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Blood Test Tracker

Salmonella Typhi IgM (Typhoid Antibody)

A blood test for IgM antibodies to the typhoid bacterium. On its own it cannot confirm typhoid fever.

AI-verified against cited sources. Awaiting expert reviewAlso called Typhi IgM, S. Typhi IgM

What it is

Typhoid (enteric) fever is an infection caused by Salmonella Typhi bacteria, usually spread through contaminated food or water. This test looks for IgM, an early-type antibody your immune system makes against the bacteria. It is done in several ways: a quick card or dot test (such as Typhidot), a Tubex TF test that gives a score from 0 to 10, or a lab ELISA that gives an index. Results are printed as negative, borderline or positive, or as a score. The method used matters, so keep it with the result.

Why it matters

In places where typhoid is common, rapid antibody tests like this are sometimes used because they are quick and low cost. They are not accurate enough to stand alone. Reviews found that these rapid antibody tests miss a share of people who have typhoid and flag some people who do not. CDC notes that antibody tests cannot tell a current infection from a past one or from vaccination. Blood culture remains the preferred test to confirm typhoid. Your result is best read together with your symptoms, how many days you have been ill and any culture result.

If it’s high

A positive result means antibodies against Salmonella Typhi were found. This can happen with a current typhoid infection, but also after a recent past infection or typhoid vaccination, and these tests can give false-positive results. A positive result alone does not confirm typhoid fever. Your clinician will weigh it with your symptoms and, if possible, a blood culture.

Common causes

  • Current typhoid (enteric) fever
  • A recent past typhoid infection or exposure
  • Typhoid vaccination (CDC says antibody tests do not separate this from infection)
  • A false-positive result, since these tests lack specificity (CDC)

What can help

  • Ask whether a blood culture is needed to confirm the diagnosis
  • Ask what to watch for at home and when to come back
  • Wash your hands with soap and water after using the toilet and avoid preparing food for other people while you are ill, to protect those around you (WHO)
  • Ask about typhoid vaccination for the future (WHO)

What can affect your result

  • Timing in the illness: antibodies take time to build, so a very early sample can be negative
  • Test kit: Typhidot, Tubex TF and lab ELISAs use different methods and cutoffs
  • Past infection or typhoid vaccination can leave antibodies that confuse the result
  • Place and population: accuracy differed between study sites in a 2022 multicenter study
  • Antibiotics before sampling can lower the yield of a blood culture (BMJ 2021)
  • Past typhoid infection or typhoid vaccination can leave antibodies, and CDC says antibody tests do not separate these from a current infection.
  • The kit matters: Typhidot, Tubex TF and lab ELISAs use different methods and cutoffs, so results from different kits are not interchangeable.
  • In one multicenter study, the sensitivity of the IgM part of a Typhidot rapid test was 32.7% at one site and 93.2% at another, so accuracy can vary by place and population.
  • Antibiotics taken before a blood culture is drawn lower the chance that the bacteria grow (BMJ 2021), which is one reason antibody tests are used when culture is unavailable.

IgM points to current or recent exposure (Cochrane 2017), but antibodies take time to build, so a very early sample can be negative.

When to talk to a clinician

Typhoid fever needs medical care. See a clinician promptly if you have a fever that lasts more than a few days, especially with stomach pain, headache, weakness, constipation or diarrhea, or after living in or travelling to a place where typhoid is common. Get urgent care or call your local emergency number for severe belly pain, confusion, repeated vomiting, a high fever that does not come down, or fainting. Untreated typhoid can be serious (CDC).

Questions you could ask

  • Which typhoid test did I have (Typhidot, Tubex or another), and how reliable is it?
  • Should the test be repeated if my fever continues?
  • Should I have a blood culture to confirm the diagnosis?
  • Could this result reflect a past infection or a recent typhoid vaccine?
  • What should I watch for at home, and when should I come back?

Questions people ask

Can this test confirm that I have typhoid?

No. A positive IgM supports a diagnosis but does not prove it, because these tests can give false positives and cannot separate a current infection from a past one or from vaccination. Blood culture is the preferred test to confirm typhoid.

What is the difference between Typhi IgM and IgG?

IgM points to a current or recent infection. IgG can reflect a current, recent or older exposure, so an IgG-only result is harder to read. Some rapid kits report both. IgG is reported as a separate result.

Why might my doctor still order a blood culture?

Blood culture is the preferred way to confirm typhoid and also shows which antibiotics will work. A single culture finds the bacteria in only about half of cases (CDC), so a negative culture does not completely rule it out, and antibiotics taken before the sample lower the chance of growing the bacteria.

Show the science and sources

For clinicians and researchers

Typhidot is a dot-ELISA that separately detects IgM and IgG against a Salmonella Typhi 50 kDa outer membrane protein; in accuracy studies, IgM alone or IgM plus IgG counts as positive and IgG alone as indeterminate. Tubex TF is an inhibition immunoassay in which patient IgM competes with monoclonal antibodies for binding to the Salmonella Typhi O9 lipopolysaccharide, read as a color score from 0 to 10. The manufacturer calls a score of 4 weakly positive and 6-10 positive, and studies use cutoffs of 3, 4 or 6. In the 2017 Cochrane review, TUBEX had an average sensitivity of 78% (95% CI 71-85) and specificity of 87% (82-91) in 14 studies. All Typhidot forms together averaged 84% sensitivity (73-91) and 79% specificity (70-87), or 78% and 77% in studies that reported indeterminate results. The review concluded these tests are not accurate enough to replace blood culture. CDC states that a single blood culture is positive in roughly 50% of cases, bone marrow culture reaches about 80%, and serologic tests do not distinguish acute from past infection or vaccination and lack specificity. IgM is indicative of current or recent infection, while IgG can reflect current, recent or previous exposure. The Widal test is a different, agglutination-based antibody test (a separate test). Results from a rapid card or a Tubex score should be stored with the method name. No serum Salmonella Typhi IgM LOINC code was found in the NLM LOINC search.

Sources

  1. Rapid diagnostic tests for typhoid and paratyphoid (enteric) fever, Cochrane Database of Systematic Reviews (2017)
  2. Enteric fever, BMJ (2021)
  3. Typhoid and Paratyphoid Fever (CDC Yellow Book), CDC
  4. Typhoid (fact sheet), World Health Organization
  5. A systematic review and meta-analysis of the performance of two point of care typhoid fever tests, Tubex TF and Typhidot, in endemic countries, PLoS One (2013)
  6. Clinical characteristics of enteric fever and performance of TUBEX TF IgM test in Indonesian hospitals, PLoS Neglected Tropical Diseases (2024)
  7. Comparative Analysis of Commercially Available Typhoid Point-of-Care Tests: Results of a Prospective and Hybrid Retrospective Multicenter Diagnostic Accuracy Study in Kenya and Pakistan, Journal of Clinical Microbiology (2022)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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