Controversy surrounds the laboratory diagnosis of Lyme disease. Attempts to isolate B. burgdorferi from blood, CSF, or joint fluid have occasionally been successful. However, these methods have not been practical due to the low yield, high cost, and long delay for positive cultures to develop. Urinary antigen testing has not been proven to have diagnostic utility. Serologic studies are currently the only widely used laboratory diagnostic aid for Lyme disease. Initial serologic studies used indirect immunofluorescence (IFA) assays, but these have largely been replaced by enzyme-linked immunosorbent (ELISA) assays. Clinicians should use clinical judgement in making a diagnosis of Lyme disease and use results of a two-step algorithm recommended by a national conference only as supporting evidence. A key element in the diagnosis is a history of outdoor activity in an area known to harbor Ixodes ticks. Assays should not be used to screen asymptomatic patients.

Simultaneous infections can occur with two or more tick-borne infections. Such coinfections have been reported for Lyme disease and both human granulocytic ehrlichiosis and babesiosis.

By treating stage 1 Lyme disease with antibiotics, one can reduce the likelihood that patients will develop later sequelae of Lyme disease. One should reevaluate the diagnosis and then consider repeating treatment if the patient's stage 1 symptoms do not resolve completely after one course of treatment.

Patients with cardiac involvement who have high grade AV block or a first degree AV block with a PR interval greater than 0.30 seconds should be hospitalized and have cardiac monitoring. Treatment with intravenous antibiotics is recommended, and these patients may need to have temporary pacemakers.

Treatment successes with Lyme arthritis have been variable. Approximately 50 percent of patients have complete resolution of their arthritis within several weeks of completing therapy. Among patients treated for Lyme arthritis, success rates have been higher in patients who previously received antibiotics for erythema migrans. In contrast, patients who previously received intraarticular steroid injections are less likely to respond to antibiotics.