. . "Only a positive Western blot test can confirm the diagnosis of Lyme disease.For many people, the ELISA test remains positive, even after they have been treated for Lyme disease and no longer have symptoms.A positive ELISA test may also occur with certain diseases, such as rheumatoid arthritis.RisksVeins and arteries vary in size, so it may be harder to take a blood sample from one person than anot" . .