Typhi Dot IgG

Bacterial/ Viral

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No Fasting Required

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Detects IgG antibodies against Salmonella Typhi, the bacterium responsible for typhoid fever

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Typhi Dot IgG Test Information Guide

Why is it done?
- Detects IgG antibodies against Salmonella typhi, the bacterium responsible for typhoid fever
- Diagnoses typhoid fever in patients presenting with fever, headache, abdominal pain, and rose spots rash
- Identifies individuals with past typhoid infection or immunization
- Used in endemic areas or for travelers returning from typhoid-prone regions
- Typically performed during later stages of illness (second to third week onwards) when IgG antibodies are more prevalent
- Useful for confirming diagnosis when blood culture results are negative or unavailable
Normal Range
- Negative Result: < 0.9 Index or Absent/Not Detected (depending on laboratory method used)
- Positive Result: > 1.0 Index or Present/Detected
- Borderline/Equivocal: 0.9 - 1.0 Index (requires retesting or clinical correlation)
- Units of Measurement: Index value (optical density ratio) or qualitative (Positive/Negative/Equivocal)
- Normal (Negative) indicates: Absence of IgG antibodies to S. typhi, suggesting no previous infection or recent vaccination
- Abnormal (Positive) indicates: Presence of IgG antibodies suggesting past or current typhoid infection, or previous immunization
Interpretation
- Positive IgG Result (Index > 1.0): Indicates past infection with S. typhi or previous typhoid vaccination. IgG appears 1-2 weeks after symptom onset and persists for years. May indicate chronic carrier state if accompanied by positive blood culture or stool culture.
- Negative IgG Result (Index < 0.9): Suggests no previous typhoid infection or very early stage illness (first week). Cannot exclude active infection if taken during acute phase when IgM is predominant.
- Rising Titers (Serial Testing): Fourfold or greater increase between acute and convalescent sera collected 10-14 days apart is more significant for active infection than single positive result.
- Combined with IgM Results: IgG+ IgM+ suggests acute or recent infection; IgG+ IgM- suggests past infection or chronic carriage; both negative suggests no infection.
- Factors Affecting Results: Previous typhoid vaccination (Ty21a oral or polysaccharide vaccine) may produce positive results; timing of blood draw relative to symptom onset; immunocompromised status may affect antibody production; cross-reactivity with other Salmonella species may occur.
- Clinical Significance: IgG positivity alone is not diagnostic of acute typhoid and must be correlated with clinical presentation, epidemiology, and other diagnostic tests (blood culture, stool culture, Widal test). Best used as confirmatory test rather than sole diagnostic tool.
Associated Organs
- Primary Organ Systems Involved: Gastrointestinal tract (primary infection site), Lymphoid tissue (mesenteric lymph nodes, Peyer's patches), Liver and spleen (hepatosplenomegaly common), Blood/Vascular system (bacteremia), Central nervous system (in severe cases).
- Associated Conditions/Diseases: Typhoid fever (enteric fever), Chronic typhoid carriage (biliary tract colonization), Typhoid-related sepsis, Typhoid myocarditis, Typhoid meningitis, Guillain-Barré syndrome (post-typhoid complication).
- Complications Associated with Abnormal Results: Intestinal perforation (20-40% mortality if untreated), Toxic encephalopathy/delirium, Hypovolemic shock from diarrhea, Acute kidney injury, Myocarditis and heart failure, Secondary bacterial peritonitis, Relapse typhoid, Death if untreated (20-30% mortality rate).
- Long-term Effects: Chronic carrier state (1-5% of infected individuals), IgG persistence for years despite treatment, Potential for spreading infection to others through fecal-oral route.
Follow-up Tests
- Confirmatory Testing: Blood culture (gold standard for diagnosis during first week), Stool culture (positive after 1-4 weeks, identifies carriage), Bone marrow culture (highest sensitivity if other cultures negative), Urine culture (less sensitive but possible).
- Complementary Serological Tests: Typhi Dot IgM (for acute phase detection), Widal test (O antigen and H antigen titers), ELISA for S. typhi specific IgG and IgM, Rapid diagnostic tests for S. typhi antigen.
- Monitoring Tests if Positive: Repeat serology 2-3 weeks later (rising titers confirm acute infection), Repeat stool culture at completion of treatment to verify eradication, Follow-up testing for chronic carriers.
- General Investigation Tests: Complete blood count (leukopenia, relative lymphocytosis), Liver function tests (elevated transaminases), Renal function tests (assess for kidney injury), Blood glucose (hypoglycemia possible), Imaging: CT abdomen (assess for perforation or complications).
- Monitoring Frequency: During acute illness: Monitor daily during hospitalization; Convalescence: Follow-up serology at 2-3 weeks if diagnosis uncertain; Chronic carriers: Annual monitoring with stool cultures; Contacts: Screen contacts with serology and cultures.
- Related Diagnostic Tests: Molecular testing (PCR for S. typhi DNA), Antimicrobial susceptibility testing on isolated organisms, Hepatitis serology (to exclude other causes of illness), Blood smear examination.
Fasting Required?
- Fasting Requirement: No
- Fasting is not required for the Typhi Dot IgG test as it is a serum-based antibody detection test that measures immune response and is not affected by food or fluid intake.
- Patient Preparation Requirements: Eat and drink normally before the test; No special dietary restrictions; Patient can take regular medications unless specifically instructed otherwise by physician.
- Sample Collection: Serum sample (typically 3-5 mL) collected via venipuncture into SST (Serum Separator Tube) or plain blood collection tube; Can be collected at any time of day; No special timing considerations.
- Medications: No medications need to be withheld specifically for this test; Continue all prescribed medications; Inform laboratory of any recent vaccinations (may affect interpretation); Current antibiotics do not interfere with test results.
- Timing Recommendations: Ideally performed after 1-2 weeks of illness onset (when IgG antibodies are present); For serial testing, collect second sample 10-14 days after first sample; Can be performed any day of the week.
- Special Instructions: Inform phlebotomist of fever or acute illness; Patient should remain calm to minimize stress-related effects; Allow serum to clot if using SST tube before transport; Sample should reach laboratory within 24 hours or be refrigerated.

How our test process works!