What this test measures
Lateral-flow or ELISA-based IgM antibody assay against the 50-kDa outer membrane protein of S. Typhi. IgM rises in the second week of illness. Sensitivity and specificity reports vary widely (50-90% sensitivity, 70-95% specificity). Better than Widal in early disease but not equivalent to blood culture (the gold standard).
Why it matters
Typhoid is endemic in India (estimated 4.5 million cases annually) with rising drug resistance — XDR strains are emerging in Pakistan and parts of India. Rapid diagnostics are important for outbreak response and primary care, but no single rapid test has the sensitivity / specificity of blood culture. Typhidot is widely used in India because of speed and cost, but should not replace blood culture where available. Treatment is increasingly with ceftriaxone or azithromycin given resistance concerns.
How to prepare
No fasting required. Sample 5–10 days after fever onset for best sensitivity (IgM rises in second week). Disclose any recent vaccination (typhoid vaccine — Vi capsular polysaccharide doesn't cross-react with 50-kDa OMP test but oral Ty21a vaccine may), recent antibiotic use, prior typhoid history.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Typhidot IgM (reactive / non-reactive)[1][2] | Non-reactive | Non-reactive — typhoid less likely. Window-period false negatives common in first week. Order blood culture and clinical evaluation. | Reactive — supports typhoid diagnosis in suggestive clinical context (prolonged fever, headache, abdominal pain, relative bradycardia, hepatosplenomegaly, rose spots). Confirm with blood culture where possible. Start empirical antibiotic (ceftriaxone or azithromycin) per local resistance pattern. |
Typhoid diagnostic tests
| Test | Sensitivity | Specificity | Best window |
|---|---|---|---|
| Blood culture (gold standard) | 60-80% | ~100% | Week 1-2 |
| Bone marrow culture | 90% | ~100% | Any week |
| Stool culture | 30-50% | Specific | Week 3-4 |
| Typhidot IgM | 50-90% | 70-95% | Week 2 |
| Widal test | Poor | Poor (high false positives in India) | Limited utility |
Frequently asked questions
Is Typhidot better than Widal?
Generally yes for early disease — Widal has very poor specificity in endemic India (baseline anti-O / anti-H titres are high in normal population from past exposure / vaccination). Typhidot has better specificity but still inferior to blood culture.
Should I get blood culture too?
Yes if possible — blood culture is the gold standard, confirms diagnosis definitively, and provides antibiotic sensitivity (essential given rising drug resistance).
How long after fever onset should I test?
Days 5-10 of fever for best IgM yield. Earlier testing (days 1-4) may be negative; later testing (after week 2) may overlap with recovery IgG.
Does typhoid vaccine affect this test?
Vi capsular polysaccharide vaccine doesn't cross-react with the 50-kDa OMP target. Oral Ty21a vaccine may produce some background reactivity. Disclose vaccination history.
What about drug resistance?
India has rising rates of MDR (multidrug-resistant) and XDR (extensively drug-resistant) typhoid, especially in Sindh, southern Punjab, parts of North India. Empirical treatment with ceftriaxone, azithromycin, or carbapenem depends on local resistance.
Can children get it?
Yes — paediatric typhoid is common in India. Diagnostic challenges are similar; treatment doses are weight-adjusted.
Related Immunology tests
Tests commonly ordered alongside Typhi Dot IgM, or that help interpret an unexpected result.
Sources & references
- WHO — Typhoid Fever Diagnosis · accessed 2026-05-30T00:00:00.000Z
- ICMR — Typhoid Diagnostic Guidelines · accessed 2026-05-30T00:00:00.000Z
- CDC — Typhoid Fever · accessed 2026-05-30T00:00:00.000Z
- IDSA — Enteric Fever · accessed 2026-05-30T00:00:00.000Z
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