What should you know about spirometry filters?

The filter sits between your mouthpiece and the spirometer. It is intended to trap moisture and particles from exhaled air before they reach internal parts of the equipment. A filter is not a treatment and it does not make a lung function result abnormal or normal by itself. The clinician also uses cleaning, ventilation, and equipment procedures to support infection control.

Use the new or service-approved filter provided for your test and do not share a mouthpiece. Make a close lip seal around it, then follow the instructions for inhaling and forceful exhaling. If the filter feels blocked, damp, loose, or difficult to breathe through, tell the clinician immediately rather than adjusting the equipment yourself. Coughing or saliva may mean the manoeuvre needs to be repeated.

A filter cannot protect you from an acute breathing emergency. Get urgent help for severe breathlessness, fainting, confusion, blue or grey lips, or rapidly worsening wheeze. Tell the testing team before starting if you have a contagious respiratory illness, fever, or a cough that is producing blood, so they can advise on the appointment.

Ask whether the filter is single-use, whether it changes the test procedure, how the equipment is cleaned, and whether coughing or discomfort affected the quality of your result.