A man presented with diarrhea and lower abdominal pain. The stool is heme-positive. Investigation of choice for amoebiasis is?

Amebiasis is infection with the parasitic intestinal protozoan Entamoeba histolytica (the "tissue-lysing ameba"). The most common extraintestinal manifestation of amebiasis is amebic liver abscess. Microscopy, often combined with enzyme-linked immunosorbent assays (ELISAs), remains the standard diagnostic approach. Ref: Stanley, S.L. (2012). Chapter 209. Amebiasis and Infection With Free-Living Amebas. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.