If a positive immunoassay is not corroborated by confirmatory testing due to cross-reactivity, how should the lab proceed?

If a positive immunoassay is not corroborated by confirmatory testing due to cross-reactivity, how should the lab proceed?

• A. Report the result as positive regardless of confirmatory outcome.
• B. Report the result as negative or invalid per confirmatory outcome; if confirmatory is negative, no positive result is issued; consider reviewing cross-reactivity and updating screening cutoffs.
• C. Ignore the discrepancy and proceed with the patient as positive.
• D. Retest the same sample twice and report the majority result.

Answer: (B)

When a screening immunoassay yields a positive but the confirmatory test does not corroborate it, the final result should reflect the confirmatory finding. Immunoassays are designed to be sensitive, but they can cross-react with substances that resemble the target, leading to false positives. The confirmatory test is more specific and serves as the definitive result. If the confirmatory result is negative, no positive result should be issued. If cross-reactivity is suspected, review the assay’s known cross-reactants and consider adjusting screening cutoffs or updating the testing method to reduce future false positives.

When a screening immunoassay yields a positive but the confirmatory test does not corroborate it, the final result should reflect the confirmatory finding. Immunoassays are designed to be sensitive, but they can cross-react with substances that resemble the target, leading to false positives. The confirmatory test is more specific and serves as the definitive result. If the confirmatory result is negative, no positive result should be issued. If cross-reactivity is suspected, review the assay’s known cross-reactants and consider adjusting screening cutoffs or updating the testing method to reduce future false positives.