The NEXUS vision: an alternative to the reference value concept.

In Lundberg's brain-to-brain turnaround time loop, the postanalytical phase is undoubtedly one of the most difficult phases. Of course, error prolongation can cause serious problems when quality is not sufficiently assessed and assured in the preanalytical and analytical phases. However, in the postanalytical phase following reporting, interpretation and action are at stake; and with this the wellbeing of the patient. Here exists a grey area of responsibility between the laboratory and physician. The laboratory should correctly report the measurement as data. But to place this in the correct context requires additional information on (specific) reference values, specificity, sensitivity and possible interpretation of the data. Here is where the ultimate interaction between the laboratory and the physician (representing the patient) occurs. What happens when errors occur in this phase? Do errors occurring in the previous phases effect this phase? What types of errors occur in the postanalytical phase? Postanalytical quality is the ultimate check on the coherence of the preanalytical, analytical and postanalytical quality; it is a check on the overall quality. It ties together the quality of the question to be answered, the analytical quality that is achieved and the usefulness of the answer obtained. In addition, it also checks quality in the context of the patient and physician interaction. Can errors be avoided and can a predictable quality level be assessed and be assured? A model, called NEXUS vision is described.