Question

What is the investigation of choice for invasive amebiasis?

• A. ELISA
• B. Biopsy
• C. IHA (Indirect Haemagglutination Assay)
• D. PCR

Hint:

Stool exam is often negative once the amoeba invades tissue, so serology becomes the test of choice.

Answer 1

The Correct Option is A

This question checks which test correctly picks up amebiasis after it has left the gut and invaded tissue, such as in an amebic liver abscess.

1. ELISA: Detects antibodies the body makes against Entamoeba histolytica once it invades tissue. It is highly sensitive, becomes positive early, and does not depend on finding the parasite in stool, which makes it the right choice here.
2. Biopsy: Can show trophozoites directly in tissue, but getting a sample means an invasive procedure such as colonoscopy or image guided aspiration, which is riskier and not the first test ordered.
3. IHA: Also an antibody test, but it is less sensitive than ELISA and can stay positive for years after old, cured infections, so a positive result does not confirm current disease.
4. PCR: Useful on stool to confirm the parasite and separate it from the non-invasive look alike species, but it is built for luminal infection, not for diagnosing disease that has already spread into tissue.

Because invasive disease often clears the gut lumen of trophozoites, an antibody-based test is needed, and ELISA gives the best sensitivity of the antibody tests available. So the correct answer is ELISA.

Let's summarize:

• Stool microscopy is unreliable once amebiasis becomes invasive.
• ELISA detects antibodies with high sensitivity and is the modern serologic test of choice.
• IHA is an older, less sensitive antibody test that cannot separate old from new infection.

The investigation of choice for invasive amebiasis is ELISA.