Typhi Dot IgM

Bacterial/ Viral

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No Fasting Required

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

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Typhi Dot IgM Test Information Guide

Why is it done?
- Detects IgM antibodies against Salmonella typhi, the causative agent of typhoid fever
- Primary indication: Diagnosis of acute or early-stage typhoid fever infection
- Recommended when patients present with prolonged fever, headache, muscle aches, and abdominal discomfort
- Useful for rapid serological diagnosis in endemic areas and in patients with recent travel history to typhoid-prone regions
- Typically performed during the first 1-2 weeks of illness when IgM antibodies first appear
- Can be used as an adjunct to blood culture for faster confirmation of typhoid diagnosis
Normal Range
- Negative/Non-Reactive: Optical Density (OD) value less than the cutoff (typically < 0.04-0.08 depending on the assay kit)
- Positive/Reactive: OD value greater than or equal to the cutoff threshold
- Borderline/Equivocal: OD values within a gray zone that may require repeat testing or additional confirmation
- Unit of measurement: Optical Density (OD) ratio or arbitrary units specific to the dot ELISA platform
- Normal/Negative result indicates absence of IgM antibodies against S. typhi, suggesting no acute or recent typhoid infection
- Abnormal/Positive result indicates presence of IgM antibodies, suggesting acute or recent S. typhi infection
Interpretation
- Positive IgM Result: Indicates acute or recent typhoid fever infection; patient likely infected within 1-3 months; considered highly suggestive of active typhoid disease, especially if combined with clinical symptoms and positive blood culture
- Negative IgM Result: Suggests absence of acute typhoid infection; however, early in infection (first 3-5 days) IgM may still be negative; chronic carriers may not have detectable IgM; repeat testing may be warranted if clinical suspicion remains high
- Equivocal/Borderline Result: Suggests uncertain or inconclusive finding; warrants repeat testing after 5-7 days; should be correlated with clinical presentation and other diagnostic findings
- Factors affecting interpretation:
- Timing of test during illness: Early detection rates increase with duration of fever (lower sensitivity in first 3-5 days)
- Prior typhoid vaccination may affect interpretation; vaccinated individuals may have persistent antibodies
- Cross-reactivity with other salmonella species may occur in endemic areas
- Immunocompromised patients may show delayed or absent antibody responses
- Clinical significance: IgM antibodies typically persist for 3-6 months; presence after this period suggests new infection or chronic carrier state
Associated Organs
- Primary organ systems involved:
- Gastrointestinal tract (initial infection site and colonization)
- Immune system (lymphoid tissues and Peyer's patches)
- Reticuloendothelial system (liver, spleen, bone marrow)
- Biliary system (gallbladder as chronic carrier site)
- Medical conditions commonly associated with abnormal results:
- Acute typhoid fever (Salmonella typhi bacteremia)
- Paratyphoid fever (caused by related Salmonella species)
- Chronic carrier state of typhoid
- Enteric fever with complications (intestinal perforation, myocarditis, encephalopathy)
- Potential complications of abnormal results (indicating active infection):
- Intestinal perforation and peritonitis if untreated
- Septic shock and multi-organ failure
- Hepatic dysfunction and cholecystitis
- Neurological complications including typhoid encephalopathy
- Myocarditis and hemodynamic instability
Follow-up Tests
- If positive result:
- Blood culture (gold standard for confirmation; higher sensitivity if drawn early in illness)
- Typhi Dot IgG (to assess immune response stage and differentiate acute vs. chronic/past infection)
- Complete blood count (CBC) to assess severity of infection and complications
- Liver function tests (AST, ALT, bilirubin) to evaluate hepatic involvement
- Renal function tests (creatinine, BUN) for renal involvement assessment
- Blood glucose monitoring (typhoid can cause hypoglycemia)
- Stool culture (once infection confirmed, for chronic carrier detection)
- Urine culture (to rule out urinary tract involvement)
- If negative result with high clinical suspicion:
- Repeat IgM testing after 5-7 days (due to early false-negative rates)
- Blood culture for direct organism detection
- Bone marrow culture (higher sensitivity than blood culture, especially in later stages)
- Widal test (O and H agglutinins) as supplementary diagnostic tool
- Monitoring recommendations:
- Clinical response to antibiotic therapy (defervescence typically within 3-5 days of appropriate treatment)
- Repeat cultures at end of antibiotic course to confirm microbiological cure
- Long-term stool cultures for chronic carrier detection (especially in women and elderly)
Fasting Required?
- Fasting requirement: No - fasting is NOT required for this serological test
- Sample collection instructions:
- 5-10 mL of venous blood is collected in a serum separator tube (SST) or plain tube
- No anticoagulants should be used; serum is preferred for serological testing
- Allow sample to clot at room temperature for 30 minutes, then centrifuge to obtain clear serum
- Timing considerations:
- Test can be performed at any time of day without timing restrictions
- Ideally performed during acute phase of illness (first 1-3 weeks) when IgM antibodies are most likely to be present
- Medications to avoid:
- No specific medications need to be withheld prior to serum collection
- However, starting antibiotic therapy may reduce positivity if IgM is still developing; ideally test before or early in antibiotic treatment
- Other patient preparation requirements:
- Patient should be in stable condition for blood collection (sitting or lying down preferred)
- Rest for 5 minutes before collection is recommended to avoid hemoconcentration
- No specific diet restrictions apply; normal diet is acceptable
- Serum samples should be stored at 2-8°C if not tested immediately; stable for 5-7 days at refrigerated temperature

How our test process works!