From the Guidelines
A normal Pulmonary Function Test (PFT) value, also referred to as PETH in this context, is typically assessed as % predicted forced expiratory volume in 1 s (FEV1), with normal ranges based on weight-for-age/length-for-age in children < 2 years old or optimal BMI in older children and adolescents. It's essential to note that the term "PETH" is not standard in the context of pulmonary function tests, and it seems there might be a confusion with the term used in the question. However, focusing on pulmonary function tests, the key parameters include FEV1, Forced Vital Capacity (FVC), and the FEV1/FVC ratio, among others.
Key Parameters for Normal PFT Values:
- FEV1: The volume exhaled in one second, expressed as a percentage of the predicted normal value based on age, sex, height, and ethnicity.
- FVC: The total volume of air exhaled from the lungs after maximal inhalation, also expressed as a percentage of the predicted normal value.
- FEV1/FVC Ratio: This ratio helps in diagnosing obstructive and restrictive lung diseases.
According to the provided evidence, particularly from 1, pulmonary function is assessed as % predicted forced expiratory volume in 1 s (FEV1), with normal ranges determined by factors such as weight-for-age/length-for-age in young children or optimal BMI in older children and adolescents.
Interpretation of PFT Results:
- Normal: FEV1 and FVC are within 80% of the predicted value, and the FEV1/FVC ratio is above 70% for adults.
- Obstructive Pattern: Reduced FEV1/FVC ratio, indicating diseases like asthma or COPD.
- Restrictive Pattern: Reduced FVC with a normal or increased FEV1/FVC ratio, suggesting conditions like pulmonary fibrosis.
Given the information and focusing on the most recent and highest quality study relevant to the question, the assessment of normal pulmonary function is highly individualized and depends on various factors including age, sex, height, and ethnicity 1. Therefore, it's crucial to consult specific reference values for each parameter based on these factors for accurate interpretation.
From the Research
Normal PETH Values
The normal values for Pulmonary Function Tests (PFTs), including PETH, can vary depending on several factors such as age, gender, ethnicity, and body size.
- According to 2, lung function parameters vary considerably with age and body size, and the normal range of expected values must be individualized.
- For spirometry, the lower limit of normal (LLN) is taken to be equal to the 5th percentile of a healthy, non-smoking population.
- A more accurate LLN for the FEV(1)/FVC ratio can be determined by subtracting 10 (10% or 0.10) from the age-specific FEV(1)/FVC predicted for any individual.
Interpretation of PETH Results
The interpretation of PETH results can be complex, and minor variations in test results can cause unwarranted worry to patients.
- As stated in 3, the usual process for establishing "normal values/reference ranges" entails testing at least 120 healthy individuals in a given age-group, gender, ethnicity, testing method, and related health issues.
- The central 95% of the values is usually adopted as the normal range, which means that 5% of healthy individuals may be labeled as having abnormal laboratory results.
- It is essential to consider the clinical significance of the findings and report normal values along with patient results, including information on whether the results warrant discussion with a doctor or further action 3.
Factors Affecting PETH Results
Several factors can affect PETH results, including age, gender, ethnicity, and testing methods.
- As mentioned in 2, simple "rules of thumb" such as an FEV(1)/FVC < 0.70 to indicate air-flow obstruction or assuming values < 80% of predicted to be abnormal are inaccurate and can cause misclassification.
- The analysis and mathematical descriptions of reference data have become increasingly sophisticated, but the interpretation of values near the LLN continues to carry uncertainty due to an overlap in values between low normal values and those reflecting early disease 2.