Which of the following is NOT a common testing method for diagnosing Lyme disease?

The correct identification of "saline culture" as a method that is not commonly used for diagnosing Lyme disease stems from the nature of the disease and the typical laboratory approaches employed for its diagnosis. Lyme disease, caused by the bacterium Borrelia burgdorferi, is primarily diagnosed through serological tests and molecular methods rather than through culturing methods.

Serum EIA (enzyme immunoassay) testing is a commonly used serological method that detects antibodies against Borrelia burgdorferi in the patient's blood, making it effective for diagnosing active infection or past exposure. PCR testing of skin biopsy is another crucial diagnostic tool that can directly detect the genetic material of the bacteria in skin lesions, particularly in early manifestations of the disease such as erythema migrans. Testing of synovial fluid is also relevant, especially in cases of Lyme arthritis, as it allows for the analysis of joint fluid for evidence of infection.

In contrast, "saline culture" does not represent an established testing method for Lyme disease, as the bacteria are not typically isolated in culture from patients. The emphasis in Lyme disease diagnosis is more geared towards serological testing and direct detection methods rather than culturing organisms, particularly in routine clinical practice.