Factors affecting test reproducibility among laboratories

Reproducibility is the ability of an assay to provide consistent results (when testing the same samples) in different laboratories. The validation of a new diagnostic assay should include specific assessment of assay reproducibility to determine the degree to which results are unaffected by minor changes in experimental conditions. Ideally, assessment of reproducibility involves the testing of identical samples in multiple laboratories by multiple analysts using the same method, reagents and controls, albeit with different equipment. Such an assessment will provide estimates of the precision and accuracy of an assay across laboratories. In reality, although the reproducibility of an assay is often assessed by multiple laboratories testing identical samples, the reagents, controls and testing platforms used, while similar, are usually not the same. Thus, reproducibility testing permits the assessment of variability resulting from different testing platforms, reagent supplies and operators. The determination of minor versus major variations in test conditions that may be anticipated in multi-laboratory use is part of the assessment at this stage of validation. Once validated, there are ongoing monitoring requirements to assess the performance characteristics and ensure they are consistently maintained. The use of quality assurance programmes is required, as this offers continued monitoring of assay performance by measuring the precision and accuracy of results for well-characterised samples and controls. Tests recommended by the World Organisation for Animal Health as fit for purpose are widely used internationally and need to have satisfactory reproducibility.