Asthma Diagnosis: Lung Function Tests, Blood tests and Imaging

It is generally not difficult to differentiate asthma from other conditions that cause wheezing and wheezing. Upper airway obstruction by a tumor or laryngeal edema can simulate severe asthma, but patients often have stridor located in the large airways. Diagnosis is confirmed by a flow-volume circuit showing a reduction in inspiratory and expiratory flow and bronchoscopy to demonstrate the site of upper airway narrowing. Persistent wheezing in a specific area of ​​the chest may indicate an endobronchial obstruction with a foreign body. Left ventricular failure can simulate wheezing in asthma, but there are basal crunches in contrast to asthma. Vocal cord dysfunction can simulate asthma and is believed to be a hysterical conversion syndrome

Eosinophilic pneumonia and systemic vasculitis, including ChurgStrauss syndrome (eosinophilic granulomatosis with polyangiitis) and knotty polyartheritis, can be associated with wheezing. Chronic obstructive pulmonary disease (COPD) is usually easy to differentiate from asthma as symptoms show less variability, never fully attenuate and show much less (or absent) reversibility to bronchodilators. About 15% of patients with COPD have asthma characteristics, with an increase in eosinophils in the sputum and a response to OCS; these patients probably have both diseases simultaneously

Asthma Diagnosis

There is no specific or single test that can diagnose asthma. Diagnosis is mainly based on a good medical history of the patient,  may have a family history of allergy or asthma or have symptoms of allergic rhinitis. The diagnosis of asthma is usually evident from symptoms of variable and intermittent airway obstruction, but must be confirmed by objective measurements of lung function

Physical Examination 

In patients with asthma is usually completely normal. That said, you should listen for wheezing on lung examination and sounds from the upper airways (stridor) because this large airway obstruction can sometimes mimic asthma

• Have you had a sudden severe episode or recurring episodes of coughing, wheezing (sharp wheezing)?

• Having trouble breathing?

• Have you had colds that affected your chest or more than 10 days have passed to recover?

• Have you had a cough, wheezing, or difficulty breathing during a particular season or time of year?

• Have you had a cough, wheezing or difficulty breathing in certain places or when you have been exposed to certain things (eg, animals, tobacco smoke, perfumes)?

• Are symptoms relieved when using medications? You have had a cough, wheezing or shortness of breath in the past 4 weeks 

•   Who woke you up at night?
•    Early in the morning?
•   After a run, moderate exercise or other physical activity?

Lung Function Tests

Simple spirometry confirms airflow limitation with a reduction in FEV1, FEV1 / FVC and PEF ratios. Reversibility is demonstrated by a> 12% 200 mL increase in FEV1 15 min after a short-acting inhaled β2 agonist (SABA; such as inhaled albuterol 400 μg) or in some patients from a 2-4 week study with corticosteroids. oral (OCS) (prednisone or prednisolone 30 to 40 mg per day). Twice-daily PEF measurements can confirm diurnal variations in airflow obstruction

Airway Responsiveness

Although there is no single diagnostic test for asthma, bronchodilator reactive spirometry is a common next step in evaluation. Most patients with asthma will have normal lung function when they don't have an exacerbation, so this finding does not rule out the diagnosis. If the patient is symptomatic, spirometry should show an obstructive pattern with forced expiratory volume (FEV1) / forced vital capacity (FVC) of 70%. If FEV1 or FVC improves with the use of a bronchodilator, this would support the diagnosis of asthma because part of the definition of the disease is the reversibility of airflow obstruction

Laboratory Tests

Blood tests are often not helpful

• In some patients it is possible to measure total serum IgE and specific IgE against inhaled allergens (radioallergic absorption test [RAST])

• High FeNO (greater than 12 ppb)

Fractionated exhaled nitric oxide (FENO) is now being used as a non-invasive test to measure eosinophilic inflammation of the airways. ICS reduces typically elevated levels in asthma, so this can be evidence of adherence to therapy

• Positive methacholine provocation test (PC20 FEV1 less than 12.5 mg / mL)

The pulmonologist may perform a test called a methacholine challenge, administering the drug methacholine to see if it initiates a mild hypersensitivity reaction. A positive response (symptoms appear) is quite conclusive of an asthma diagnosis

• Skin tests are not useful for diagnosis. Positive skin responses can be helpful in persuading patients to take steps to avoid allergens, which are positive in allergic asthma and negative in intrinsic asthma

Imaging

Chest x-rays are usually normal but may show hyperinflationary lungs in severe patients. In exacerbations, there may be evidence of pneumothorax. Pulmonary shading often indicates pneumonia or eosinophilic infiltrates in patients with bronchopulmonary aspergillosis (BPA). High-resolution CT may display areas of bronchiectasis in patients with severe asthma condition and there may be thickening of the bronchial walls, but these changes are not diagnostic of asthma

Considerations in the Differential Diagnosis of Asthmatic Adults:

It is important to remember that although many of these pathological processes can simulate asthma, they (or their treatments) can also coexist and contribute to the severity of asthma

• Cardiovascular system: coronary heart disease, heart failure, valve disease, pulmonary hypertension, pulmonary embolism

• Infectious: pneumonia, especially atypical organisms, acute bronchitis

• Neoplastic: lung cancer, carcinoid

• Other lung diseases: chronic obstructive pulmonary disease, ABPA, idiopathic pulmonary fibrosis, bronchiectasis, pulmonary eosinophilia, cystic fibrosis, pulmonary manifestations of connective tissue diseases, hypersensitivity pneumonia, sarcoidosis, asbestosis

• Gastroesophageal: gastroesophageal reflux disease (GERD)

• Hematological: anemia, systemic mastocytosis

• General: deconditioning, obesity

• Psychiatric: anxiety, dysfunction of the vocal cords