Beware of carryover in modern chemistry analyzers

Random-access analyzers that employ dedicated probes may be affected by carryover. Sample carryover, involving analyte from one sample that is measured in a subsequent sample, is most often detected in measurement procedures that have wide reportable ranges. However, reagent carryover can be more difficult to detect as it may involve only one pair of measurement procedures.

Our laboratory noted several patient samples with total cholesterol <2.58 mmol/L (100 mg/dL) during the initial months after a new chemistry analyzer was installed. The problem seemed to occur intermittently, approximately once per week.

Immediate reanalysis of affected samples resulted in measured values that were 1.03-2.58 mmol/L (40-100 mg/dL) higher. Evaluation of reagent carryover revealed a significant decrease in total cholesterol after analysis of creatine kinase (EC 2.7.3.2). Carryover disappeared when an additional reagent probe wash was applied, whereas the root of the problem was eliminated with replacement of the reagent probes. The insidious nature of reagent carryover made it difficult to initially detect the problem, which affected two of the three instruments in our laboratory.

Laboratorians should be aware of the potential for carryover in random access analyzers, and should be mindful of appropriate troubleshooting techniques.