Investigations are required for exclusion of an alternate diagnosis, confirmation of diagnosis of COPD, assessment of severity of disease and diagnosis of complications.

Excluding alternate diagnosis

It is especially important to exclude tuberculosis in all patients having chronic cough. Examine sputum smears for acid-fast bacilli (AFB), at least thrice.

Chest radiograph will help to identify alternate diseases such as fibrocavitary tuberculosis, bronchiectasis, lung tumours and detect complications such as chronic cor pulmonale, pneumothorax or bronchopneumonia.

Additional tests such as the spirometry may be carried out where physician feels the diagnosis of asthma is under consideration. Bronchodilator reversibility testing is useful to help rule out a diagnosis of asthma and to establish patient’s best attainable lung function. PEFR with reversibility may be substituted for FEV₁ when spirometry is not available.

In situation when patient is not responding to adequate and properly prescribed therapy or if there is a doubt of an alternate diagnosis such as asthma, glucocorticoid reversibility test with 2 week of oral corticosteroids should be attempted (by a specialist at the secondary care center with facilities for spirometry).³⁷ Criteria for reversibility are an increase in FEV₁ of 200 ml and 15% above baseline.

Confirming the diagnosis

Spirometry remains the gold standard for confirmation and staging of COPD. Patients should be referred for spirometry if diagnosis is doubtful. Spirometry is used to measure the forced vital capacity (FVC), i.e. maximal volume of air forcibly exhaled from the point of maximal inhalation; the volume of air exhaled during the first second of this maneuver (FEV₁), and the ratio of these two measurements (FEV1/FVC). The presence of a postbronchodilator FEV₁<80% of the predicted value in combination with a FEV₁/FVC <70% confirms the presence of airflow limitation that is not fully reversible. Predicted values of different spirometric parameters are available as normograms and tables drawn from different prediction equations.

Staging severity of COPD

Assessment of severity is based on the degree of the spirometric abnormality. Based on the results of spirometry, COPD can be categorized into four stages: At risk, Mild, Moderate and Severe (Table 2). If spirometry is not available, both staging of the disease and follow up of patients should be done on the basis of severity of symptoms / level of disability / 6 minute walk test and/or peak expiratory flow (PEF) (Table 3).^38-40

Although spirometry is the gold standard for staging, PEF can serve as a good substitute if spirometry is not available. Six minute walking test is performed by measuring distance covered in 6 minutes when patient walks at his/her own speed (under physician supervision). This is a simple test, which can be performed at the primary care level. Measurement of arterial blood gases / pulse oximetry in patients with severe COPD is desirable although severity of respiratory failure may be assessed by symptoms of hypercapnia (bounding pulse, warm extremities, flaps and tremulousness) and hypoxia (tremors, restlessness, mental obtundation and cyanosis.