What test would a doctor likely order next if a patient has inconclusive ELISA tests for Lyme disease?

The Western blot test is a more specific confirmatory test for Lyme disease following inconclusive results from an ELISA test. The ELISA is commonly used as an initial screening tool due to its ability to detect antibodies against Borrelia burgdorferi, the bacteria that causes Lyme disease. However, some patients may have inconclusive results from ELISA due to various factors, such as timing of the test or individual immune responses.

In this context, the Western blot test is utilized to confirm the presence of specific antibodies that indicate an active infection. It involves separating the proteins of the bacteria and then detecting antibodies that bind to those proteins. This test has a higher specificity and can differentiate between false positives and true infections more effectively than the ELISA.

The other tests listed serve different purposes. The RPR test is typically used for syphilis screening, the FTA-ABS test is also aimed at syphilis but is not typically related to Lyme disease diagnosis, and the complement fixation test is more often used for various infections but is not commonly used for Lyme disease specifically. Therefore, ordering a Western blot test after inconclusive ELISA results is the logical next step in confirming or ruling out Lyme disease.