Routine haematological and biochemical tests
These should include tests for:
• Haemoglobin, to detect the presence of anaemia
• Packed cell volume (rev) (secondary polycythaernia occurs with chronic bronchitis and emphysema)
• Routine biochemistry
Other blood investigations sometimes required include ai-antitrypsin levels, autoantibodies, and, in asthma, IgE to specific allergens (RAST; radioallergosorbent test) and Aspergillus antibodies.
Sputum should be inspected for colour:
• Yellow-green indicates inflammation (infection or allergy)
• Presence of blood suggests neoplasm or pulmonary infarct
Microbiological studies (Gram stain and culture) are not helpful in upper respiratory tract infections or in acute or chronic bronchitis. They are of value in:
• Diagnosis of tuberculosis (Ziehl-Nielsen stain)
• Unusual clinical problems
• Aspergillus lung disease
This is extremely useful in the diagnosis of bronchial carcinoma. Advantages are:
• Quick result
However, its value depends on the production of sputum and the presence of a reliable cytologist. Sputum can be induced following the inhalation of nebulized hypertonic saline (5%). This is unpleasant and for important samples it is better to proceed to transtracheal aspiration or more usually bronchoscopy and bronchial washings.
This technique involves pushing a needle through the cricothyroid membrane, through which a catheter is threaded to a position just above the carina. This procedure induces coughing, and specimens are collected by aspiration or by the introduction and subsequent aspiration of sterile saline. It is an excellent technique (although not often required) for assessing infection in the lower respiratory tract because it obviates any possibility of contamination of the specimen with bacteria from the pharynx and mouth.
Chest X-ray The following must be taken into account when viewing films:
CENTRING OF THE FILM. The distance between each clavicular head and the spinal processes must be equal.
THE VIEW. Postero-anterior (PA) is the routine film. Antero-posterior (AP) films are only taken in very ill patients who are unable to stand up or be taken to the radiology department; the cardiac outline appears bigger and the scapulae cannot be moved out of the way.
The following should be noted:
• The shape and body structure of the chest wall
• Whether the trachea is central
• Whether the diaphragm is elevated or flat
• The shape, size and position of the heart
• The shape and size of the hilar shadows
• The vascular shadowing and the size and shape of any abnormalities of the lungs.
COLLAPSE AND CONSOLIDATION. A diagram showing the X-ray changes in collapse of a whole lung is given. In collapse of the middle lobe, all that may be detected is a loss of the clear outline of the right atrium, which distinguishes it from collapse of the right lower lobe. In consolidation, the segments or lobes of the lung are opaque but the bronchi are patent, producing an air bronchogram. Causes of collapse are shown.
PLEURAL EFFUSION. Pleural effusions need to be more than 500 m1 to cause much more than blunting of the costophrenic angle. On an erect film they produce a characteristic shadow with a curved upper edge rising into the axilla. If very large, the whole of one side of the thorax may be opaque, with shift of the mediastinum to the opposite side.
FIBROSIS. Localized fibrosis causes streaky shadowing and the accompanying loss of lung volume causes mediastinal structures to move to the same side. More generalized fibrosis in the lung can lead to a honeycomb appearance, seen as diffuse shadows containing multiple circular translucences a few millimetres in diameter.
ROUND SHADOWS. The causes of round shadows are shown.
MILIARY MOTTLING. This term describes numerous minute opacities, 1-3 mm in size, which are caused by many pathological processes. The commoner causes are miliary tuberculosis, pneumoconiosis, sarcoidosis, fibrosing alveolitis and pulmonary oedema, though the latter is usually perihilar and accompanied by larger, fluffy shadows. A rare but striking cause of miliary mottling is pulmonary microlithiasis.