Please note: While some information will still be current in a year, other information may already be out of date in three months time. If you are in any doubt, please feel free to ask.

lung function

i have been told my lung function is a third of predicted, does this mean my lung function is around 33%?

Thank you for your question. You are correct if you have been told by your clinician that your lung function is a third of predicted this would mean that your lung function is around 33%.

Lung function is an important measure that enables clinicians to monitor your cystic fibrosis disease, this is supported in the European Guidelines (Reference found below). When you perform lung function tests the results are usually given as raw data (litres, litres per second) and percent predicted based on how you compare to your predicted value. The test result given as a percent of the “predicted values” is based on a person of similar characteristics (height, age, sex and sometimes weight and race). Generally speaking lung function results of 80 % predicted and above are considered normal and as this percentage falls, this is indicative of airways disease. To get a more detailed account and interpretation of your lung function values please consult your CF clinician the next time you are performing lung function.

The technician or clinician that performs your lung function test has strict guidelines they must adhere to. An outline of these guidelines can be found in the reference below.

Kerem E, Conway S, Elborn S, Heigerman H . Standards of care for patients with cystic fibrosis: A European Concensus. Journal of cystic fibrosis. 2005; 4: 7-26

Brusasco V, Crapo R, Viegi G. Series “ATS/ERS Task force: Standardisation of lung function testing” General considerations for lung function testing. European Respiratory Journal. 2005; 26: 153-161.

I hope this helps.

Best Wishes

Fiona Kerr
The answer is edited by: Fiona Kerr