Giardia Antigen Detection

Bacterial/ Viral

Report in 48Hrs

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No Fasting Required

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Stool antigen test for Giardia.

₹1,717₹2,453

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Giardia Antigen Detection - Comprehensive Medical Test Guide

Why is it done?
- Test Purpose: Detects Giardia lamblia (also known as Giardia intestinalis or Giardia duodenalis) antigens in stool samples to identify giardiasis, a parasitic infection of the small intestine.
- Primary Indications: Persistent diarrhea lasting more than a few days, chronic loose or fatty stools, malabsorption symptoms, abdominal cramping and bloating, weight loss, nausea, and suspected exposure to contaminated water or food.
- Typical Timing: Performed when patients present with acute or chronic gastrointestinal symptoms, following travel to endemic areas, after outbreaks of waterborne illness, or during investigation of pediatric failure to thrive associated with diarrhea. Can be used for initial diagnosis or to confirm cure after treatment.
- Special Populations: Immunocompromised individuals, travelers to developing countries, hikers/campers exposed to untreated water, and individuals with exposure to contaminated food sources.
Normal Range
- Normal Result (Negative): No Giardia antigen detected in the stool sample; indicates absence of Giardia lamblia infection.
- Abnormal Result (Positive): Giardia antigen detected in stool sample; confirms active Giardia lamblia infection. Most tests report results as either Positive or Negative (qualitative testing).
- Units of Measurement: Qualitative result (Positive/Negative) or semi-quantitative results reported as Negative, Weak Positive, or Strong Positive depending on laboratory methodology (ELISA, immunochromatography, or PCR-based assays).
- Reference Range: Negative (no antigen present). A negative result does not completely rule out infection, particularly if clinical suspicion is high or symptoms persist. A positive result confirms active infection requiring treatment.
- Test Sensitivity and Specificity: Antigen detection tests typically have 90-95% sensitivity and 99% specificity. Sensitivity may be lower with light infections or when sampling single specimens. Multiple samples increase diagnostic accuracy.
Interpretation
- Positive Result: Confirms Giardia lamblia infection (giardiasis). Patient has active parasitic infection with cysts or trophozoites shedding antigens in stool. Indicates need for treatment with antiparasitic agents (typically metronidazole, tinidazole, or nitazoxanide). Symptomatic patients should receive therapy; asymptomatic carriers may be treated depending on clinical circumstances and infection duration.
- Negative Result: No Giardia antigen detected; suggests absence of current infection. However, negative results do not definitively exclude infection, particularly in early stages or with low parasite burden. If clinical suspicion remains high with persistent symptoms, repeat testing at 3-7 day intervals or stool microscopy is recommended. Up to 3 serial specimens may be needed for optimal sensitivity.
- Weak Positive/Borderline Results: May indicate light infections or early stages of disease. Recommend repeating testing if clinical symptoms persist. Weak positives are generally treated as positive and warrant consideration for therapy, especially in symptomatic patients.
- Factors Affecting Results: Intermittent antigen shedding may produce false negatives; timing of infection relative to testing matters; recent antiparasitic therapy; barium studies or bismuth compounds may interfere with detection; immunosuppression may affect antigen levels; specimen quality and handling; sample volume adequacy.
- Clinical Significance: Positive result in symptomatic patients strongly supports diagnosis of giardiasis. In asymptomatic individuals, may represent colonization or recent infection. Results should be correlated with clinical presentation, symptom duration, epidemiologic exposure history, and response to empiric therapy. Test is superior to microscopy for diagnosis due to higher sensitivity and specificity.
- Post-Treatment Monitoring: Test can be repeated 2-3 weeks after completing antiparasitic therapy to confirm cure. Continued positive results after adequate treatment may indicate treatment failure, reinfection, or non-compliance. Some patients may have persistent positivity despite clinical improvement.
Associated Organs
- Primary Organ System: Gastrointestinal tract, specifically the small intestine (duodenum and jejunum), where Giardia trophozoites attach to the intestinal epithelium and cause inflammation and malabsorption.
- Diseases Diagnosed/Monitored: Giardiasis (Giardia lamblia infection), including acute giardiasis presenting with watery diarrhea, chronic giardiasis with persistent diarrhea, and asymptomatic giardiasis in carriers. Associated with traveler's diarrhea, especially from waterborne exposure.
