Entamoeba histolytica (Amebiasis) – Serology

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides specific testing information for the serological diagnosis of invasive extraintestinal amebiasis at Public Health Ontario (PHO). The causative agent of amebiasis is the parasitic amoeba Entamoeba histolytica.

Updates
As of October 15, 2025, this webpage was updated to include background, testing indications, acceptance criteria, referred out test methodology, performance and limitations, interpretations, and expected turnaround times based on calendar days instead of business days.

*Uncontrolled print copy. Valid only on day of print: 17 Oct 2025.

Testing Indications

E. histolytica serology is only indicated in individuals with suspected extraintestinal amebiasis (e.g. amebic liver abscess). In addition, microscopy or PCR of implicated tissue materials (e.g. abscess aspirate) is recommended where feasible. Note: serology is NOT indicated for localized intestinal infections; stool testing should be performed in these situations instead.¹

Acceptance/Rejection Criteria

Requests without clinical information mentioning the extraintestinal presentation (e.g. “extraintestinal”, “abscess”, or “ulcer”) will be cancelled.

Specimen Collection and Handling

Specimen Requirements

Test Requested

Required Requisition(s)

Specimen Type

Minimum Volume

Collection Kit

Entamoeba histolytica serology

General Test Requisition

Serum, or

Blood, clotted

1.0ml

5.0 ml

Serum separator tube (SST), or Plain or pro-coagulation tube

Submission and Collection Notes

Complete all fields of the requisition form.

Specify the extraintestinal nature of the illness on the requisition (e.g. “extraintestinal”, “abscess”, “ulcer”).

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

If the patient is part of a cluster/outbreak investigation, contact PHO Laboratory Customer Service at 416-235-6556/1-877-604-4567 prior to sample submission.

Timing of Specimen Collection

Serology may be negative in the first 7 to 14 days from symptom onset; repeat testing after 14 days from symptom onset may be indicated if extraintestinal amebiasis is strongly suspected.

In some circumstances (e.g., to differentiate acute from remote infection), it may be useful to compare the titres of antibodies in paired serum specimens. If needed, contact PHO Laboratory Customer Service at 416-235-6556/1-877-604-4567 prior to sample submission.

Storage and Transport

Centrifuge tube if using serum separator tube (SST). Place specimen container in a biohazard bag and properly seal the bag. Specimens should be stored at 2-8°C and shipped to PHO on ice packs within 48 hours of collection. All specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Serology is performed weekly at the National Reference Centre for Parasitology (NRCP) in Montreal. Turnaround time is up to 14 calendar days from receipt at PHO’s laboratory.

Stat and Critical Specimens Testing

Priority testing for extraintestinal amebiasis is available upon request. If needed, contact PHO Laboratory Customer Service at 416-235-6556/1-877-604-4567 prior to sample submission.

Test Methods

E. histolytica serology is performed at the NRCP using an enzyme-linked immunosorbent assay (ELISA) based on antibody capture using antigens of the E. histolytica strain NIH-200.

Performance and Limitations:
The NRCP reports a sensitivity above 95% for extraintestinal amebiasis and a specificity of 92%. With other assays, E. histolytica serology has a reported sensitivity of around 95% for extraintestinal amebiasis and specificity above 90%.¹ However, antibody titres may take 7 to 14 days to develop and may persist for years after resolution of the infection. Therefore, a negative result in acute illness does not rule out infection, and a single positive result cannot distinguish current from resolved or past infection. Note: Serology is poorly sensitive (≤ 70%) for invasive intestinal amebiasis, therefore stool testing is preferrable over serology for individuals without extraintestinal manifestations.

Algorithm

Entamoeba histolytica serology by EIA:

Optical Density (OD) Sample Value	Result	Interpretation
≥ 1.20	High Positive	E. histolytica antibodies detected. Does not distinguish current from resolved or past infection. Clinical correlation required.
0.45-1.19	Low Positive	E. histolytica antibodies detected. Does not distinguish current from resolved or past infection. Clinical correlation required.
0.35-0.44	Equivocal	Inconclusive results. Repeat collection if clinically indicated.
< 0.35	Negative	E. histolytica antibodies NOT detected. False negative results may occur in the first 2 weeks of symptom onset. Repeat collection if clinically indicated.

Interpretation

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Positive results are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition

Specimens that are positive for Amoebiasis serology are reported to the Medical Officer of Health as per the Health Protection and Promotion Act.

References

Cooney J, Siakavellas SI, Chiodini PL, et al. Recent advances in the diagnosis and management of amoebiasis. Frontline Gastroenterology 2025;16:37-50.