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Investigation of alkaline phosphatase discrepancies on the Roche cobas® pro: causes, solutions, and workflow
I Seiden-Long1, K Niemann2, K Moses2
1Alberta Precision Laboratories, Canada; University of Calgary, Cumming School of Medicine, Department of Pathology and Laboratory Medicine, Canada.
Background:
A high frequency of delta check flags for alkaline phosphatase (ALP) on the Roche cobas® pro revealed non-reproducible and spurious ALP discrepancies. Multi-site studies were performed to characterize discrepancy frequency, identify root causes, and develop mitigation strategies.
Method:
ALP in lithium heparin plasma separator tubes (PST) were measured in duplicate on the Roche cobas® pro c503 at 9 sites and cobas® 8000 c702 at one site. Duplicate results exceeding the total allowable error (TEa: ≤150 U/L ± 15 U/L or > 150 U/L ± 10%) were defined as discrepancies. Three protocols were evaluated over 4-36 weeks: 1) repeat centrifugation and measurement, 2) use of an alternative tube type with cleaner plasma (BD Barricor) and 3) on-board 1:5 dilutions.
Results:
A total of 563 ALP discrepancies were identified across c503 sites, whereas none were observed on the c702. Discrepancy frequency varied by sites (0.04-1.51% of total ALP volumes). Repeat centrifugation improved duplicate agreement and reduced discrepancies by 99.5%. Barricor tubes reduced discrepancies by 81.4%, but did not eliminate them, while dilution reduced discrepancies by 95.4%. An automated protocol combining dilution with respinning completely eliminated discrepancies.
Conclusion:
ALP discrepancies occurred across multiple c503 analyzers but were absent on the c702. The improvements observed with respinning, dilution, and Barricor tubes indicate a preanalytical source of error and suggest that the c503 may be more susceptible to plasma contaminants than the c702. Implementing an automated workflow integrating on-board dilution and additional centrifugation provided a cost-effective, reliable, and streamlined solution to fully mitigate ALP discrepancies.
