Understanding Changes to Lung Function Test Reports

An important part of managing cystic fibrosis is understanding how well your lungs are working now and over time. Lung health is often measured by a pulmonary function test (PFT) called spirometry. You may notice changes to your PFT results, as the way certain PFT results are calculated is changing in some cases.

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Summary

Many pulmonary function test (PFT) labs are using a new equation to calculate % predicted results. If your PFT lab uses the new equation, your % predicted number may go up or down.
This change does not mean that your actual (absolute) lung function has changed.
Your care team can help you understand what any changes mean for you.

What Is Changing?

To see how well your lungs are working, your care team uses your pulmonary function test (PFT) results. They compare your lung function to people who have healthy lungs but are like you in age, height, sex at birth, and race. This comparison is called % predicted.

We now know that comparisons using race can lead to incorrect readings of lung health. Removing race from the equation gives a better comparison of lung function for your age, height, and sex at birth.

Many PFT labs are changing to a race-neutral equation called GLI 2022. It is called GLI 2022 because the equations were developed by the Global Lung Function Initiative (GLI).

If your PFT lab uses the race-neutral equation, the change may affect your % predicted number. But the measurement of your actual (or “absolute”) lung function will not change. This is the amount of air you blow out as measured in liters (L).

Below is an example. Your % predicted may go up or down. Absolute lung function will not change.

	Old Equation (GLI 2012)	New Equation (GLI 2022)	Change
Absolute Lung Function in Liters (FEV₁)	3.5 L	3.5 L	None
FEV₁ % Predicted	88%	78%	Decrease of 11%

These values are an example only and do not reflect the results of an actual person with CF.

Talking With Your CF Care Team About the Change

Your CF care team can help you understand any changes in your spirometry report. Ask a member of your CF care team, like your respiratory therapist or pulmonologist, to review your spirometry report with you. You may want help understanding:

Compared to people like me who do not have CF, are my lungs better, worse, or the same?
Compared to my earlier results, are my lungs better, worse, or the same?
Based on these new % predicted numbers, what, if any, changes should be made to my treatment plan?
Based on these new % predicted numbers, will my ability to take part in clinical trials change?

Together with your CF care team, understanding your lung function can help you manage your health.

Anxiety and PFT Tests

Many people with CF experience anxiety related to PFTs, and changes to PFT results can increase this anxiety. Talk with your CF care team if you feel anxious about taking a PFT or seeing your test results. The below resource and personal stories may also be helpful:

Guide: Procedural Anxiety
Blog: 4 Tips for Combatting PFT Anxiety
Blog: I’m More Than My Lung Function

More Resources

Printable handout with information from this webpage in English and Spanish.
Pulmonary Function Tests — An overview of PFTs from the American Thoracic Society.
CF Care Center Visits — What happens during a typical visit.

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Care Team | Diversity, Equity, and Inclusion