Asthma Diagnosis and Investigations MCQs
Do the following MCQs on Asthma. Explanations for the answers are available in the text given below.
How to diagnose asthma?
The diagnosis of asthma is based on the clinical features and investigations. The clinical features include cough, wheeze and breathlessness. These symptoms will improve with bronchodilators.
Simultaneously we should think about other differential diagnoses also.
What are the differential diagnoses?
Asthma is characterized by recurrent wheezing. Following are a list of other conditions which can give rise to recurrent wheeze.
- Intra bronchial foreign body
- Recurrent lower respiratory tract infections
- Mediastinal masses
- Heart failure
- Gastro oesophageal reflux
- H-type tracheo oesophageal fistula
- Immune deficiency
- Loeffler syndrome
- Vascular rings
- Cystic fibrosis
- Ciliary dyskinesia
Therefore during history and examination questions should be asked to exclude these conditions.
What are the investigations which will help in the diagnosis of asthma?
The appropriate investigations are lung function tests, chest X ray and hypersensitivity tests. These tests are difficult to perform in children under 5 years. Therefore diagnosis is based on mainly clinical features in young children.
Lung function tests are PEFR and FEV1.
What is PEFR?
PEFR is Peak Expiratory Flow Rate. It is measured by using a peak flow meter. Watch the following video about using a peak flow meter.
PEFR measures the maximum expiratory flow rate. The method of diagnosing asthma using PEFR is given below.
Step 1 – Measure the initial PEFR. (Eg:- Assume that it is 300 L/min.) This value is before the bronchodilator therapy.
Step 2 – Give the bronchodilator. Then measure PEFR again. (Eg:- Assume that it is 400 L/min.)
Step 3 – Take the difference between these two values. (In this case, it is 100 L/min.)
Step 4 – Now calculate the PEFR variability. (Eg:- PEFR variability = (100/400)×100% = 25%)
If PEFR variability is more than 20%, it is highly suggestive of asthma.
What is FEV1?
FEV1 is Forced Expiratory Volume in the first second. This value is taken as the percentage of the predicted value. Normal value of FEV1 should be more than 80%.
In spirometry FVC is also measured simultaneously. FVC is Forced Vital Capacity. It also should be more than 80% of the predicted value.
Then we calculate FEV1/FVC ratio. This should be more than 70% normally. FEV1/FVC value less than 70% means airway obstruction.
In asthma, there is airway obstruction. Therefore FEV1/FVC is less than 70%. The degree of obstruction is determined by FEV1 value.
|FEV1 > 80%||Mild obstruction|
|80% > FEV1 > 50%||Moderate obstruction|
|50% > FEV1 > 30%||Severe obstruction|
|30% > FEV1||Very severe obstruction|
The characteristic feature is the obstruction reverses with bronchodilation. After administration of a bronchodilator FEV1 should increase. That increment should be more than 200 ml or 12%.