If theFEV1/FVC ratio is <80%, it indicates that an obstructive defect is present.
Asthma is defined as a reversible obstructive defect. Therefore, a patient with an FEV1/FVC ratio < 80% can be given a bronchodilator (i.e. albuterol) and the spirometry can be repeated. If the FEV1 increases by more than 12%, it is indicative of reversible airway disease. If the FEV1 does not increase by more than 12%, it is considered nonreversible or fixed airway disease(i.e. COPD). Because asthma is a reversible obstructive defect, the spirometry may be normal at the time of evaluation. In instances where asthma is strongly considered yet the spirometry is normal, a methacholine challenge may be needed. In this test, a patient inhales one or more concentrations of methacholine, and results of spirometry before and after the inhalations are measured. The amount of methacholine needed to elicit a drop of 20% in the FEV1 (known as the PD20) is obtained. The lower the PD20, the more likely that the patient has reactive airways. The reader is directed elsewhere for a more complete review of methacholine testing.
Source: https://www.med.umich.edu/intmed/allergy/edu/syllabus/TOPICS/PFTs/fig5.htm
Figure 5 - Quick interpretation of spirometry
Asthma is defined as a reversible obstructive defect. Therefore, a patient with an FEV1/FVC ratio < 80% can be given a bronchodilator (i.e. albuterol) and the spirometry can be repeated. If the FEV1 increases by more than 12%, it is indicative of reversible airway disease. If the FEV1 does not increase by more than 12%, it is considered nonreversible or fixed airway disease(i.e. COPD). Because asthma is a reversible obstructive defect, the spirometry may be normal at the time of evaluation. In instances where asthma is strongly considered yet the spirometry is normal, a methacholine challenge may be needed. In this test, a patient inhales one or more concentrations of methacholine, and results of spirometry before and after the inhalations are measured. The amount of methacholine needed to elicit a drop of 20% in the FEV1 (known as the PD20) is obtained. The lower the PD20, the more likely that the patient has reactive airways. The reader is directed elsewhere for a more complete review of methacholine testing.
Source: https://www.med.umich.edu/intmed/allergy/edu/syllabus/TOPICS/PFTs/fig5.htm
Figure 5 - Quick interpretation of spirometry
- Are the patient's age, weight, and height correct?
- Is the effort acceptable? (based on lab technician comments and adequate volume time curve)
- Is an obstructive defect present (FEV1/FVC < 80%)
- If an obstructive defect is present, how severe is it
- FEV1 > 80% predicted = minimal
- FEV1 65 – 80% predicted = mild
- FEV1 50 - 65% predicted = moderate
- FEV1 < 50% = severe
- Does the shape of the curve suggest where the obstruction might be? (variable intrathroacic/extrathoracic, fixed)
- Is an early obstructive defect of the small airways present? (FEF 25-75 < 60%)
- Is a restrictive defect suggested? (FVC < 80% predicted
The FEV1/FVC ratio, also called Tiffeneau-Pinelli index,[1] is a calculated ratio used in the diagnosis of obstructive and restrictive lung disease.[2][3] It represents the proportion of a person's vital capacity that they are able to expire in the first second of forced expiration.[4]
Normal values are approximately 80%.[5] Predicted normal values can be calculated online and depend on age, sex, height, mass and ethnicity as well as the research study that they are based upon.
A derived value of FEV1% is FEV1% predicted, which is defined as FEV1% of the patient divided by the average FEV1% in the population for any person of similar age, sex and body composition.
Normal values are approximately 80%.[5] Predicted normal values can be calculated online and depend on age, sex, height, mass and ethnicity as well as the research study that they are based upon.
A derived value of FEV1% is FEV1% predicted, which is defined as FEV1% of the patient divided by the average FEV1% in the population for any person of similar age, sex and body composition.
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