Amebiasis: Diagnosis 

Diagnosis of amebiasis is complicated, partly because the disease  can affect several areas of the body  and can range from exhibiting few, if any, symptoms  to being severe, or even life-threatening. In most cases, a physician will consider a diagnosis of amebiasis  when a patient has a combination of symptoms, in particular, diarrhea and a possible history of recent exposure to amebiasis through travel, contact  with infected persons, or anal intercourse. 

It is vital to distinguish between amebiasis  and another disease, inflammatory bowel disease (IBD) that produces similar symptoms because, if diagnosed incorrectly, drugs that are given to treat IBD can encourage the growth and spread of the amebiasis organism. Because of the serious consequences of misdiagnosis, potential cases of IBD must be confirmed with multiple stool samples and blood tests, and a procedure involving a visual inspection of the intestinal wall using a thin lighted, tubular instrument (sigmoidoscopy) to rule out amebiasis. 

A diagnosis of amebiasis may be confirmed by one or  more tests, depending on  the location of the disease. 

Stool examination
This test involves microscopically examining a stool sample for the presence of cysts and/or trophozoites of E. histolytica  and not one of the many other intestinal amebas  that are often found  but that  do not cause disease. A series of three stool  tests is approximately 90% accurate in confirming  a diagnosis of amebic dysentery. Unfortunately, however, the stool test  is not useful in diagnosing amebomas or extraintestinal infections. 

Sigmoidoscopy 

Sigmoidoscopy  is a useful diagnostic procedure in which a thin, flexible, lighted instrument, called a sigmoidoscope,  is used to visually examine  the lower part  of the large intestine for amebic ulcers and take tissue  or fluid samples from  the intestinal lining. 

Blood tests 

Although tests designed to detect a specific protein produced in response to amebiasis infection (antibody) are capable of detecting only about 10% of cases of mild amebiasis, these tests are extremely useful in confirming 95% of dysentery diagnoses and 98% of liver abscess diagnoses. Blood serum will usually  test positive for antibody within a week of symptom onset. Blood testing, however, cannot always distinguish between a current or past infection since the antibodies  may be detectable  in the blood for as long as 10 years following initial infection. 

Imaging studies 
A number of sophisticated imaging techniques, such as computed tomography scans (CT), magnetic resonance imaging (MRI), and ultrasound, can be used to determine whether a liver abscess is present. Once located, a physician may then use a fine needle to withdraw a sample of tissue to determine whether the abscess is indeed caused by an amebic infection.