Many times asthma is not properly diagnosed and treated. It is because proper investigations are not done.

Tests for diagnosis

  • Spirometry (Lung Function Test / Pulmonary Function Test) is carried out with the aid of computerized machines. It is an objective method to confirm the diagnosis. The patients blows into a tube, the results of which are analyzed on a computer. This is done to confirm the presence of asthma and to asses its severity. It can be useful also in estimating the improvement following treatment. These tests should be repeated at a regular intervals for the purpose of monitoring the condition of the patient. The important parameters assessed include Forced Expiratory Volume in one second (FEV1), Forced Vital Capacity (FVC) and Peak Expiratory Flow Rate (PEFR).

Tests for diagnosis by exclusion

  • Chest X-Ray is not of much importance in diagnosing asthma but is important in ruling out other causes of cough, breathlessness and lung infections (e.g. pneumonia, fungal diseases and tuberculosis).
  • Sputum smear and culture – It can be done in some patients to detect acute infections of the lung (e.g. pneumonia, fungal diseases and tuberculosis).
  • Diffusing capacity of carbon monoxide (DLco): This test helps distinguish between smokers with asthma from smokers with chronic bronchitis (COPD). The values remain unchanged in asthma as against COPD in which DLco usually decreases.

Test for monitoring

  • Mini Peak Flow Meter (PEFR)This is a small, simple and portable instrument which can be used by the patient at his/her house. The patient blows into the instrument (Peak Flow Meter) and it gives an indication of the patient’s lung function (i.e. PEFR – Peak Expiratory Flow Rate). It can be useful in
    • Assessing patient’s daily condition (monitoring)
    • As a warning to the patient (impending attack).
    • To check for the effect of the medicines given.


Other corroborative tests

  • C.T. Scan done at High Resolution (HRCT) gives excellent details of lung’s anatomy for characterizing emphysema (COPD) and thus aids in distinguishing asthma from emphysema (COPD).
  • IgE levels – In some asthma patients the levels of IgE in blood have been found to be unusually high.
  • Blood tests – Total Leukocytic Count (TLC), Differential Leukocytic Count (DLC) and Eosinophilic Count to detect Eosinophilia can be done.
  • Exercise test – This test can be done to detect mild asthma or asthma in children.
  • Allergy test – This test is to look for the trigger factors causing asthma. It can also diagnose the cause of occupational asthma. Allergy test is generally useful in  diagnosing seasonal asthma by detecting the triggers causing the attack.
  • Tests done in severe asthma
  • Pulse Oximetry – It is usually done in a severe attack of asthma to check the oxygenation saturation (level of oxygen in the blood) of the patient.
  • Arterial Blood Gases (ABG) – It is also done in a severe attack of asthma in order to treat the patient with oxygen and mechanical ventilation in the Intensive Care Unit (ICU). It gives various parameters like level of oxygen, carbon dioxide and pH in the blood of the patient.