C5. Specialist referral

Confirmation of the diagnosis of COPD and differentiation from chronic asthma, other airway diseases or occupational exposures that may cause airway narrowing or hyper-responsiveness, or both, often requires specialised knowledge and investigations. Indications for which consultation with a respiratory medicine specialist is recommended are shown in Box 8.

C5.1 Complex lung function tests

Measurement of airways resistance, static lung volumes and diffusing capacity of lungs for carbon monoxide assists in the assessment of patients with more complex respiratory disorders. Inspiratory capacity (IC) indicates the degree of hyperinflation, which relates to a patient’s level of dyspnoea and their exercise tolerance, and is a better predictor of mortality than spirometry. It is therefore finding increased utility for assessing people with COPD as well as response to therapy in clinical research. More specialised measures, including forced oscillometry, have not yet found clinical application despite their relative ease of use.

C5.2 Exercise testing

Cardiopulmonary exercise tests may be useful to differentiate between breathlessness resulting from cardiac or respiratory disease, and may help to identify other causes of exercise limitation (eg, hyperventilation, musculoskeletal disorder). Exercise prescription and monitoring of outcomes from drug or rehabilitation therapies are additional uses for these tests. Walking tests (6-minute walking distance and shuttle tests) are also useful, and can indicate whether exercise oxygen desaturation is occurring.

C5.3 Sleep studies

Specialist referral is recommended for COPD patients suspected of having a coexistent sleep disorder or with hypercapnia or pulmonary hypertension in the absence of daytime hypoxaemia, right heart failure or polycythaemia. Overnight pulse oximetry may be used to assess a need for overnight domiciliary oxygen therapy, and may be indicated in patients receiving long-term domiciliary oxygen therapy to assess whether hypoxaemia has been adequately corrected.

C5.4 Chest x-rays

A plain posteroanterior and lateral chest x-ray helps to exclude other conditions such as lung cancer. The chest x-ray is not sensitive in the diagnosis of COPD, and will not exclude a small carcinoma (< 1cm).

C5.5 High resolution computed tomography

High resolution computed tomography (HRCT) scanning gives precise images of the lung parenchyma and mediastinal structures. The presence of emphysema and the size and number of bullae can be determined. This is necessary if bullectomy or lung reduction surgery is being contemplated. HRCT is also appropriate for detecting bronchiectasis. Vertical reconstructions can provide a virtual bronchogram. Helical computed tomography (CT) scans with intravenous contrast should be used in other circumstances, such as for investigating and staging lung cancer. CT pulmonary angiograms are useful for investigating possible pulmonary embolism, especially when the chest x-ray is abnormal.

C5.6 Ventilation and perfusion scans

The ventilation and perfusion (V/Q) scan may be difficult to interpret in COPD patients, because regional lung ventilation may be compromised leading to matched defects. If pulmonary emboli are suspected, a CT pulmonary angiogram may be more useful. Quantitative regional V/Q scans are helpful in assessing whether patients are suitable for lung resection and lung volume reduction surgery.

C5.7 Transcutaneous oxygen saturation

Oximeters have an accuracy of plus or minus 2%, which is satisfactory for routine clinical purposes. They are more useful for monitoring trends than in single measurements. Oximetry does not provide any information about carbon dioxide status and is inaccurate in the presence of poor peripheral circulation (eg, cold extremities, cardiac failure).

C5.8 Arterial blood gas measurement

Arterial blood gas analysis should be considered in all patients with severe disease, those being considered for domiciliary oxygen therapy (eg, whose FEV₁ is < 40% predicted or < 1 L, whose oxygen saturation as measured by pulse oximetry [SpO₂ ] is < 92%), those with pulmonary hypertension, and those with breathlessness out of proportion to their clinical status). Respiratory failure is defined as a PaO₂ < 60 mmHg (8 kPa) or PaCO₂ > 50 mmHg (6.7 kPa). The latter is termed ‘ventilatory failure’ and is accompanied by either compensated (chronic) or uncompensated (acute) acidosis. Acute respiratory acidosis indicates a need for assisted ventilation.

C5.9 Sputum examination

Routine sputum culture in clinically stable patients with COPD is unhelpful and unnecessary. Sputum culture is recommended when an infection is not responding to antibiotic therapy or when a resistant organism is suspected.

C5.10 Haematology and biochemistry

Polycythaemia should be confirmed as being secondary to COPD by blood gas measurement that demonstrates hypoxaemia. The possibility of sleep apnoea or hypoventilation should be considered if polycythaemia is present but oxygen desaturation or hypoxaemia on arterial blood gas tests are absent when the patient is awake. Hyperthyroidism and acidosis are associated with breathlessness. Hyperventilation states are associated with respiratory alkalosis. Hypothyroidism aggravates obstructive sleep apnoea.

The prevalence of severe homozygous (ZZ) alpha1 antitrypsin deficiency has been estimated at between 1/4,348 and 1/5,139 in European populations³⁴. Although 75 to 85% of such individuals will develop emphysema, tobacco smoking is still the most important risk factor for COPD even in this group. Targeted screening suggests between 1.0 – 4.5% of patients with COPD have underlying severe a_1 AT deficiency³⁴. The index of suspicion should be high in younger Caucasian patients with predominantly basal disease and a family history. The diagnosis can be made by measuring serum levels of alpha1 antitrypsin and if reduced, genotyping should be performed.

C5.11 Electrocardiography and echocardiography

Electrocardiography is indicated to confirm arrhythmias suspected on clinical grounds. Multifocal atrial tachycardia is a rare arrhythmia (prevalence < 0.32% of hospitalised patients) but over half the cases reported in the literature had underlying COPD.³⁶ Atrial fibrillation commonly develops when pulmonary artery pressure rises, leading to increased right atrial pressure. Echocardiography is useful if cor pulmonale is suspected, when breathlessness is out of proportion to the degree of respiratory impairment or when ischaemic heart disease, pulmonary embolus and left heart failure are suspected. Patients with COPD may have poor quality images on transthoracic examination and transoesophageal echocardiography may be frequently needed.

Patients with COPD are prone to other conditions associated with cigarette smoking, including accelerated cardiovascular, cerebrovascular and peripheral vascular disease, and oropharyngeal, laryngeal and lung carcinoma. Conversely, there is a high prevalence of COPD among patients with ischaemic heart disease, peripheral vascular disease and cerebrovascular disease and smoking-related carcinomas.³⁷ These patients should be screened for symptoms of COPD, and spirometry should be performed.

C5.12 Trials of Therapy

The evidence supporting the utility of specific diagnostic tests in COPD is typically not of the same strength as that for specific therapies reviewed in subsequent sections. The evidence base for tests used in the diagnosis and monitoring of a number of respiratory diseases at one specialist referral clinic was reviewed by Borrill et al.⁴⁰ They were unable to identify any evidence to support the use of peak flow charts to assess treatment with inhaled steroids in patients with pre-diagnosed COPD. Studies were found that did not support the diagnostic use of trials of therapy with inhaled or oral steroids in COPD. There was no evidence to support the diagnostic use of trials of therapy with short or long acting bronchodilators or oral theophyllines in COPD. However, it should be remembered that absence of evidence is not the same as evidence of absence of utility.