Typhi Dot IgG & IgM

Bacterial/ Viral

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No Fasting Required

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

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Typhi Dot IgG & IgM - Comprehensive Test Information Guide

Why is it done?
- Detection of Salmonella typhi infection: This test detects specific antibodies (IgG and IgM) against Salmonella typhi, the bacterium that causes typhoid fever
- Diagnosis of acute typhoid fever: IgM antibodies indicate recent or active infection, making this useful for diagnosing acute disease
- Identification of chronic carriers: IgG antibodies suggest past infection or chronic carrier status, important for epidemiological tracking
- Assessment of vaccination response: Helps determine if typhoid vaccination has induced adequate antibody response
- Typical indications: Fever of unknown origin in endemic areas, travel history to typhoid-endemic regions, suspected enteric fever, fever with rose spots and abdominal symptoms, or prophylactic screening in high-risk populations
Normal Range
- IgG Typhi: Negative or < 0.90 S/CO (Signal-to-Cutoff ratio) - Normal range indicates no current infection or past exposure
- IgM Typhi: Negative or < 0.90 S/CO - Normal range indicates no acute or recent infection
- Interpretation scale: - Negative: < 0.90 S/CO (No antibodies detected) - Borderline/Equivocal: 0.90 - 1.10 S/CO (Repeat testing recommended) - Positive: > 1.10 S/CO (Antibodies detected)
- Normal result: Bilateral negative results for both IgG and IgM indicate no evidence of Salmonella typhi infection or recent vaccination
- Abnormal result: Any positive value suggests exposure to or infection with Salmonella typhi requiring clinical correlation
Interpretation
- IgM Positive + IgG Negative: Suggests acute or recent typhoid infection (within 1-2 weeks); indicates active disease requiring treatment
- IgM Positive + IgG Positive: Indicates convalescent phase or recent infection; patient may be in recovery stage or early chronic carrier state
- IgM Negative + IgG Positive: Suggests past infection, immunity from previous disease, chronic carrier status, or response to typhoid vaccination; no acute infection
- IgM Negative + IgG Negative: No evidence of typhoid infection or vaccination; rules out typhoid as cause of fever
- Factors affecting interpretation: - Timing of serology: Antibodies may not be detectable in first 3-5 days of illness - Cross-reactivity: Other Salmonella species may cause false positives - Vaccination status: Recent typhoid vaccination produces positive IgG - Geographic origin: Endemic area prevalence affects positive predictive value - Previous infections: Past exposure may complicate interpretation
- Clinical significance of borderline values: Borderline (equivocal) results require repeat testing after 7-10 days; serial sampling showing four-fold rise is highly significant for acute infection
Associated Organs
- Gastrointestinal system: Primary site of Salmonella typhi multiplication; causes inflammation of the intestinal mucosa, Peyer's patches, and mesenteric lymph nodes
- Hepatic system: Liver involvement results in hepatomegaly and hepatitis; pathogenic organisms invade hepatocytes causing inflammation
- Lymphoid tissue: Splenomegaly occurs due to reticuloendothelial system activation and bacterial proliferation
- Central nervous system: Can develop typhoid encephalopathy, meningitis, or neuropsychiatric manifestations in severe cases
- Bone marrow: Salmonella typhi can seed bone marrow causing bacteremia and systemic infection
- Associated diseases and conditions: - Typhoid fever (enteric fever): Systemic infection characterized by prolonged fever, abdominal pain, and rose spots - Chronic carrier state: 1-5% of patients develop chronic carriage with persistent bile duct colonization - Intestinal perforation: Serious complication in untreated cases leading to peritonitis - Myocarditis: Cardiac involvement causing dysrhythmias - Pneumonia and respiratory complications - Septic shock in severe disease - Focal infections: Abscess formation in various organs
- Potential complications: Mortality rate of 10-30% in untreated cases; permanent neurological sequelae in some patients; chronic gallbladder disease; secondary infections
Follow-up Tests
- Blood culture: Gold standard for typhoid diagnosis; should be performed early in disease course before antibiotics; often positive in first 1-2 weeks
- Stool culture: Positive in later stages of disease and in chronic carriers; helps identify chronic carrier state for public health management
- Urine culture: May be positive in some cases; alternative specimen if blood/stool unavailable
- Bone marrow culture: Most sensitive test (80-90% positive); reserved for cases where blood culture is negative but typhoid strongly suspected
- Widal test: Traditional serological test measuring O and H antibodies; less specific than Typhi Dot but may be ordered for comparison; subject to false positives
- Complete blood count: Assess for leukopenia or leukocytosis; evaluate for anemia and thrombocytopenia
- Liver function tests: Evaluate hepatomegaly and hepatitis; important in severe disease
- Repeat serology: IgG and IgM testing after 7-10 days if initial results are borderline or equivocal; four-fold rise in titer is diagnostic for acute infection
- Molecular testing (PCR): Emerging alternative with improved sensitivity and specificity; detects bacterial DNA in blood samples
- Imaging studies: Abdominal ultrasound or CT scan if complications suspected (perforation, abscess); assess for splenomegaly and hepatomegaly
- Monitoring frequency: For acute cases, repeat serological testing 1-2 weeks after initial test; for chronic carriers, periodic surveillance depends on occupational exposure and public health recommendations
Fasting Required?
- Fasting requirement: NO - Fasting is not required for Typhi Dot IgG & IgM testing
- Blood specimen collection: Can be performed at any time of day; food and beverage intake do not affect antibody detection
- Sample requirements: 3-5 mL of serum or plasma collected in standard collection tube; proper labeling and handling essential for accurate results
- Medication restrictions: No specific medications need to be discontinued; however, inform healthcare provider of any recent antibiotics as they may reduce bacterial load and affect blood culture results if concurrent testing is planned
- Special preparations: No special patient preparation required; patient can continue normal activities before testing; hydration status does not affect antibody detection
- Specimen stability: Serum samples stable at room temperature for 24 hours; store at 2-8°C if testing delayed; do not freeze unless long-term storage required
- Timing considerations: Optimal timing for testing is 1-2 weeks after symptom onset for maximum antibody detection; earlier testing may result in false negatives

How our test process works!