Table. Number and percent positive for Lyme disease tests performed by a large commercial laboratory and percent decrease in 2020 compared with 2019, United States*.
| Testing tier | 2019 |
2020 |
% Decrease in testing volume (95% CI) | Absolute difference in % positive (95% CI) | |||
|---|---|---|---|---|---|---|---|
| Total tests | % Positive | Total tests | % Positive | ||||
| First tier† | 925,939 | 9.6 | 691,453 | 9.2 | 25.3 (25.2–25.4) | 0.3 (0.2–0.4) | |
| Second tier‡ |
422,801 |
11.0 |
|
320,616 |
10.2 |
24.2 (24.1–24.3) |
0.8 (0.6–0.9) |
| Total | 1,348,740 | 10.0 | 1,012,069 | 9.5 | 25.0 (25.1–24.9) | 0.5 (0.4–0.6) | |
*Percent positive indicates the percentage of the total laboratory tests that were positive for each test tier and overall. The percent decrease in testing volume shows the percentage decrease in total tests performed by tier and overall for 2020 compared with 2019. Two-tier testing for Lyme disease is recommended, whereby specimens positive or equivocal on the first tier are subjected to the second tier. Additional details about testing tiers are available at https://www.cdc.gov/lyme/diagnosistesting/index.html.
†First-tier tests include enzyme immunoassays for IgM/IgG combined, IgM alone, and C6 antigen.
‡Second-tier tests include immunoblot for IgM or IgG.