Test establishes FEV1 and FVC. The ratio of these two values indicates whether airflow obstruction is present. COPD severity is classified based on the patient's FEV1 and its percentage of the predicted FEV1. In cases where FVC may be hard to measure, FEV6 (forced expiratory volume at 6 seconds) can be used.
Spirometry should be performed after administering an adequate dose of at least one short-acting inhaled bronchodilator to minimise variability.
Spirometry in practice
Spirometry technique and interpretation
FEV1/FVC ratio <0.70; total absence of reversibility is neither required nor the most typical result
In addition to airflow limitation, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recognise the importance of exacerbations in affecting the natural course of COPD, and place emphasis on assessment of symptoms, risk factors for exacerbations, and comorbidities.
The Modified British Medical Research Council (mMRC) questionnaire or the COPD Assessment Test (CAT) are recommended to assess symptoms. These can be found in the GOLD guidelines. GOLD cautions against the use of the mMRC dyspnoea scale alone for assessing patients, as symptoms of COPD go beyond dyspnoea alone. For this reason, the CAT is preferred. However, GOLD acknowledges that the use of the mMRC scale is widespread, and so a threshold of an mMRC grade ≥2 is still included to define 'more breathless' patients, as opposed to 'less breathless' patients, in its assessment criteria.
mMRC score ranges from 0-4; CAT score ranges from 0-40: mMRC ≥2 or CAT score ≥10 indicates higher symptoms burden
Checked as part of vital signs on acute presentation. A good pulse wave should be picked up by the device. In patients with chronic disease, an oxygen saturation of 88% to 90% may be acceptable.
If <92% arterial or capillary blood gases should be checked.
low oxygen saturation
Checked in patients who are acutely unwell, especially if they have an abnormal pulse oximetry reading. Should also be performed in stable patients with FEV1 <35% predicted or with clinical signs suggestive of respiratory failure, or if peripheral arterial oxygen saturation is <92%.
Hypercapnia, hypoxia, and respiratory acidosis are signs of impending respiratory failure and possible need for intubation.
PaCO₂ >50 mmHg and/or PaO₂ of <60 mmHg suggests respiratory insufficiency
Seldom diagnostic, but useful in ruling out other pathologies.
Increased anteroposterior ratio, flattened diaphragm, increased intercostal spaces, and hyperlucent lungs may be seen.
May also demonstrate complications of COPD, such as pneumonia and pneumothorax.
This test may be considered to assess severity of an exacerbation and may show polycythaemia (haematocrit >55%), anaemia, and leucocytosis. UK guidelines advise FBC in all newly diagnosed patients.
raised haematocrit, anaemia, possible increased WBC count
Risk factors for COPD are similar to those for ischaemic heart disease, so comorbidity is common. Right-sided heart failure may develop in longstanding COPD (cor pulmonale).
signs of right ventricular hypertrophy, arrhythmia, ischaemia
Detailed pulmonary function tests performed in specialist pulmonary function laboratories can measure flow volume loops and inspiratory capacity. They are not used routinely but can be helpful in resolving diagnostic uncertainties and for preoperative assessment.
Diffusing capacity of the lung for carbon monoxide (DLCO) was previously only measured in specialist laboratories; however, portable systems are now available, allowing measurements to be taken in the field. International guidelines from GOLD recommend a DLCO measurement if a patient with COPD has dyspnoea that is disproportionate to their degree of airflow obstruction. A low DLCO value (<60% predicted) in a patient with COPD is associated with decreased exercise capacity, worse health status, and increased risk of death. 
obstructive pattern, decreased DLCO (<60% predicted)
Provides better visualisation of type and distribution of lung tissue damage and bulla formation than CXR.
In contrast to smoking-related COPD, alpha-1 antitrypsin deficiency mainly affects lower fields.
Useful in excluding other underlying pulmonary disease, such as bronchiectasis or lung cancer, and for preoperative assessment. Annual low-dose CT scan (LDCT) is recommended by the US Preventive Services Task Force for lung cancer screening in patients with COPD that is due to smoking.
May be used to exclude asthma if there is diagnostic uncertainty.
<20% diurnal or day-to-day variability
In patients with frequent exacerbations, severe airflow limitation, and/or exacerbations requiring mechanical ventilation, sputum should be sent for culture.
Low level in patients with alpha-1 antitrypsin deficiency. Test is done if there is high suspicion for alpha-1 antitrypsin deficiency, such as a positive family history and atypical COPD cases (young patients and non-smokers). The World Health Organization recommends that all patients with a diagnosis of COPD should be screened once, especially in areas with high prevalence of alpha-1 antitrypsin deficiency.
should be normal in patients with COPD that is related to smoking
Can be of value in patients with a disproportional degree of dyspnoea compared with spirometry. It can be performed on a cycle or treadmill ergometer, or by a simple timed walking test (e.g., 6 minutes, or duration <6 minutes). Exercise testing is of use in selecting patients for rehabilitation.
poor exercise performance or exertional hypoxaemia is suggestive of advanced disease
Obstructive sleep apnoea, a common finding in patients with COPD, is associated with increased risk of death and hospitalisation in patients with COPD.
elevated apnoea-hypopnoea index and/or nocturnal hypoxaemia
Respiratory muscle function may be tested if dyspnoea or hypercapnia are disproportionately increased with respect to FEV1, as well as in patients with poor nutrition and those with corticosteroid myopathy.
reduced maximal inspiratory pressure
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