In chronic bronchitis, the pathological hallmark is an increase in the ratio of mucous gland layer thickness to bronchial wall thickness. What is the name of this ratio?

Explanation

## Reid Index: The Pathological Hallmark of Chronic Bronchitis **Key Point:** The **Reid index** is the ratio of the thickness of the mucous gland layer to the total thickness of the bronchial wall. A Reid index **>0.5** is diagnostic of chronic bronchitis. ### Definition and Calculation $$\text{Reid Index} = \frac{\text{Thickness of mucous gland layer}}{\text{Total thickness of bronchial wall}}$$ - **Normal value:** <0.4 (or <0.5 depending on source) - **Chronic bronchitis:** >0.5 - This increase reflects **hypertrophy and hyperplasia** of mucous glands in the bronchial wall ### Pathophysiological Basis **High-Yield:** Chronic irritation from cigarette smoke and air pollutants stimulates: 1. Hypertrophy of existing mucous glands 2. Hyperplasia of mucous cells 3. Increased mucus production 4. Goblet cell metaplasia in small airways This leads to the characteristic productive cough and airway obstruction in chronic bronchitis. ### Clinical Significance **Clinical Pearl:** The Reid index is a **microscopic/histopathological finding** used in autopsy studies and research. It is not measured clinically but helps pathologists confirm the diagnosis of chronic bronchitis at necropsy. ### Distinction from Other Indices | Index/Ratio | Definition | Use | |-------------|-----------|-----| | **Reid index** | Mucous gland thickness / Bronchial wall thickness | Pathological diagnosis of chronic bronchitis | | **Tiffeneau index** | FEV1/FVC ratio | Clinical assessment of airflow obstruction | | **FEV1/FVC ratio** | Forced expiratory volume in 1 sec / FVC | Diagnostic criterion for COPD (spirometry) | | **Brinkman index** | Cigarettes per day × years smoked | Quantification of smoking exposure | [cite:Robbins 10e Ch 15]