The Leptospira IgG test is your "look-back" test. It measures the long-term "memory" (IgG) antibodies your body produces after a past infection with Leptospirosis (a 'monsoon fever' from contaminated water). A positive result here confirms you have been exposed at some point in your life. To get a complete, actionable answer, your doctor will almost always order this with the IgM test. For your convenience, we recommend our comprehensive Leptospira IgG/IgM Panel, which checks for both past exposure and active infection in one simple blood draw.