To ascertain use of serologic tests for Lyme disease (LD) in Maryland, all laboratories registered with the State Health Department were surveyed. Results show that from 1992 to 1995, 17 laboratories performed 100,000 serologic tests costing $7.1 million on Maryland residents; 90% of these tests were EIAs. The proportion of positive EIAs increased from 3.4% in 1992 to Ç7.0% in 1994 and 1995, and the percentage of positive second tests (Western blot, WB) fell from 7.9% to 5.0% -5.5%. The large number of EIAs performed in comparison with the low incidence of LD in the state results in a low predictive value of a positive EIA test. Therefore, the WB is indicated to confirm equivocal and positive EIA tests when characteristic clinical findings of LD are not present. The 30,000 tests for LD performed annually on Maryland residents at a cost of over $2 million in direct medical costs must be added to the public health burden of LD in this state.Lyme disease (LD) is the most common vectorborne illness LD were being performed on Maryland residents. Therefore, we surveyed all laboratories performing diagnostic testing for in the United States and is increasing in prevalence and distribution [1]. The hallmark of early infection, the expanding LD on serum from Maryland residents to estimate the number and types of tests performed and their cost. bull's-eye erythema migrans (EM) rash, is absent in 30% -40% of patients meeting the Centers for Disease Control and Prevention's (CDC) surveillance case definition for LD [2]. Rheumatologic, neurologic, and cardiac manifestations suggesMethods tive of late-stage LD require serologic confirmation, since they The most commonly performed test, an EIA, lacks sensitivity a positive test result to the DHMH, were sent a questionnaire in detecting Borrelia burgdorferi antibodies in the earliest with an explanatory cover letter. The questionnaire inquired about stages of the disease. In patients with late-stage LD, crosswhich tests were performed, the number of tests performed per year, the proportion of positive tests, and charges for performing reactivity during testing lowers specificity and causes confusion the tests. Each laboratory was assured of the confidentiality of its with several infectious and autoimmune diseases [4 -6]. The responses and was assigned an identification number so that results current recommendation is to use a two-test approach to serocould not be traced to specific laboratories. logic testing for LD: the more sensitive EIA test followed byThe survey was mailed to the 27 laboratories identified. Those the more specific Western blot (WB) for those with equivocal that failed to return the survey within 2 weeks were called and and positive EIA test results [4 -6].reminded. Two weeks later, the remaining laboratories wereIn 1992, we began collecting and recording data, including phoned and offered the option of having a project investigator diagnostic laboratory tests, on patients with LD reported to the collect the data from their records. Three chose to be site-v...