For any highly sensitive DNA or RNA test, a result near the cut-off can reflect contamination, residual nucleic acid from an old infection, or a true early infection. Ask for the Ct value, match it against the clinical picture, and repeat the sample from a fresh site when the result would change management.
- Ask for the Ct value when a PCR result does not fit the clinical picture.
- Repeat the test on a new sample before acting on a weak positive.
- Consider contamination in high-throughput clinics treating many cases of the same infection.
Why it matters
A false positive can lead to unnecessary isolation, treatment and contact tracing.
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