Interpreting results with GLI-2012 using Z-score and LLN
The benefits of Z-Score
The LLN value can also be expressed as a percentage of the PREDICTED:
1) In a healthy person, 20 years old: LLN of FEV1 = 80% of his PREDICTED
2) In a healthy person, 80 years old: LLN of FEV1 = 66% of his PREDICTED
It is clear that the true LLN, when expressed as %PREDICTED, varies considerably with the age. FEV1 value of 66% of the PREDICTED may be fine in a 80 years old person but it would be abnormal for a 20 years old person!
Therefore evaluate a respiratory disease according to the calculation method% PREDICTED is a very popular but should be replaced by the method of the Z-SCORE.
The benefit is that Z–SCORE is completely independent of age, height and sex.
For example, if the Z–SCORE for any parameter is –1.64, this signifies in males, females, children and adults that the measured value is at the 5th percentile.
In lung function testing this is regarded as the LLN.