Investigations
1st investigations to order
oxygen saturation on pulse oximetry
Test
Recommended to be performed for all patients with a possible acute exacerbation of COPD, when available. It should be performed when vital signs are obtained. During an episode, oxygen saturation is frequently depressed below the patient's baseline level, and supplemental oxygen and arterial blood gas testing should be considered if the level is <90%.
Result
depressed below the patient's baseline level
chest x-ray
Test
Rarely diagnostic; principal purpose is to exclude alternate diagnoses. A chest x-ray should be performed in people with moderate to severe disease and where pneumonia or other potential diagnoses (e.g., pneumothorax, congestive heart failure, pleural effusion) are being considered.
Result
hyperinflation, flattened diaphragms, increased retrosternal airspace, bullae, and a small, vertical heart
ECG
Test
Cardiovascular disease is common in people with COPD.[127] Additionally, the possibility of a myocardial infarction, pneumothorax, or pulmonary embolus should be considered if chest tightness or other chest discomfort is present. Patients with COPD are at higher risk to develop cardiac ischemia and/or arrhythmias that can also lead to dyspnea.
How to perform an ECG: animated demonstrationResult
may be right heart enlargement or right ventricular strain, arrhythmia, ischemia
ABG
Test
ABG testing should be performed for people with a moderate to severe acute exacerbation of COPD, to detect chronic hypercarbia and assess for acute respiratory acidosis. Comparison of results to prior baseline ABG is crucial (when available). Acute respiratory acidosis may be a sign of impending respiratory failure. Venous blood gas sampling is not considered a reliable alternative measure.[128]
PaO2 <60 mmHg indicates potential respiratory failure. PaO2 <50 mmHg, PaCO2 ≥45 mmHg, or pH <7.35 indicate a potentially life-threatening illness that requires consideration for intensive care and initiation of assisted ventilation.[129]
Result
respiratory acidosis and compensatory metabolic alkalosis
CBC with platelets
Test
Should be considered for patients with moderate to severe exacerbations to screen for abnormalities that may suggest additional medical disorders such as infection or anemia.
Result
may show elevated hematocrit, elevated WBC count or anemia
electrolytes, BUN, + creatinine
Test
Should be considered for 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. Patients with renal insufficiency may have metabolic acidosis that can increase ventilatory demand.
Result
usually normal
Investigations to consider
sputum culture + Gram stain
Test
In severe disease, and if the patient's sputum is purulent and hospitalization is being considered, a sputum Gram stain and culture should be obtained to assess for potential bacterial pathogens that may have triggered the episode.
Result
may suggest bacterial infection
respiratory virus diagnostics
Test
In severe disease and, if hospitalization is being considered, testing for respiratory virus pathogens (where feasible) should be considered both to identify any treatable agent (e.g., influenza), and to identify the need for use of expanded infection control precautions.
Result
may confirm viral infection
cardiac troponin
Test
Elevations in cardiac troponin can occur due to unrecognized myocardial injury resulting from COPD exacerbation. Elevations in troponin may be associated with increased mortality.[130]
Result
normal if no myocardial injury
CT scan of chest
Test
May be useful to exclude alternate diagnoses, including tracheobronchomalacia and especially pulmonary embolus, if the diagnosis and basis of respiratory decompensation remains uncertain after routine chest x-ray.
Result
normal if no pneumonia, pleural effusion, malignancy, pulmonary embolus, or tracheobronchomalacia present
Emerging tests
procalcitonin
Test
Emerging as a promising biomarker for the diagnosis of bacterial infections as it tends to be higher in severe bacterial infections and low in viral infections. The Food and Drug Administration has approved procalcitonin as a test for guiding antibiotic therapy in patients with acute respiratory tract infections. 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 lead to lower antibiotic consumption, and lower risk for antibiotic-related side effects in all patients including those with acute exacerbation of COPD.[115] Further research is required to establish its use in clinical practice. It should not be used to guide antibiotic use in patients with severe COPD exacerbations requiring intensive care.[116]
Result
may be elevated in severe bacterial infections and low in viral infections
C-reactive protein
Test
C-reactive protein (CRP) is also being investigated as a potential biomarker to guide the use of antibiotics during exacerbations of COPD. A decision to withhold antibiotics, based on low CRP levels at the point of care, has been associated with reduced antibiotic prescriptions without worse clinical outcomes.[117][118][119]
Result
may be elevated in bacterial infections
eosinophil count
Test
The eosinophil count may become a useful indicator of likelihood of benefit from systemic corticosteroids.[1]
Evidence indicates that systemic corticosteroids (generally a 5-day course of oral prednisone) can shorten recovery time from a COPD exacerbation. Recent studies suggest that systemic corticosteroids may be less effective in treating exacerbations in patients with lower levels of blood eosinophils.[120][121][122][123] After stabilization of the acute episode, the blood eosinophil level can also help to guide the decision on whether the patient will benefit from inhaled corticosteroids to reduce the risk of further exacerbations.
Result
corticosteroids may be less effective in treating exacerbations in patients with lower levels of blood eosinophils
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