What is the cardinal sign of Lyme disease? At what stages of Lyme disease are the IgG and IgM antibodies elevated? 

A rash that is expanding, called erythema migrans or EM (erythema migris), is the cardinal sign for Lyme disease. It appears approximately 7-14 day after a bite by a tick. This rash may be 2-12 inches long and appear at the location of the tick bite. EM may be circular, oval or red in color with a pattern of bullseye. Lyme disease can also cause a fever, swollen nodes and lymph glands, stiffness, pain in the joints, or a headache.

Lyme disease is commonly diagnosed using IgG or IgM antibodies. These antibodies can be detected at higher levels in the later stages of illness, when more precise tests are unable to detect infection. IgM will increase in levels for approximately 4-6 week during early infection. Later, IgG will overtake IgM antibody and stay high for many months. Therefore testing for both classes of antibodies can help confirm diagnosis if performed at multiple time points during an individual’s illness course.