Validation and verification of automated urine particle analysers.

There is often uncertainty on how validation and verification of newly introduced tests should be conducted, and there is a real risk of verification becoming a meaningless ritual, rather than a useful exercise. This article reviews the literature and makes recommendations regarding the validation and verification of automated urine particles analysers. A generic practical approach to verification is also recommended. For many analysers, the accuracy of white blood cells, epithelial cells and bacterial counts is corroborated by a number of independent evaluations; thus, any verification laboratory work could be significantly scaled down. Conversely, in the scenario that automated urine microscopy is used as a screening test to reduce the number of urines cultured, the extremely variable performance reported in the literature requires a full-scale verification to define the optimal cut-off values that give a sensitivity of >98% with the local settings and circumstances. With some analysers, the risk of carry-over also needs to be assessed, as part of the verification process, and exclusion criteria (urines requiring culture regardless of the microscopy results) need to be well defined, as there are patients or specimen types for which the performance of microscopy as a screening test may not be adequate.

Flow cytometry for the microscopy of body fluids in patients with suspected infection.

Automating the microscopy of body fluids is challenging, due to the wider range and lower concentrations of cells in these fluids, as opposed to blood, while the viscous nature of some of these fluids can also be problematic. This review shows that there have been major improvements and that newer flow cytometers can have remarkably low limits of quantitation for WBCs. Accurate counting of RBCs is still problematic with many flow cytometers, but this is of no clinical significance. Many flow cytometers can give reasonably accurate WBC differential counts, but detection of eosinophils and neoplastic or other nucleated cells which are not blood cells can still be problematic, hence fail-safe measures are recommended. Cerebrospinal fluid is the most challenging body fluid as it requires the ability to count and differentiate WBCs down to a 'normal range', which is much lower than the diagnostic cut-off values used for serous fluids; precision at or around the cerebrospinal fluid WBC normal range is reduced even with the best flow cytometers, but manual microscopy is even less precise.