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SaO₂ of 85%. An oxygen saturation of 85% indicates significant hypoxemia and impaired gas exchange. This finding reflects ventilation–perfusion mismatch rather than structural hyperinflation of the lungs. Although severe asthma can cause hypoxemia, oxygen saturation alone does not specifically demonstrate air trapping or hyperinflation.

PEF rate of <150 L/min. A markedly reduced peak expiratory flow rate indicates severe airway obstruction and limited expiratory airflow. This measurement reflects bronchoconstriction severity but does not directly identify air trapping or lung hyperinflation. PEF assesses airflow limitation rather than changes in lung volumes or thoracic structure.

FEV₁ of 85% of predicted. An FEV₁ at 85% of predicted is within normal or near-normal limits for lung function. This value suggests minimal airflow obstruction rather than severe bronchoconstriction. Such a result would not be consistent with air trapping or hyperinflation.

Clubbing of fingers. Clubbing is associated with chronic hypoxemia seen in conditions such as lung cancer, cystic fibrosis, or interstitial lung disease. Asthma is typically a reversible airway disease and does not cause long-standing hypoxia severe enough to produce digital clubbing. The presence of clubbing would suggest an alternative chronic pulmonary pathology.

Productive cough with green sputum. Green or purulent sputum suggests bacterial infection, such as pneumonia or bronchitis. Asthma exacerbations are usually associated with nonproductive cough or minimal clear sputum due to mucus hypersecretion. Purulent sputum does not support asthma as the primary diagnosis.

Hemoptysis. Hemoptysis indicates bleeding within the respiratory tract and is commonly associated with infections, pulmonary embolism, tuberculosis, or malignancy. Asthma does not typically cause airway bleeding or blood-tinged sputum. This finding would warrant evaluation for other serious pulmonary conditions.

Presence of a bacterial respiratory infection. Bacterial infections cause airway inflammation and purulent secretions but do not produce immediate bronchoconstriction in response to methacholine. The methacholine test does not assess infectious processes or identify pathogens. A positive result reflects airway reactivity rather than infection.

Chronic obstructive pulmonary disease. COPD is characterized by fixed or poorly reversible airflow limitation due to emphysematous or chronic bronchitic changes. Patients with COPD typically have a less pronounced response to methacholine compared with those who have asthma. The test is not used to diagnose COPD and does not confirm irreversible airway obstruction.

Pulmonary embolism. Pulmonary embolism affects pulmonary perfusion rather than airway smooth muscle tone. Methacholine does not provoke vascular obstruction or clot formation. Diagnostic testing for pulmonary embolism relies on imaging and laboratory studies, not bronchoprovocation.

FEV₁ remains unchanged after bronchodilator therapy. Lack of improvement in FEV₁ suggests fixed airflow obstruction rather than reversible disease. This pattern is more consistent with chronic obstructive pulmonary disease or advanced airway remodeling. Absence of reversibility does not support a diagnosis of asthma.

FVC is significantly decreased, with no change after bronchodilator. A reduced forced vital capacity without bronchodilator response suggests restrictive lung disease or severe air trapping. Restrictive disorders involve reduced lung compliance rather than bronchial smooth muscle constriction. This pattern does not reflect the reversible obstruction characteristic of asthma.

Total lung capacity is reduced. Reduced total lung capacity indicates restrictive lung pathology such as pulmonary fibrosis or neuromuscular disease. Asthma typically presents with normal or increased total lung capacity due to air trapping. A decreased TLC is inconsistent with asthma pathophysiology.

Mild, well-controlled asthma. Mild or well-controlled asthma typically presents with normal breath sounds between exacerbations. Airflow is adequate, and wheezing may be absent. Diminished breath sounds are inconsistent with effective asthma control.

Early recovery from an exacerbation. Recovery from an asthma exacerbation is associated with improving airflow and resolution of bronchoconstriction. Breath sounds generally become clearer as wheezing decreases and air movement improves. Diminished breath sounds suggest worsening rather than improvement.

Pulmonary embolism. Pulmonary embolism primarily affects pulmonary perfusion rather than airway caliber. Breath sounds in pulmonary embolism are often normal unless complications such as pleural effusion occur. This condition does not explain diffuse diminished breath sounds with wheezing.