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Entamoeba histolytica IgG Antibody (Amoebiasis) - Serum
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Antibody test for amoebiasis.
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Entamoeba histolytica IgG Antibody (Amoebiasis) - Serum
- Why is it done?
- Test Description: This test detects IgG antibodies against Entamoeba histolytica in serum, indicating current or past infection with the parasitic protozoan that causes amoebiasis (amoebic dysentery and liver abscess).
- Primary Indications: Suspicion of amoebiasis in patients with prolonged diarrhea, dysentery, or abdominal pain; evaluation of unexplained fever and hepatomegaly; diagnosis of amoebic liver abscess; screening in endemic areas; travel history to endemic regions with gastrointestinal or hepatic symptoms.
- Typical Timing: When patients present with acute or chronic gastrointestinal symptoms consistent with parasitic infection; when fever and right upper quadrant tenderness suggest hepatic involvement; following exposure in endemic regions; during epidemiological investigations of outbreaks.
- Normal Range
- Normal Result (Negative): Absence of detectable IgG antibodies (typically reported as <1.0 or negative); indicates no current or past infection with Entamoeba histolytica.
- Abnormal Result (Positive): Detectable IgG antibodies at any titer (≥1.0 or positive); indicates past or current infection with E. histolytica.
- Units of Measurement: Titer (expressed as reciprocal dilution: 1:128, 1:256, etc.) or qualitative (positive/negative); some labs use semiquantitative scoring (1+, 2+, 3+, 4+).
- Clinical Interpretation: Negative results effectively exclude amoebic liver abscess and invasive amoebiasis; positive results indicate immune response to E. histolytica (either current or past infection); higher titers are more consistent with active invasive disease; serology is less reliable in acute intestinal disease and asymptomatic colonization.
- Interpretation
- Positive IgG Antibody: Indicates past or current E. histolytica infection; in context of amoebic liver abscess, sensitivity reaches 90-100%; in intestinal amoebiasis, sensitivity is lower (60-80%); highly specific (>95%) for invasive disease; antibodies typically persist for years after treatment, limiting ability to distinguish current from past infection.
- Negative IgG Antibody: Effectively excludes amoebic liver abscess (>99% negative predictive value); does not rule out acute dysentery or asymptomatic intestinal colonization; may be negative in immunocompromised patients or very early infection before antibody formation.
- Titer Significance: Higher titers (1:512 or greater) suggest active invasive disease; lower titers (1:128-1:256) may indicate past infection or early disease; titer levels do not correlate reliably with disease severity or treatment response; serial titers are not recommended for clinical monitoring.
- Factors Affecting Results: Immunosuppression may produce false negatives; cross-reactivity with other protozoan parasites possible but minimal; prior E. dispar or E. moshkovskii infection unlikely to cause false positives; timing of antibody appearance (typically 1-2 weeks after invasive disease onset); persistence of antibodies years post-treatment; geographic and endemic area considerations.
- Clinical Significance: Excellent test for diagnosing invasive amoebiasis and hepatic abscess; limited utility in diagnosing acute dysentery; should be combined with stool microscopy for intestinal disease; imaging (ultrasound/CT) often performed concurrently when liver abscess suspected; serological positivity supports need for antiamebic therapy.
- Associated Organs
- Primary Organ Systems: Gastrointestinal tract (colon and cecum as primary sites); liver (most common extraintestinal site); potentially lungs, brain, and other organs in disseminated disease.
- Common Associated Conditions: Amoebic dysentery (acute and chronic); amoebic liver abscess (pyogenic, most common extraintestinal manifestation); amoebic colitis; toxic megacolon; intestinal perforation; peritonitis; extraintestinal ameobiasis including lung abscess, pleural effusion, and brain abscess.
- Diseases This Test Helps Diagnose: Amoebiasis (infection with E. histolytica); amoebic liver abscess; invasive intestinal amoebiasis; amoebic colitis; disseminated amoebic disease affecting lungs, brain, or other organs; post-treatment complications.
- Potential Complications Associated with Abnormal Results: Liver abscess rupture into peritoneal or pleural cavity; sepsis; secondary bacterial infection of amoebic abscess; intestinal perforation with peritonitis; toxic megacolon; chronic intestinal strictures; pulmonary involvement with respiratory compromise; brain involvement causing neurological complications; fulminant colitis in severe cases; hemodynamic instability and shock in disseminated disease.
- Follow-up Tests
- Confirmatory and Diagnostic Tests: Stool microscopy (multiple samples recommended to detect trophozoites or cysts); stool antigen detection or PCR; colonoscopy with biopsy for intestinal disease diagnosis; abdominal ultrasound or CT scan to evaluate for liver abscess.
- Imaging and Assessment: Hepatic ultrasound if liver involvement suspected; abdominal CT for detailed anatomy and complications; chest imaging if pulmonary involvement suspected; cranial imaging if neurological symptoms present.
- Laboratory Monitoring: Complete blood count; liver function tests (AST, ALT, alkaline phosphatase, bilirubin); blood culture if secondary infection suspected; assessment of renal function and electrolytes in severe disease.
- Treatment Monitoring: Repeat imaging to assess abscess resolution (ultrasound/CT); stool studies post-treatment to confirm eradication; clinical assessment of symptom resolution; repeat serology not recommended for treatment monitoring.
- Related Complementary Tests: Entamoeba histolytica IgM antibody (indicates acute infection); E. dispar serology (to differentiate from E. histolytica); other parasitic serology if co-infections suspected; inflammatory markers (CRP, ESR) to assess disease activity.
- Monitoring Frequency: Initial diagnosis followed by baseline investigations; imaging repeated at 2-4 weeks into treatment for liver abscess; clinical follow-up at treatment completion; stool studies at end of therapy; no routine serial serology needed post-treatment.
- Fasting Required?
- Fasting Requirement: NO - Fasting is not required for this test.
- Sample Collection: A simple serum blood draw is all that is required; can be collected at any time of day; no dietary restrictions necessary.
- Medications: No medications need to be avoided or withheld before this test; continue all regular medications as prescribed.
- Other Preparation Requirements: No special preparation needed; patient should remain calm during blood draw; arm should be in relaxed state for venipuncture; inform phlebotomist of any bleeding disorders or difficulty with blood draws; maintain normal fluid intake and hydration.
- Specimen Handling: Blood is collected in a sterile tube without anticoagulant; serum is separated and may be refrigerated if not processed immediately; specimen should be sent to laboratory promptly; stable for several days when refrigerated.
How our test process works!
