Beyond successful ISR: case-by-case investigations for unmatched reassay results when ISR passed

Incurred sample reanalysis (ISR) is now commonly practiced in regulated bioanalytical laboratories. With an average ISR success rate of 95% or higher and an increasing number of ISR tests being conducted, more and more situations deserve scientific evaluation or investigation for the unmatched reassay results revealed in ISR tests even though they meet the acceptance criteria. First, should an investigation be initiated when an ISR test is acceptable? How large a discrepancy or what situation would warrant an investigation? What would be the impact on a study? How would investigations regarding unmatched reassay results be conducted? What are the main root causes identified? Can normal random errors cause a large discrepancy in unfavorable combinations? How could the timeline and cost be affected? All these questions are addressed in this paper with five real case examples.