Investigations

1st investigations to order

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Perform in patients with a moderate to severe acute exacerbation of COPD, when there is any evidence of hypercapnia, in all hypoxic patients, in all patients requiring oxygen, and in all patients who seem unwell.

  • Use to detect chronic hypercapnia and assess for acute respiratory acidosis.

  • Ensure you compare results with prior baseline ABG (when available).

  • Document the fraction of inspired oxygen (FiO2) or O2 flow rate of any supplemental oxygen given (controlled oxygen given via a Venturi mask).

    • Performing the ABG while the patient is on controlled oxygen allows the A-a gradient to be established.

  • PaO2 <8.0 kPa (approximately 60 mmHg) indicates respiratory failure.

  • pH <7.35 and PaCO2 >6.5 kPa define acute respiratory acidosis.[93] 

    • Acidaemia implies a severe exacerbation and predicts in-hospital and 30-day mortality.[94] 

  • Repeat the ABG after 30 to 60 minutes of treatment with controlled oxygen and bronchodilators to check for a rise in PaCO2 or a fall in pH.[90] 

  • If possible, perform a blood gas analysis within 30-60 minutes of starting acute NIV. 

    • Although the British Thoracic Society (BTS) recommends performing a blood gas analysis within 2 hours of starting acute NIV,[95]in practice, specialists recommend ideally waiting only 30-60 minutes to check for changes in PaCO2 and pH.

    • Arrange review by a specialist healthcare professional with expertise in managing patients on NIV within 30 minutes if blood gas measurements fail to improve.[95]

  • Venous blood gas sampling is not considered a reliable alternative measure.[96]

Practical tip

Some patients with known hypoxaemia (e.g., those on long-term oxygen therapy) may have low oxygen saturations usually. However, deteriorating oxygen saturation is concerning and should warrant an urgent assessment.


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Result

  • PaO2 <8.0 kPa (approximately 60 mmHg) indicates respiratory failure

  • pH <7.35 and PaCO2 >6.5 kPa define acute respiratory acidosis[93]

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In hospital, use pulse oximetry at presentation to measure oxygen saturations as part of vital signs.[1][90] In the community, use pulse oximetry if there are clinical features of a severe exacerbation.[83]

  • Ensure a good pulse wave is picked up by the device.

  • During an exacerbation, oxygen saturation is frequently depressed below the patient's baseline level.

  • Document the fraction of inspired oxygen (FiO₂) or O₂ flow rate if supplemental oxygen is given.

Result

  • low oxygen saturation, depressed below the patient’s baseline level

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Perform an ECG as cardiovascular disease is common in people with COPD.[97] 

  • Consider a myocardial infarction or pneumothorax if chest tightness or other chest discomfort is present. However, note that chest tightness is also a symptom of COPD due to airflow limitation and chest hyperinflation.

  • Patients with COPD are at higher risk of developing cardiac ischaemia and/or arrhythmias, such as new-onset atrial fibrillation, that can also lead to dyspnoea.


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Result

  • may be right heart enlargement, arrhythmia, ischaemia 

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Perform in patients with moderate to severe exacerbations.

  • Screens for abnormalities that may suggest additional medical disorders, such as infection or anaemia.

Result

  • may show elevated haematocrit, elevated WBC count, or anaemia

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Perform in patients with moderate to severe exacerbations.

  • An abnormal result may suggest additional medical disorders.

  • Patients with COPD exacerbations may have decreased oral intake and may become volume depleted.

Result

  • usually normal

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Perform in patients with moderate to severe exacerbations.

  • An abnormal result may suggest presence of infection.

Result

  • elevated CRP suggests presence of infection

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Request for patients with moderate to severe disease and/or suspected pneumonia.

Can be used to exclude differential or comorbid diagnoses, including pneumothorax, congestive heart failure, and pleural effusion.

