How are invalid results typically generated in an immunoassay screening?

• A. When the assay fails to produce a valid signal due to instrument error, sample issues, or quality control failure.
• B. When the sample has too much creatinine
• C. When the donor is uncooperative
• D. When the immunoassay is too sensitive causing false positives

Answer: (A)

Invalid results in an immunoassay screening happen when the test cannot generate a reliable signal, making the run uninterpretable. This most often stems from problems with the instrument (like calibration drift, detector or software failures), issues with the specimen itself (insufficient volume, improper storage, degradation, or matrix effects that interfere with the signal), or a quality-control failure (controls outside acceptable ranges, expired or improperly prepared reagents). When any of these occur, the result is flagged as invalid and the assay should be repeated after addressing the underlying problem.

Creatinine levels can hint at specimen quality or dilution, but they don’t by themselves cause an invalid signal. An uncooperative donor affects collection or chain-of-custody, not the analytic validity of the test. If the assay is overly sensitive and yields false positives, that’s a performance issue related to specificity, not an invalid result.