Investigation of Asthma
Why we investigate asthma patients?
- For classification and assessment of severity
- For diagnosis of concomitant illness
- For exclusion of other causes of cough, wheeze dyspnoea or chest tightness
What are the investigations for asthma?
We should do four basic investigations of all patients.
1. Blood for TC, DC, ESR,
Hb% and :
To exclude Tropical
Eosinophil (TCE) (where eosinophil count > 20%).
2. Sputum for AFB and
To exclude Pulmonary
tuberculosis & for the diagnostic evidence of Pulmonary eosinophilia/Asthma.
|3. Chest X-ray P/A view :||
To exclude Pulmonary
tuberculosis, Consolidation, Pneumothorax, Pulmonary oedema, Tumor, FB in
4. Pulmonary Function
Tests (P.F.T) :
Spirometric analysis to
differentiate obstructive from restrictive disorders and asthma from COPD.
After 40 years of age or in suspected cases we should also advise:
5. Blood glucose to exclude Diabetes mellitus.
6. ECG/Echocardiography to exclude cardiac diseases.
CFT/IFAT for filaria is suggestive but not confirmatory for the diagnosis of tropical pulmonary eosinophilia.
What other concomitant illnesses of an asthma patient should be investigated?
The following problems, which may be present in association with asthma, should be investigated properly.
- Atopic dermatitis (Eczema)
- Allergic rhinoconjunctivitis
- Chronic bronchitis or COPD
- Diabetes mellitus
- Ischemic Heart Disease (IHD)
Spirometry is a method of assessing lung function by measuring the volume of air that the patient is able to expel from the lungs after a maximal inspiration. It is a reliable method of differentiating between obstructive airway disorders (e.g. COPD, Asthma) and restrictive diseases (e.g. ILD). Spirometry can also be used to determine the severity of COPD. This is important because the severity of COPD can not be predicted simply from the clinical signs and symptoms.
Spirometry gives 3 important measures:
FEV1: The volume of air that the patient is able to exhale in the first-second of forced expiration.
FVC: The total volume of air that the patient can forcibly exhale in one breath.
FEV1/FVC: The ratio of FEV1 to FVC expressed as a percentage.
Values of FEV1 and FVC are expressed as a percentage of predicted normal for a person of the same sex, age and height.
Slowly progressive respiratory symptoms in a middle aged and elderly smoker are likely to indicate COPD. However, such patients may also have asthma. Patients whose symptoms started before the age of 40 years are more likely to be asthmatic, particularly if they are non-smokers with symptoms that vary in severity. Serial peak flow monitoring, looking for diurnal variation of greater than 20%, may help to differentiate these conditions.
Alternatively bronchodilator reversibility tests can be used. A change in FEV1, that is, both a >12% increase and >200 ml over pre-bronchodilator levels indicates positive reversibility test. COPD patients with smaller changes are likely to benefit from bronchodilator therapy symptomatically.
Spirometry indicates the presence of an abnormality if any of the following are recorded:
- FEV1Obstructive disorder shows :
- FEV1 reduced (Restrictive disorder shows:
- FEV1 reduced (<80% of predicted value)
- FVC reduced (<80% of predicted value)
- FEV1/FVC ratio normal (>70%)
Broncho- Provocation test:
Fall of FEV1 >20% after inhalation of methacholine or hypertonic saline is used for diagnosis of hyper-responsiveness of airways in susceptible patients with normal spirometry. Susceptible patients are: (i) Patient with cough variant asthma, (ii) Mild intermittent asthma, (iii) Chronic Bronchitis.
Exercise Challenge test:
Fall of FEV1 or PEFR >15% after vigorous exercise indicates Exercise Induced Asthma. The fall starts at 5 to 10 minutes after exercise and peaks at 20 to 30 minutes and then resolves.
- Asthma and Allergy Foundation of America: http://www.aafa.org/
- American Asthma Foundation: http://www.americanasthmafoundation.org/
- Asthma, UK: http://www.asthma.org.uk/all_about_asthma/index.html
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