Radiological changes seen in COPD include (but be aware these are not diagnostic of an exacerbation):

  • Flattened diaphragm and increased retrosternal air space volume, indicating lung hyperinflation

  • Hyperlucency of the lungs

  • Rapid tapering of vascular markings.[1] 

Result

  • hyperinflation, flattened diaphragm, increased retrosternal air space (seen on lateral x-ray, if performed), bullae, and a small vertical heart suggest COPD, but are not diagnostic for an exacerbation

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Obtain for potential bacterial pathogens that may have triggered the episode. Use in severe disease and if hospitalisation is being considered.

  • Not a routine investigation in primary care.

  • The most frequently identified bacterial pathogens include Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis.[31][51] 

Result

  • may suggest bacterial infection

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Once they are stable, investigate all patients who have required hospitalisation for an exacerbation of COPD for vitamin D deficiency. Vitamin D levels are lower in patients with COPD. Supplementation of patients with severe deficiency results in a reduction in exacerbations and hospitalisation. Assess for severe vitamin D deficiency (<10 ng/mL or <25 nM) and supplement if required.[1]

Result

  • <10 ng/mL or <25 nM indicates severe deficiency

Investigations to consider

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Request if the patient has pyrexia.

Result

  • may indicate sepsis

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Consider in severe disease.

  • Use to identify any treatable agent.

  • Use to identify the need for expanded infection control precautions in hospital.

Result

  • may confirm viral infection

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Assess for an elevation, which would indicate myocardial injury.

  • COPD exacerbations can lead to myocardial injury.

  • Elevations in troponin may be associated with increased mortality.[98] 

Result

  • normal if no myocardial injury

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Measure on admission for patients who are taking theophylline (or aminophylline).[83]

Result

  • therapeutic range: 10-20 mg/L (55–110 micromols/litre) 

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Use to exclude heart failure, a possible differential of COPD exacerbation.

Result

  • normal BNP <100 picograms/mL but some variability according to gender and age

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Use to exclude alternative diagnoses if the diagnosis and basis of respiratory decompensation remains uncertain after routine CXR.

  • May identify a pulmonary embolus, pneumonia, pleural effusion, or a malignancy.

Practical tip

Do not routinely order a chest CT. Only request a chest CT if you suspect malignancy, a pulmonary embolus, or bronchiectasis, or when considering surgery.[1][83] 

Result

  • may still show presence of emphysema, even if no pneumonia, pleural effusion, malignancy, or pulmonary embolus present

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Arrange for all patients admitted to hospital with an acute exacerbation if previous spirometry results are not available to confirm the diagnosis of COPD.[85]

Practical tip

Do not assess the patient using peak flow as an acute investigation. This is not recommended for assessment of an exacerbation due to the results being of lower quality[99] or unreliable. In practice, patients are often unable to perform a good-quality forced expiratory manoeuvre during an acute exacerbation.

Result

  • confirms diagnosis of COPD

Emerging tests

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Procalcitonin is being investigated as a biomarker for the diagnosis of bacterial infections.[100] [101]

  • Higher levels of procalcitonin have been detected in severe bacterial infections.[100] 

  • It may have a function in guiding when to use antibiotics for the treatment of lower respiratory tract infection; however, this is unclear. 

  • A Cochrane review of the use of procalcitonin to guide initiation and duration of antibiotic treatment in people with acute respiratory tract infections found it lowered the risk of mortality, and led to lower antibiotic consumption and lower risk for antibiotic-related side effects in all patients, including those with acute exacerbation of COPD.[100] Further research is required to establish its use in clinical practice. In a separate analysis of 1656 patients, 826 were randomly assigned to a group where the decision on whether to provide antibiotics was based on the results of a procalcitonin assay (830 patients were given usual care).[101] 

  • The assay results did not result in less use of antibiotics.

    • There was no significant difference between the procalcitonin group and the usual-care group in antibiotic-days (mean 4.2 and 4.3 days, respectively; difference −0.05 day; 95% CI −0.6 to +0.5; P = 0.87) or the proportion of patients with adverse outcomes (11.7% [96 patients] and 13.1% [109 patients]; difference −1.5 percentage points; 95% CI, −4.6 to +1.7; P <0.001 for non-inferiority) within 30 days.[101]

Result

  • higher levels of procalcitonin have been detected in severe bacterial infections[100]

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