A Giardia antigen stool test is a laboratory assay that detects Giardia intestinalis proteins (antigens) in a stool sample to diagnose giardiasis. It is more sensitive and faster than microscopy, often requiring a single specimen, and helps confirm infection in people with persistent diarrhea, abdominal cramps or weight loss. Results usually return within hours to a few days and guide treatment decisions.

Giardia antigens include variant-specific surface proteins (VSPs) covering trophozoite surfaces, structural giardins (e.g., α‑giardin) in the cytoskeleton, and cyst wall proteins (CWP1–CWP3) produced during encystation. These surface and secreted proteins are principal targets of host immunity and form the basis for stool antigen diagnostic tests; other metabolic and cytosolic proteins may also be antigenic.

During pregnancy, giardiasis is usually managed with paromomycin—an oral, poorly absorbed antibiotic considered safer for the fetus—especially in the first trimester. Metronidazole or tinidazole may be considered later or if paromomycin is ineffective. Confirm infection with stool testing and follow your obstetrician’s guidance on drug choice, dose and duration. Also use rehydration and strict hygiene to prevent spread.

Giardia stool antigen is usually positive during active infection and often becomes negative within 2–4 weeks after effective treatment. Antigen can persist for several weeks despite symptom improvement, so an early post-treatment positive result doesn't always indicate failure. For confirmation or if symptoms continue, clinicians typically repeat testing about 2–4 weeks after completing therapy.

Giardia positive means a lab test found Giardia intestinalis, a microscopic intestinal parasite that causes giardiasis. It often causes watery or greasy diarrhea, abdominal cramps, bloating, gas and weight loss. The infection spreads via contaminated water, food, or person-to-person contact. Prescribed antiparasitic drugs (for example metronidazole, tinidazole, or nitazoxanide) plus fluids usually clear it.

Giardia is best treated with antiprotozoal medications rather than typical antibiotics. First-line options are nitroimidazoles — tinidazole (single-dose, high cure rates) or metronidazole (multi-day course). Nitazoxanide is an alternative, and albendazole may be used alone or with a nitroimidazole in some cases. Consult a healthcare provider for diagnosis, exact dosing, and safety considerations.