C5. Further investigations

Further investigations may be necessary to confirm or exclude other conditions and assess COPD severity [evidence level III-2, strong recommendation]

Further investigations are often required to confirm a COPD diagnosis. Some common investigations may be required to identify differential or co-existing causes of airway narrowing or hyper- responsiveness, or both, such as chronic asthma and airway disease, or occupational exposures. In addition to spirometry, general practitioners (GPs) may play a role in initiating, co-ordinating and interpreting some diagnostic tests for respiratory review, referral, and screening. The following diagnostic tests and procedures are often co-ordinated or conducted by GPs in Australia. Detailed interpretation and complex cases may require further specialist consultation.

C5.1 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 accurate for the diagnosis of COPD (den Harder 2017) as hyperinflation is not specific, and will not exclude a small lung nodule (<1cm).

C5.2 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.

C5.3 Electrocardiography

Cardiovascular disease is common in patients with chronic obstructive pulmonary disease but is often under-recognised. Electrocardiography (ECG) may be useful to alert the clinician to its presence. In a retrospective Dutch study of patients entering pulmonary rehabilitation, ischaemic changes were present on ECG in 21% of all patients and in 14% of those without reported cardiovascular co-morbidity (Vanfleteren 2011). Electrocardiography is also 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 (McCord 1998). Atrial fibrillation commonly develops when pulmonary artery pressure rises, leading to increased right atrial pressure.

C5.4 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. Harrison et al 2014 performed a multicentre prospective study of exacerbations of COPD requiring hospital admission in 1343 patients with spirometry confirmed COPD. The authors reported the novel finding of an association between thrombocytosis (>400/mm3 on admission) and mortality. Thrombocytosis (after controlling for confounders) was associated with an increased 1 year all-cause mortality and an increased in hospital mortality (OR 1.53 (95% CI 1.03 to 2.29, p=0.030) and OR 2.37 (95% CI 1.29 to 4.34, p=0.005)) respectively (Harrison 2014) [evidence level III-2].

The Thoracic Society of Australia and New Zealand Alpha1 Antitrypsin Deficiency Position Statement indicates that testing for alpha1 antitrypsin deficiency (AATD) should be considered in all patients with chronic airflow obstruction (Dummer 2020).  The prevalence of severe homozygous AATD has been estimated at approximately 1 in 4,500 in European populations (Blanco 2006). Available data from 15 cohorts in Australia and New Zealand suggest that the prevalence of affected individuals is around 1 in 4,000 (de Serres 2002). Tobacco smoking is still the most important risk factor for COPD even in this group.

C5.5 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.