Most patients with Lyme borreliosis do not recall a tick bite. The saliva of ticks contains a local anesthetic that helps mask their presence while taking a blood meal, and the ticks are also often in the groin, armpit, or nape of the neck and therefore not noticed [“Derm Dx: Is this Lyme disease?”]. The negative blood test is irrelevant. When clinical symptoms of early Lyme disease present, only about one-third of patients have positive serology. With treatment, about another one-third seroconvert, even with successful antibiotic treatment. Another one-third never seroconvert, as the antibiotics eradicate the infection before measurable IgM or IgG levels are present. 

The lesson to be learned is that early Lyme disease is a clinical diagnosis. There is no indication for serology unless you are also drawing blood to check for coinfection with anaplasma or babesia. A negative blood test does not rule out Lyme disease. By the same logic, there is no indication for repeat blood testing, and generally no blood testing is indicated for Lyme disease unless there are symptoms of late disease (eg, neurologic symptoms, arthritis, or cardiac conduction abnormalities).—Vijay Sikand, MD, New London, Conn. (218-1)

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