The Z score is instead a description of how far a result is from the mean value and therefore emphasizes the probability that a result is normal or abnormal. The LLN primarily emphasizes only whether a result is normal or abnormal. The difference between the two however, is in the emphasis each places on how results are analyzed. Both the Z score and the Lower Limit of Normal (LLN) come from the same roots and in that sense can be said to be saying much the same thing.
The use of Z scores to report PFT results, both clinically and for research is occurring more and more frequently.
