Entamoeba histolytica (amoebiasis) antibody

Doctors advise an E. histolytica antibody test when the parasite is not detected in the stool sample under a microscope even though the person has apparent symptoms indicative of amoebiasis. This condition usually occurs when the infection appears to be outside the intestines such as in the liver, lungs, or brain. 

The following symptoms may prompt a doctor to order this test:

• Watery stools or stools mixed with blood
• Severe cramps or pain in the abdomen
• Bloating sensation due to gases in the abdomen
• Rise in the body temperature or high fever, especially in case of liver abscess, infection of lungs or brain.

For complete diagnosis and to confirm for the spread of the pathogen in the liver, lungs and brain, your doctor may also order other tests such as complete blood count, erythrocyte sedimentation rate, computed tomography and magnetic resonance imaging.

No preparations are required before this test.

A lab technician will collect a small amount of blood from a vein in your arm and store it in a gold-top tube. It is a specialised tube, which contains a chemical (clot activator) that separates red blood cells from the fluid in the blood and eases the identification of antibodies later. The tube is then moved to the laboratory for further analysis. 

At the lab, a fluorescent enzyme is added to the sample, which changes colour when it reacts with anti-E.hystolitica antibodies. Based on this principle and a few other factors, various techniques are used to detect the antibodies in a blood sample. These include indirect haemagglutination assay, counterimmunoelectrophoresis, amoebic gel diffusion test, complement fixation, indirect fluorescence assay, latex agglutination and enzyme-linked immunosorbent assay (ELISA). 

ELISA is the most commonly used technique as it takes less time and is not as costly. Sometimes, enzyme immunoassay (EIA) technique, which is similar to the ELISA technique, is also used to detect E. histolytica antibodies.

The complete procedure takes one to five days by ELISA and two hours by EIA. The test is repeated after seven days if antibodies are not detected despite the presence of amoebiasis symptoms.

Normal results: 

• Negative test: <1:32 or 8 U or <8 U indicates IgG E. histolytica antibodies are not detected.
• Equivocal: 9-11 U indicate that titres are doubtful for the presence of antibodies. Repeat the test after 10-14 days.

Abnormal results:

• Positive test: >1:128 or 12 U or >12 U indicates the presence of IgG E. histolytica antibodies in the body and suggests amoebiasis.

However, positive results do not clarify whether the infection is active at present or had occurred in the past. The antibodies are present in the blood for a long time - up to a few years - even after the infection is completely cured.

The test detects the E. histolytica antibodies in 95% cases of infection that occurs in organs other than intestines (liver, lungs, brain, etc.), 70% of cases with an active infection in the intestines and 10% of carrier cases who do not suffer from the symptoms of amoebiasis.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.