Biologic Chemistry

To mitigate the challenges associated with water contamination as detailed earlier, the College of American Pathologists (CAP), the globally recognized accrediting body for clinical laboratories in the USA, advocates adherence to the Clinical Laboratory Reagent Water (CLRW) standard set by the Clinical and Laboratory Standards Institute (CLSI) as a baseline requirement. Furthermore, instrument feed water should meet the specifications provided by the instrument manufacturer, which might impose more stringent criteria than CLRW standards, ensuring precision and reproducibility of results.

CLRW/CLSI Specifications:

The CLRW resistivity specification, exceeding 10 MΩ-cm, effectively limits ionic impurity concentrations to parts per billion (ppb) levels or lower, necessitating the elimination of carbon dioxide. While this is suitable for most clinical applications, instances requiring trace element determination demand even higher resistivity, reaching 18.2 MΩ-cm. Although CLRW relies on 0.2 μm filters to remove particulates, this may prove insufficient for the extremely low liquid volumes utilized in contemporary clinical assays.

The Total Organic Carbon (TOC) specification of <500 ppb in CLRW, while aligned with earlier standards, may still permit the presence of diverse organic compounds, including carboxylic acids and polyaromatics, posing a potential risk to low-volume assays. Addressing bacterial contamination is equally crucial, as it profoundly impacts analyzer operations, necessitating consistently low contamination levels to prevent biofilm formation and ongoing issues.

Water supplies designated for clinical biochemistry must undergo validation to ensure suitability for their intended purpose. The CLSI emphasizes rigorous trending of water system parameters, underscoring the importance of continuous monitoring to achieve and sustain water purity.