Abstract
The letter from Dr Dittadi clearly illustrates the importance of considering information from each patient instead of data from a non-homogenous comparison group for the follow-up of patients. The reference change value, that is the difference between two consecutive results of the same analyte from the same person (also known as the critical difference) is a widely accepted method for detecting significant changes of patient status.
Data from within-subject biological variations are the basis for defining the value that reflects a change and it is important to know that in some cases, this value should not be derived from the healthy population, due to different homeostatic regulation in quite a few non-healthy situations. We were aware of this fact and published a revision that put on the table evidences of this reality.
Thus, I think that efforts in this respect are very worthwhile and help clinical laboratory professionals towards improving the utility of their reports. This, consequently, enhances the quality of the health-care system.