The accuracy of peak flow monitoring depends on your effort during the test. Results will be inaccurate if you do not follow directions or do not give your best effort during testing. The following factors also may affect the results of peak flow monitoring:
Using medicine that expands the airways in the lungs within 4 hours before the test may improve test results.
Using sedatives before the test may worsen test results.
People who have pain while breathing may not be able to breathe normally. So the results of their tests may be misleading.
What To Think About
Your doctor may do a complete series of lung function tests to confirm a lung disease, monitor the progression of lung disease, or monitor the effectiveness of treatment. To learn more, see the topic Lung Function Tests.
When using a home peak flow meter, it is best to use the same meter over time. Different brands of meters give different results. If you change your peak flow meter, you need to redetermine your personal best measurement using the new machine.
Wash your meter according to the manufacturer's directions to prevent growth of bacteria and fungi.
PEF is lowest in the early morning and highest in the afternoon. If you measure your PEF only once a day, do so first thing in the morning before using any bronchodilator medicine.
People with intermittent or mild persistent asthma may not need to check their PEF every day. But if symptoms develop, checking peak expiratory flow often for a period of time may be helpful in bringing asthma under control.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Holcroft CA, et al. (2003). Measurement characteristics of peak expiratory flow. Chest, 124(2): 501-510.
National Institutes of Health (2007). National Asthma Education and Prevention Program Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma (NIH Publication No. 08-5846). Available online: http://www.nhlbi.nih.gov/guidelines/asthma/index.htm.