General investigations of importance which point to disease of the respiratory organisms include peripheral blood picture, total and differential leukocyte counts and determination of ESR. Lymphocytosis is suggestive of chronic inflammatory disease like tuberculosis whereas neutrophil leukocytosis occurs in acute infections like pneumonia. Increase in eosinophils above 10% calls for estimation of the absolute eosinophil count. Mild and moderate increase in eosinophils is very common in Indian subjects. This is caused by factors such as helminthiasis and external allergens. In susceptible subjects even moderate eosinophils may present with symptoms of respiratory allergy. High eosinophil counts are found in bronchial asthma, hydatid disease and pulmonary eosinophilia. Chronic hypoxemia results in the development of secondary polycythemia. Elevation of ESR is a nonspecific indicator of inflammatory and neoplastic lesions in the lungs. Erythrocyte sedimentation rate is not a reliable parameter for diagnosis, but in the follow up of a chronic disease like tuberculosis, the ESR may be helpful.
Sputum should be examined macroscopically, microscopically after proper staining, and bacteriologically. Total quantity of sputum in 24 hours, color, consistency and other characteristics like odor and presence of blood are of great value in diagnosis. Presence of fungi in mycotic infections, asbestos bodies in asbestosis and motile amoebae in pulmonary amoebiasis can be detected by direct microscopy of fresh sputum. Gram's stain and Ziehl-Neelsen's stain are employed to identify the bacterial pathogens in the smear. Malignant cells can be detected by cytological examination, Wet preparations stained with methylene blue may suggest the presence of malignant cells, some staining help to identify the malignant cells further.
Sputum culture is done to identify the organisms and their sensitivity to various antibiotics. Proper collection of the specimen is essential for getting reliable results. Sputum should be taken directly into sterile receptacles. Contamination by oropharyngeal organisms leads to fallacious results on culture. Uncontaminated specimens of sputum can be obtained by trans-tracheal aspiration. Bronchial washings collected through a bronchoscope or smears collected by a brush during bronchoscopy are ideal specimens for cytological and microbiological studies, where facilities are available.
Plain X-ray chest-posteroanterior (PA) view
Radiographs are taken in full inspiration with the film placed in front of the chest and the source of X-rays kept 1.5-2m behind the patient. In addition to PA views, lateral views are also taken with the affected side close to the film to locate the bronchopulmonary segment which is the seat of disease. In normal skiagrams, the lungs appear as translucent zones in which bronchovascular marks are clearly detectable and can be traced almost to the periphery.
The trachea, mediastinum, costophrenic, and cardiophrinic angles and the level of the diaphragm are taken as landmarks in the interpretation of chest skiagram. On either side the lung fields are compared zone by zone. For purposes of description the lung fields are divided into the upper, middle, and the lower zones. A horizontal line at the level of the lower margin of the anterior end of the second rib separates the upper from middle zone, and a horizontal line passing through the lower margin of the anterior end of the fourth rib separates the middle from the lower zone. Chest radiographs give evidence of morphological lesions. In many instances, radiological appearances help to infer the aetiology as well.