A "bad" pulmonary function test score indicates an abnormality in lung function, typically reflected by a lower-than-expected Forced Expiratory Volume in one second (FEV1) percentage of predicted. Generally, an FEV1 percentage of predicted below 70% is considered abnormal, with lower percentages indicating greater severity of impairment.
Understanding FEV1 and Its Significance
The Forced Expiratory Volume in one second (FEV1) is a crucial measurement in pulmonary function tests (PFTs). It represents the amount of air a person can forcibly exhale in the first second after taking a deep breath. This value is then compared to an average predicted value for individuals of similar age, sex, height, and ethnicity to determine a percentage of predicted FEV1. This percentage helps classify the severity of any observed lung function impairment.
Severity Grades for Pulmonary Function Test Abnormality
The severity of a pulmonary function test abnormality, particularly for obstructive patterns (where FEV1 is reduced), is often graded based on the FEV1 percentage of predicted. The lower the percentage, the more severe the lung impairment.
Here's a breakdown of the severity grades:
| Severity | FEV1 Percentage of Predicted |
|---|---|
| Normal | ≥ 70 |
| Mild | > 70 (but within abnormal context if other parameters are off) |
| Moderate | 60 to 69 |
| Moderately Severe | 50 to 59 |
| Severe | 35 to 49 |
| Very Severe | < 35 |
- Mild Abnormality: While an FEV1 percentage of predicted above 70% is often considered within a normal range, a value slightly above 70% might still be indicative of a mild abnormality if other PFT parameters are also compromised or if there's a clinical suspicion of lung disease.
- Moderate to Severe Abnormality: Scores falling into the moderate, moderately severe, and severe categories indicate increasingly significant lung function impairment. For example, an FEV1 of 45% of predicted would be classified as severe.
- Very Severe Abnormality: An FEV1 percentage of predicted below 35% signifies very severe airflow limitation, often associated with significant symptoms and impact on daily life.
These classifications help healthcare professionals understand the extent of lung disease and guide treatment decisions, particularly for conditions like Chronic Obstructive Pulmonary Disease (COPD).
