Finding the right tests…
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Finding the right tests…
Serology
This test detects two different antibodies your immune system makes against Salmonella Typhi, the bacterium behind typhoid fever, and reports them separately rather than as one number. IgM antibodies tend to appear earlier in an infection and fade over weeks to months, while IgG antibodies typically appear a little later but can stay detectable for much longer, so a positive IgM leans toward a recent or current infection, while a positive IgG alone can reflect exposure from a while back rather than illness happening now. It's a different method from the older Widal test, which measures a different set of antibodies using a slower, tube-based technique rather than the rapid format most IgG/IgM typhoid tests use today. Because antibody tests of any kind can be affected by past exposure, results are read alongside your symptoms and how long you've been unwell, not as a stand-alone answer.
The test reports IgM and IgG results separately, usually as positive or negative, sometimes with a rough indication of strength. A positive IgM result suggests your immune system is currently, or very recently, responding to a Salmonella Typhi infection, since this antibody type rises early and fades over weeks to months. A positive IgG result shows your immune system has encountered the bacterium at some point, which could mean a current infection but could equally reflect a past one, since IgG persists for considerably longer. Seeing both together, and how each changes if the test is repeated, gives more information than either result checked once on its own.
Rapid IgG/IgM typhoid tests work as lateral-flow immunoassays, similar in format to a home pregnancy test, where a drop of blood moves across a strip coated with Salmonella Typhi antigens, and a coloured line appears if matching antibodies are present. This format is faster than the tube-based Widal method and doesn't need a laboratory incubation step, which is part of why it's widely available even outside hospital settings.
A systematic review pooling multiple studies of antibody-based typhoid tests found sensitivity and specificity varying widely depending on the specific test kit and the population it was studied in. Some combined IgG/IgM assays performed strongly in outbreak settings, correctly identifying essentially all confirmed cases in one such study, while others performed considerably less consistently across different studies. What was more consistent across the pooled studies was a high negative predictive value, meaning a negative result was fairly reliable for ruling typhoid out, even though a positive result needed more caution given how much sensitivity and specificity varied by kit.
Because IgG can persist for months to years after an infection has cleared, a positive IgG result doesn't necessarily mean typhoid is causing your current symptoms. It can reflect a past infection or, in areas where typhoid is common, background exposure. Cross-reaction with antibodies from other, unrelated infections is another recognised source of false positives with these tests. IgM is a more time-limited signal, but it can still take some days into the illness to become reliably detectable, since your body needs time to mount that response in the first place.
Because of these limitations, this test is generally used alongside a doctor's assessment of your symptoms and how long you've had them, rather than as the sole basis for a typhoid diagnosis, and blood culture remains the more definitive method where it's available. The sample itself is a routine blood draw.
A positive IgM leans toward a recent or current infection, since this antibody rises early and fades within weeks to months. A positive IgG can reflect either a current infection or one from a while back, since it persists for much longer.
Widal uses an older, slower, tube-based technique measuring a different set of antibodies, while most IgG/IgM typhoid tests today use a faster lateral-flow format that doesn't need a lab incubation step.
Yes. IgG can stay detectable for months to years after an infection clears, so a positive IgG alone doesn't confirm an active infection is causing your current symptoms.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Pooled study data generally shows a high negative predictive value for these tests, meaning a negative result is fairly reliable for ruling typhoid out, though your doctor will still weigh it against your symptoms.
Yes, cross-reaction with antibodies from other, unrelated infections is a recognised source of false positives with typhoid antibody tests.
It can take some days into the illness for IgM to become reliably detectable, since the body needs time to mount that antibody response after infection begins.
Blood culture is generally considered the more definitive method for confirming typhoid, though it takes longer to return a result than an antibody-based test does.
That's worth confirming with your doctor or the centre directly, particularly if other tests are being ordered alongside this one on the same visit.
Since both tests have different strengths and limitations, ordering them together can give a doctor more confidence in interpreting a result than relying on either test alone.