For the diagnosis of obstructive airway disease which of the following is preferred
**Core Concept**
Obstructive airway disease, characterized by airflow limitation due to bronchial hyperresponsiveness and airway inflammation, requires a diagnostic approach that assesses the degree of airflow limitation and reversibility. Spirometry, a pulmonary function test, is the gold standard for diagnosing and monitoring obstructive airway diseases.
**Why the Correct Answer is Right**
The preferred diagnostic test for obstructive airway disease is the **Forced Expiratory Volume in 1 second (FEV1)/Forced Vital Capacity (FVC) ratio**. This ratio, calculated from spirometry results, measures the proportion of the vital capacity that can be exhaled in the first second of forced expiration, indicating the degree of airflow limitation. A ratio of less than 0.7 is indicative of obstructive lung disease. The FEV1/FVC ratio is sensitive to changes in lung function and is used to monitor disease progression and response to treatment.
**Why Each Wrong Option is Incorrect**
* **Option A:** Peak expiratory flow rate (PEFR) is a measure of the maximum rate of airflow during forced expiration and is used to monitor asthma control but is not the preferred diagnostic test for obstructive airway disease.
* **Option B:** Chest X-ray is a useful tool for evaluating lung structure and identifying signs of lung disease, but it is not specific for diagnosing obstructive airway disease.
* **Option D:** Body plethysmography is a technique used to measure lung volumes and is useful in diagnosing restrictive lung diseases, but it is not the preferred diagnostic test for obstructive airway disease.
**Clinical Pearl / High-Yield Fact**
When interpreting spirometry results, remember that a **FEV1/FVC ratio of less than 0.7** is indicative of obstructive lung disease, and a 12% or greater increase in FEV1 after bronchodilator administration is suggestive of reversibility.
**Correct Answer:** C.