In immunoassay screening, what is true about cutoff values?

In immunoassay screening, what is true about cutoff values?

• A. They must always be lower than confirmation cutoffs
• B. They may be higher or lower than confirmation cutoffs; GC-MS often has lower detection limits
• C. They determine the turn-on time of instrument
• D. They have no relation to confirmation testing

Answer: (B)

Cutoff values in immunoassay screening establish the threshold that separates negative results from presumptive positives, guiding which samples proceed to confirmatory testing. These thresholds aren’t fixed relative to the confirmatory test; they can be set higher or lower depending on the desired balance of sensitivity and specificity. In practice, confirmatory methods like GC-MS often have lower detection limits, so they can detect smaller amounts that the screening assay might miss or may confirm positives flagged by a lower threshold. That flexibility—screening cutoffs being able to be higher or lower than confirmation cutoffs, with GC-MS typically offering greater sensitivity—explains why this statement is correct. The other options misstate the purpose or relationship: the cutoff isn’t about instrument turn-on timing, and there is a designed relationship to confirmatory testing in the screening workflow.

Cutoff values in immunoassay screening establish the threshold that separates negative results from presumptive positives, guiding which samples proceed to confirmatory testing. These thresholds aren’t fixed relative to the confirmatory test; they can be set higher or lower depending on the desired balance of sensitivity and specificity. In practice, confirmatory methods like GC-MS often have lower detection limits, so they can detect smaller amounts that the screening assay might miss or may confirm positives flagged by a lower threshold. That flexibility—screening cutoffs being able to be higher or lower than confirmation cutoffs, with GC-MS typically offering greater sensitivity—explains why this statement is correct. The other options misstate the purpose or relationship: the cutoff isn’t about instrument turn-on timing, and there is a designed relationship to confirmatory testing in the screening workflow.