Finding the right tests…
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Finding the right tests…
Serology
LEPTOSPIRA IGG looks for a longer-lasting antibody made once your immune system has fully responded to a Leptospira infection, the bacteria spread through water or soil contaminated by infected animal urine. IgG typically takes longer to develop than IgM, so it becomes more useful later in an illness, or when your doctor is comparing a sample from now against one from a few weeks ago to confirm the infection actually happened. On its own, a single IgG result mainly reflects that your immune system has mounted a full response at some point, without pinpointing exactly when your illness began. It's typically read together with an IgM result or a paired convalescent sample rather than in isolation.
A Leptospira IgG result is reported as positive or negative, and because IgG rises later in the illness than IgM, its timing carries a different meaning from an IgM result. Confirming that IgG has genuinely risen, rather than reflecting an old exposure, usually needs a second sample compared against the first. It's more useful once you're further into a suspected leptospirosis infection or being retested a few weeks after an earlier sample than in the first few days of fever. A single blood draw is enough for each sample, with no special preparation needed.
IgG is the more durable antibody your immune system builds once it has had real time to respond to an infection, and with leptospirosis it typically becomes detectable later in the illness than IgM does. Because of this delay, IgG is less useful for catching leptospirosis in its earliest days and more useful for confirming that an infection genuinely happened, especially when read against an earlier sample.
A positive IgG on its own shows your immune system has responded to Leptospira exposure, but it can't say precisely when that happened, since IgG generally stays elevated for some time after the acute illness has passed. This is why doctors typically use it as part of a paired comparison — a convalescent sample taken some weeks after an earlier one — to confirm a rising antibody level rather than relying on a single value.
The reference confirmatory test for leptospirosis, the microscopic agglutination test, actually measures a combination of IgM and IgG-type antibodies together rather than IgG in isolation, and needs either a very high single titre or a clear rise between paired samples to count as confirmed. Your doctor typically weighs an IgG result alongside your IgM result, symptoms, and possible exposure history.
Not necessarily on its own. IgG shows your immune system has responded to Leptospira exposure at some point, but confirming a current infection usually needs it compared against an earlier sample or read alongside IgM.
IgG generally takes longer to develop than IgM, so it becomes more informative once you're further into the illness or being retested weeks after an earlier sample.
It's the reference confirmatory test for leptospirosis, and it actually measures a combination of IgM and IgG-type antibodies together rather than IgG alone, requiring either a high single result or a clear rise between paired samples.
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.
Comparing two samples lets your doctor confirm that antibody levels have genuinely risen, which distinguishes an active, ongoing response from an old exposure.
Not reliably by itself. It's usually read alongside your IgM result, symptoms, and possible exposure history, or compared against an earlier sample, rather than used in isolation.
No. No special preparation, including fasting, is needed before this blood draw.
Most commonly through contact with water, soil, or surfaces contaminated by the urine of infected animals, with risk rising after flooding or heavy rain, according to CDC guidance.