- Clinical Manifestations: Acute symptoms include sudden onset diarrhea, abdominal cramps, bloating, flatulence, and nausea. Chronic symptoms include persistent loose/fatty stools, malabsorption, vitamin deficiencies (especially fat-soluble vitamins A, D, E, K and B12), weight loss, and failure to thrive in children. Lactose intolerance may develop temporarily.
- Potential Complications: Severe dehydration and electrolyte imbalances from prolonged diarrhea, protein-energy malnutrition, iron deficiency anemia, vitamin B12 and folic acid deficiency, growth retardation in children, reactive arthritis, and chronic complications affecting quality of life if untreated.
- Associated Conditions: Common in patients with HIV/AIDS (particularly CD4 < 200), immunoglobulin A deficiency, other immunocompromised states, and may be associated with other parasitic infections or bacterial overgrowth secondary to malabsorption.
- Risk Factors: Ingestion of contaminated water (inadequately treated water supplies), consumption of contaminated food, person-to-person transmission in day care settings, exposure during outdoor recreation and camping, travel to endemic areas with poor sanitation, and sexual contact practices among high-risk groups.
Follow-up Tests
- Confirmatory Testing: Stool microscopy for Giardia cysts/trophozoites if antigen testing is negative but high clinical suspicion persists. Stool PCR testing offers superior sensitivity and specificity. Duodenal biopsy or aspirate with histology may be performed in cases where diagnosis remains uncertain after stool testing.
- Nutritional Status Assessment: Complete metabolic panel to assess for hypokalemia, hyponatremia, and dehydration; complete blood count for anemia and lymphocyte assessment; vitamin B12 and folate levels for deficiency; albumin and prealbumin for protein status; assessment of vitamin A, D, and fat-soluble vitamin deficiencies.
- Assessment of Complications: Urinalysis and serum osmolality for dehydration assessment; iron studies if anemia is present; prothrombin time if vitamin K deficiency suspected; assessment for reactive arthritis if joint symptoms develop.
- Screening Tests: Comprehensive stool analysis including culture and ova/parasites; testing for other parasites (cryptosporidium, entamoeba) if appropriate; bacterial culture if bacterial infection suspected.
- Post-Treatment Monitoring: Repeat Giardia antigen testing 2-3 weeks after completing therapy to confirm cure; repeat testing if symptoms persist after treatment; testing may be performed at 1-3 month intervals to document sustained cure in immunocompromised patients.
- Testing in High-Risk Groups: Repeat testing may be recommended for day care workers and contacts, immunocompromised individuals at risk, and travelers to endemic areas; baseline testing in some clinical situations.
- Immunological Studies: CD4 count in HIV-positive patients; immunoglobulin levels if immunodeficiency suspected; other immunological assessments based on clinical presentation.
- Imaging Studies: Rarely performed; abdominal imaging only if complications suspected or diagnosis remains unclear; endoscopy with duodenal biopsy in persistent cases.
Fasting Required?
- Fasting Requirement: NO - Fasting is NOT required for Giardia antigen detection testing.
- Specimen Collection Requirements: Fresh stool sample is preferred; specimen should be collected in a clean, leak-proof container; approximately 8-10 grams of stool or the volume specified by the laboratory; sample should be at room temperature and processed within 1-2 hours for optimal results; refrigerated samples may be stored up to 24 hours if immediate processing is not possible.
- Pre-Test Instructions: No dietary restrictions necessary; patient may eat and drink normally; no special bowel preparation required; natural bowel movements preferred for collection; avoid contaminating stool specimen with urine; collect sample on a natural bowel movement, not from toilet water.
- Medications to Avoid: Avoid bismuth compounds (bismuth subsalicylate/Pepto-Bismol) for 2 weeks before testing as they may interfere with test results; avoid recent antiparasitic medications unless specifically instructed; avoid antimotility agents (loperamide) unless prescribed; barium studies should not be performed within 2 weeks before testing as barium may interfere with detection.
- Special Considerations: Multiple specimens (3 samples collected on separate days) may be recommended for optimal sensitivity if initial results are negative with persistent symptoms; inform laboratory if patient has received recent antiparasitic therapy; label specimens clearly with date, time, and patient identification; follow specific laboratory instructions for specimen collection and transport.
- Contraindications or Precautions: None specific to patient fasting or medication use. However, inform provider of recent travel history, water exposure, potential contamination sources, and symptom timeline to improve diagnostic interpretation.

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