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Finding the right tests…
Serology
LEPTOSPIRA IGM checks your blood for an early antibody your immune system makes against Leptospira bacteria, spread through contact with water or soil contaminated by infected animal urine. This antibody is what a screening ELISA test looks for during the first couple of weeks of illness, when leptospirosis can look like several other causes of fever. Its sensitivity depends heavily on timing — one antibody drawn very early in illness is less likely to catch a true infection than one drawn after the first week, once your immune system has had more time to respond. A positive result on this screening test is usually followed by a confirmatory test at a reference laboratory before treatment decisions rely on it alone.
Leptospira IgM comes back as a positive or negative reading based on a screening method such as ELISA. Its sensitivity rises the longer you've been unwell — one study found it detected only around half of true infections in the earliest blood sample, rising to roughly 90% in a sample taken later in the illness. Because of this, a negative result taken in the first few days doesn't rule out leptospirosis, and your doctor may repeat testing later. A single blood sample is enough, with no special preparation needed.
Leptospirosis is caused by Leptospira bacteria, which spread to people through contact with water, soil, or surfaces contaminated by the urine of infected animals such as rodents or cattle — contact that often increases after flooding or heavy rain. IgM is the first antibody your body produces in response, and this test screens for it using a method such as ELISA.
Antibody levels take time to rise, so a sample taken in the very first days of illness may still show no antibody even in someone genuinely infected. Studies comparing samples taken at different points in the same illness have found IgM detection rates around half in the earliest sample, climbing to roughly 90% in samples taken further into the illness — which is why a single early negative result isn't considered enough to rule leptospirosis out.
A reactive IgM screening result is usually followed by a more specific confirmatory test, called the microscopic agglutination test, run at specialised reference laboratories, since screening tests alone can occasionally give a false positive. Your doctor weighs your IgM result alongside your symptoms, possible water or animal exposure, and other blood findings before confirming the diagnosis.
It spreads through contact with water, soil, or surfaces contaminated by the urine of infected animals such as rodents or cattle, and risk rises after flooding or heavy rain, according to CDC guidance.
Sensitivity is lower in the first few days of illness and improves later — one study found detection around half the time in the earliest sample, rising to roughly 90% in a later sample.
A positive screening result is usually followed by a more specific confirmatory test, called the microscopic agglutination test, run at a specialised reference laboratory.
Screening tests like IgM ELISA can occasionally give a false positive, which is why a reactive result is generally confirmed with the microscopic agglutination test before treatment decisions rely on it alone.
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.
Because antibody levels take time to rise, a sample taken early in your illness can miss a true infection; repeating the test later, once your immune response has developed further, improves detection.
Yes, the microscopic agglutination test is considered the reference standard for confirming leptospirosis, though it's only available at certain specialised laboratories.
No. No special preparation, including fasting, is needed before this blood draw.