Changes to Lyme disease testing

Advisory Alert

March 9, 2023

*Cette information est seulement disponible en anglais.

To: Family Physicians, Nurse Practitioners


As of April 1, 2023, the Public Health Ontario Lab will be using a new testing algorithm for Lyme disease.

The current model uses a standard two-tier testing model. In this model, samples are tested for total IgM/IgG antibodies by enzyme-linked immunosorbent assay (ELISA). Any samples that are reactive or indeterminate are sent for further testing using an IgM/IgG Western blot assay.

During early, localized Lyme disease, however, the sensitivity of the current model is low, ranging from 29 to 40 percent. As such, a negative test result does not rule out Lyme disease infection. Due to poor sensitivity of test results, most early localized Lyme disease infections are primarily diagnosed on clinical presentation consistent with Lyme disease and with tick exposure risk.

The new algorithm will implement a modified two-tier testing approach. This new approach uses a second ELISA instead of the Western blot assay. Using the second ELISA provides 15 to 25 percent higher sensitivity during early localized disease, and comparable sensitivity during early disseminated and late-disseminated disease. The specificity is also comparable to the current method.

The changes in testing algorithm will help to improve Lyme disease diagnosis in early localized disease (by reducing the chances of a false-negative result) and help to increase the turnaround time for Lyme disease testing, leading to earlier intervention. The testing algorithm doesn’t replace clinical decision making and is intended to support clinical decision making by increasing the sensitivity of the test and improved turnaround time for test results.

Please visit Public Health Ontario for additional resources, including Lyme disease risk areas, at

For questions related to Lyme disease, please contact our Environmental Health program at 705.522.9200, ext. 464 (toll-free 1.866.522.9200).


Original Signed By

Dr. Marlene Spruyt

Acting Medical Officer of Health

On behalf of Dr. Penny Sutcliffe Medical Officer of Health and Chief Executive Officer


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This item was last modified on March 9, 2023