The IgM antibodies are the first antibodies to be produced in the body in response to an infection. IgM antibodies are larger than IgG antibodies and when present in high numbers, may indicate a recent or new active infection. In short, a positive IgM may be a sign of a current, or very recent, infection. The IgG antibodies are produced once an infection has been going on for a while, and may even be present after the infection has been resolved. The presence of IgG antibodies to an organism when accompanied by a negative IgM test for the same organism means that the person was exposed to that organism at one time and developed antibodies to it, but does not have a current active infection of that organism. People who test positive by IgM but not IgG should have the test repeated a few weeks later if they remain ill. If the person is positive only by IgM and has been ill longer than one month, this is likely a false positive result for Lyme disease.