The U.S. Food and Drug Administration (FDA) said that that false reactivity, or "false-positive," test results can occur when using the Bio-Rad Laboratories BioPlex 2200 Syphilis Total & RPR kit in some people who received a COVID-19 vaccine.
Based on information provided by the manufacturer, Bio-Rad Laboratories, Rapid Plasma Reagin (RPR; non-treponemal) false reactivity was observed in some patients for at least five months following a COVID-19 vaccination, the FDA said.
“More research is underway to determine the extent of the issue. It is not known if other RPR tests may be affected similarly. Treponemal testing for syphilis such as Treponema pallidum particle agglutination (TP-PA) and treponemal immunoassays do not appear to be impacted by this issue,” the FDA said. “Healthcare providers should make patients who received a reactive RPR result using the Bio-Rad BioPlex 2200 Syphilis Total & RPR test kit aware that they may need to be retested for syphilis with another test to confirm results,” the agency added.
The FDA also released the following recommendations for labs using the test:
- Perform confirmatory testing for all reactive results. Use of only one type of serologic test (non-treponemal or treponemal) for people without an earlier syphilis diagnosis is insufficient for diagnosis.
- In patients with a negative treponemal test (e.g., TP-PA) but reactive RPR result on the BioPlex 2200 Syphilis Total & RPR kit, repeat RPR testing is not necessary unless otherwise clinically indicated.
- For patients previously treated for syphilis in whom treponemal tests remain persistently positive, and who are being evaluated for possible new syphilis infection, a reactive RPR should be interpreted in the context of the patient’s medical history (including COVID-19 vaccination status), risk factors and clinical presentation.
- In patients previously treated for syphilis who received a COVID-19 vaccine and whose clinical presentation and epidemiologic considerations do not support syphilis reinfection, confirm reactive RPR results performed on the BioPlex 2200 Syphilis Total & RPR platform using a different RPR test.
- Sequential serologic tests for patients should be performed using the same testing method (VDRL or RPR), preferably by the same laboratory, to minimize variability. However, if the previously used RPR test was the BioPlex 2200, a RPR test from a different manufacturer should be used at this time.