If your patient complains of diarrhea, bloody mucous stools, or abdominal cramps and he has recently returned from the tropics, immediately consider amebic colitis. Warm wet-field fecal smears and cultures can aid diagnosis, but the microscope method is quicker and more accurate.
If you find mucosal ulcers during a sigmoidoscopic or proctoscopic examination, make direct mucosal smears of the of the ulcer margin and examine them microscopically. Look for Entamoeba histolytica, a mobile trophozoite, 6 microns to 40 microns in diameter, with clear hyaline unidirectional pseudopods containing ingested red blood cells. E histolytica may be confused with Escherichia coli, the normal inhabitant of the intestine, except that E coli never contain phagocytized red blood cells.