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Clinical Insights

Interpreting results with GLI-2012 using Z-score and LLN

Interpretation of Spirometric results

When interpreting test results there is uncertainty about the “abnormality” of a finding near the LLN than if the test result is within the normal range or in a pathological range.

Measured values of FEV1, FVC, FEV1/FVC with additional indices, such as PRE and POST bronchodilator, predicted values, LLN, % of predicted, confuses most users.

Conversely, PICTOGRAMS in which Z–SCORE are depicted relative to a normal range allow a simple interpretation of the spirometric results.

Fig. 3 – Pictograms.

When Z-SCORE is -1.64, it means that the parameter of the spirometry is placed exactly on the LLN that represents the point below which only 5% (5th percentile) of the normal population had a value lower than predicted.

In the center of PICTOGRAM the Z-SCORE is equal to 0, it indicates that the measured value is exactly equal to the predicted one.

In this point we find 50% of the healthy population (the center of the bell).

In conclusion, if a patient has an FEV1 MEASURED = LLN, it means that he is at the limit of the 5th percentile.

Only 5% of the healthy population, with his own anthropometric data, has a lower value. In short, it is still healthy but he is very close to…

…the population considered sick!

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