COPD has an insidious onset and usually presents in older people. A history of productive cough, wheezing, and shortness of breath, particularly with exercise, is typical. Patients may complain of fatigue as a result of disrupted sleep secondary to constant nocturnal cough and persistent hypoxia and hypercapnia. The patient's smoking history, occupational exposures, and any family history of lung disease should be determined.
Patients with COPD may also present with acute, severe shortness of breath, fever, and chest pain during acute infectious exacerbation.
Examination may show tachypnoea, respiratory distress, use of accessory muscles, and intercostal retraction. Barrel chest is a common observation. There may be hyper-resonance on percussion, and distant breath sounds and poor air movement on auscultation. Wheezing, coarse crackles, clubbing, and cyanosis, as well as signs of right-sided heart failure (distended neck veins, loud P2, hepatomegaly, hepatojugular reflux, and lower-extremity oedema), may be present. Occasionally patients may exhibit asterixis - loss of postural control in the outstretched arms (commonly known as a flap) caused by hypercapnia. This is due to impaired gas exchange in lung parenchyma, worsens with exercise, and is suggestive of respiratory failure.
Spirometry is the first test for diagnosis of COPD and for monitoring disease progress. Patients with COPD have a distinctive pattern seen on spirometry, with a reduced FEV1 and FEV1/FVC ratio. The presence of airflow limitation is defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria as a post-bronchodilator FEV1/FVC <0.70.  In cases where FVC may be hard to measure, forced expiratory volume at 6 seconds (FEV6) can be used.  Chest x-ray (CXR) is rarely diagnostic but can help to exclude other diagnoses. Pulse oximetry screens for hypoxia.
In addition to airflow limitation, the 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. 
The number of previously treated exacerbations (2 or more per year) is the best predictor of having another exacerbation. In addition to previous exacerbations, airflow limitation <50% is predictive of exacerbations.
The GOLD guideline uses a combined COPD assessment approach to group patients according to symptoms and previous history of exacerbations. Symptoms are assessed using the mMRC or CAT scale.
Group A: low risk (0-1 exacerbation per year, not requiring hospitalisation) and fewer symptoms (mMRC 0-1 or CAT <10)
Group B: low risk (0-1 exacerbation per year, not requiring hospitalisation) and more symptoms (mMRC≥ 2 or CAT≥ 10)
Group C: high risk (≥2 exacerbations per year, or one or more requiring hospitalisation) and fewer symptoms (mMRC 0-1 or CAT <10)
Group D: high risk (≥2 exacerbations per year, or one or more requiring hospitalisation) and more symptoms (mMRC≥ 2 or CAT≥ 10).
Patients presenting with acute symptoms should have full blood count, ECG, chest x-ray, and assessment of gas exchange (pulse oximetry and/or arterial blood gas analysis).  Spirometry is not recommended in an acute exacerbation as it may be hard to perform and not very accurate. 
In an acute exacerbation, empirical antibiotics should be given if the patient has three cardinal symptoms: increase in dyspnoea, sputum volume, and sputum purulence; or if the patient has two of the cardinal symptoms, if increased purulence of sputum is one of the two symptoms; or if the patient requires mechanical ventilation. In patients with frequent exacerbations, severe airflow limitation, and/or exacerbations requiring mechanical ventilation, sputum should be sent for culture. 
Detailed pulmonary function tests performed in specialist pulmonary function laboratories can measure diffusing capacity of the lung for carbon monoxide (DLCO), flow volume loops, and inspiratory capacity. They are not used routinely but can be helpful in resolving diagnostic uncertainties and for preoperative assessment. 
In young patients (<45 years) with a family history or with rapidly progressing disease and lower lobe changes on imaging tests, alpha-1 antitrypsin level should be checked. 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.  This may aid in family screening and counselling.
Computed tomography scans show anatomical changes, but their usefulness in diagnosis is confined to patients considered for surgery and for ruling out other pathologies. 
Pulse oximetry should be used to assess all patients with clinical signs of respiratory failure or right heart failure. If peripheral arterial oxygen saturation is less than 92%, then arterial or capillary blood gases should be measured. 
Obstructive sleep apnoea is associated with increased risk of death and hospitalisation in patients with COPD. 
Exercise testing can be useful in patients with a disproportional degree of dyspnoea.  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 also of use in selecting patients for rehabilitation. Respiratory muscle function may also 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. 
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