Keeping Bacteria Under Control to Minimize Impact on Assays and Maximize Analyzer Uptime

Stephane Mabic1, Maryse Gauthey Baraou1, Johan Thorell2,*

1Lab Water, Merck Millipore, Saint-Quentin-en-Yvelines, France, Saint-Quentin-en-Yvelines, France, 2Merck Chemical and Lifescience AB, Stockholm, Sweden

Introduction: Low bacteria count in pure water is particularly critical in clinical analyzers, because bacteria can generate numerous interferences in biochemistry and immunochemistry assays.

Objectives: The objective here is to describe several of those issues on assays and analyzer maintenance, and provide solutions to avoid bacterial contamination in water supplying the analyzer.

Methods: Typical impacts of bacterial contamination on assays include unstable calibrations, high absorbance of blanks, reference drifts, and errors on mean patient values. Those effects are observed, for instance, on the Arsenazo calcium assay, the potassium potentiometric assay, as well as immunoassays involving alkaline phosphatase (e.g. CTNI, fluorescence 6-MUP- and AMPPD-based assays). Those effects generated by the typical bacteria strains identified in clinical analyzers (Ralstonia pickettii, Sphingomonas paucimobilis, Caulobacter crescentus) result from proteins and small organic acids released by bacteria.

Results: A reduction of two logs is observed on bacteria levels of water treated by germicidal 254 nm UV lamps.

Blank variation in the CTNI assay was shown to decrease over a 30 day period, from a range of 18 to 52 mAU to a range of 20 to 26 mAU by adding an ultrafiltration step to the water treatment process. The ultrafiltration removes the alkaline phosphatase that is released by bacteria, and interferes with the biochemical cascade of the CTNI assay. The stability of the blank ensured a much higher reproducibility of the results and reduced the need for frequent calibrations of the assay.

Conclusion: Maintaining low bacteria level in the analyzer and the water purification system supplying the instrument can reduce downtime and minimize the risks of false results.


Recommendations for the maintenance of the water purification systems are described to ensure a consistent supply of clean water to feed clinical analyzers, in-line with CLSI C3-A4 guideline.

Keywords: Biochemistry