08/23/2022: Lab Advisory: Mpox Virus Testing Considerations to Prevent False Positive Test Results
Audience: Clinical Laboratory Professionals
Level: Laboratory Advisory
To prevent false positive test results, CDC recommends that laboratory professionals perform repeat testing to verify positive diagnostic results for Orthopoxvirus or mpox virus DNA in specimens with high Cycle Threshold (Ct) values from persons who do not meet identified epidemiologic risk criteria for mpox.
Review laboratory test results (including raw data, PCR curves, etc.) carefully before you report results. Because molecular tests (e.g., real-time PCR tests) are very sensitive, cross-contamination is possible. If you obtain a high Ct value (generally ~34 or higher), CDC recommends to immediately re-extract and re-test to ensure there was no cross-contamination. CDC suggests this approach based on high Ct value alone, even in the absence of epidemiologic information. When possible, re-extract and re-test before you report results. Obtain approval from your CLIA director before you implement this recommendation in your laboratory.
Refer to the Health Alert Network (HAN) Health Update for more information on testing for mpox.
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- Mpox Information for Laboratory Personnel
- How to Report Results from Orthopoxvirus, Non-Variola Orthopoxvirus, and Mpox Virus Laboratory Diagnostic Testing
- Laboratory Procedures and Biosafety Guidelines
- U.S. Mpox 2022: Situation Summary
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