Plot of ECCS FEV1 data for men

GOLD v LLN    Page 3

How does GOLD define an abnormal FEV1?

   GOLD states that if the FEV1 is below 80% of the predicted value then this is an abnormal result. Furthermore they go on to define degrees of abnormality based on set levels of percent of predicted. FEV1 declines with age and is larger for those of greater height. The Figure to the right shows a random sample of FEV1 for men that fits the ECCS prediction equation and all have the mean height for the group. The LLN declines with age but not in proportion to the predicted and so the GOLD cut off of 80% of predicted is incorrect. The red dots are subjects with results below the LLN and the mid blue dots are those that GOLD says are abnormal but are in fact above the LLN (false positives) and the dark blue dots are subjects GOLD says are normal whereas they are below the true LLN (false negatives).

Plot of ECCS FEV1 data for women

   So the GOLD cut off for defining an abnormal FEV1 overestimates the number of subjects with abnormalities and this effect is greater in older subjects.

   To the right is the same plot as above but for females and it can be seen that the age where false positives start is again a bit older in the females and there are proportionately slightly more female subjects that GOLD says are normal (dark blue dots) but who are in fact below the LLN and so are false negatives.