VHOSPITAL.CLINIC · Diagnostic 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.
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.
Stool Antigen Test helps confirm Giardiasis, which can cause these symptoms:
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