Partial Validations

Periodically changes to a validated assay are necessitated for a variety of reasons. For instance, due to protein binding, it may be necessary to switch from heparin as an anticoagulant to EDTA. This apparently small change to the validated assay may alter its performance and it is necessary to demonstrate whether or not the characteristics of the assay have changed. A full validation is likely not necessary, as a partial validation will suffice to address the question. Unfortunately, the extent of partial validation is left to the discretion of the analyst. Partial validations may range from one intraassay accuracy and precision determination, to almost a complete validation. A reasonable suggestion is that partial validations should basically consist of selectivity, accuracy, and precision determinations. Once this step is completed, the analyst may decide on the need for further validation of the modified assay. Some of the situations where partial validations should be considered are listed in the FDA Guidance. This list is not exhaustive, but it describes the most likely partial validation situations. Some of these scenarios are:

• Method transfer between labs or analysts

• Change in detection system

• Change in anticoagulants

• Change within matrix within species (e.g., human plasma to human urine)

• Change of species within matrix (e.g., rat plasma to mouse plasma)

• Changes in sample processing

• Change in concentration range

• Instrument or platform changes

• Limited sample volumes

• Rare matrices

• Selectivity demonstration of analyte in presence of concomitant medications or in the presence of metabolites

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