VHOSPITAL.CLINIC · Immunological Test
The stool antigen test is the recommended first-line diagnostic test for giardiasis — detecting Giardia-specific antigens (GSA65 or GLST) with 94–99% sensitivity and results within hours.
An immunochromatographic or ELISA test that detects parasite-specific antigens directly in stool — high sensitivity with same-day results.
ELISA or immunochromatographic (rapid) antigen tests detect Giardia lamblia cyst wall protein or heat-stable antigen in stool. They outperform stool microscopy in sensitivity and are far easier to standardise.
A fresh or preserved stool sample is tested with the antigen cassette (rapid) or processed in the laboratory (ELISA). Results in 5–30 minutes for rapid tests; 1–4 hours for ELISA. No special staining required. Single stool sample is sufficient for antigen testing.
Positive antigen test: confirms Giardia infection — initiate treatment. Negative antigen test with strong clinical suspicion: repeat test (low sensitivity in early infection) or add stool microscopy. Antigen test does not differentiate between Giardia assemblages (A vs B).
Sensitivity: 94–99% (ELISA); 85–94% (rapid immunochromatographic). Specificity: 97–100%. Significantly more sensitive than single-sample stool microscopy (50–70%). Three stool samples over 3 days approach the sensitivity of a single antigen test.
Yes. A single stool antigen test (ELISA or rapid) detects Giardia with 94–99% sensitivity — significantly better than single stool microscopy (50–70%). For maximal microscopy sensitivity, three stool samples over 3 days are needed, which is impractical for patients.
Collect stool in a clean, dry container — no toilet water contamination. Fresh stool should be tested within 2 hours or refrigerated. For preserved samples, use a sodium acetate-acetic acid-formalin (SAF) or formalin-ethyl acetate preservative. A single random stool sample is sufficient.
Yes. A negative antigen test 2–4 weeks after completing treatment confirms parasitological cure. However, antigen may persist for 2–3 weeks post-treatment even after cure — so waiting the full 2 weeks before retesting is important.
Giardiasis is a common intestinal infection caused by the protozoan parasite Giardia lamblia, transmitted through contaminated water or food. It presents with chronic diarrhoea, bloating, and malabsorption, and is treated with metronidazole or tinidazole.
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