Multicentre evaluation of Normotest performance characteristics. Interlab variation, comparison of manual and...

Normotest (NT) is a standardized reagent sensitive to changes in concentration of factors II, VII and X. It has been proposed as a useful screen for the liver synthetic function. We carried out a multicentre study aimed to compare in 5 different labs variability and reproducibility of results, normal ranges and manual versus instrumental techniques. NT values were significantly different in the 5 labs, regardless of how the results were expressed. However, within each lab, the results of manual and instrumental techniques were usually not different, providing they were expressed as ratios of test to reference plasmas. Within-lab, between-day reproducibility was much greater when results were expressed as than as %s; reproducibility was also greater with the instrumental than with the manual technique. With both techniques, normal ranges established in each lab were much more uniform when the results were expressed as ratios than as %s. On the whole, this study suggests that NT results should be expressed as ratios, that instrumental techniques should be preferred to manual techniques, and that each lab should establish its own normal range.