Chronic Obstructive Pulmonary Disease Diagnostics

Laboratory Tests and Ancillaries

Spirometry

Spirometry is the recommended measurement of airflow limitation that confirms the diagnosis of COPD. It is a useful tool in the assessment of the severity of the pathological changes in COPD. Spirometry is used in the follow-up assessment of patients with documented COPD to help make therapeutic decisions and to identify rapid decline. It is also recommended for patients at risk of COPD, especially smokers >40 years old with cough, sputum, or dyspnea. 

Its use must be restricted to patients needing essential or urgent tests to diagnose COPD or to assess lung function status in patients for surgery or interventional procedures during increased COVID-19 (coronavirus disease 2019) prevalence in the community.

It measures forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV₁). A decreased FEV₁/FVC ratio is typically seen in patients with COPD. A post-bronchodilator FEV₁/FVC <0.7 confirms the presence of non-fully reversible airflow obstruction and is mandatory to establish COPD diagnosis.

According to the 2025 Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) report, a pre-bronchodilator spirometry can be used as an initial test to determine if airflow obstruction is present in a symptomatic patient; if obstruction is not present (FEV₁/FVC ratio of ≥0.7), a post-bronchodilator spirometry is not recommended unless there is very high clinical suspicion of COPD. Patients with a pre-bronchodilator FEV₁/FVC ratio <0.7 that increases ≥0.7 post-bronchodilator have increased risk of developing COPD and should be monitored regularly. 

Spirometry should be performed following quality control services. Lung volumes are affected by the process of aging and FEV₁/FVC ratio depends on age, height, sex, and race.

If without access to spirometry, the diagnosis of COPD may be suspected based on history, symptoms, and physical signs. Peak flow measurements may be used to rule out asthma, but not to diagnose COPD, and it has a good sensitivity rate but weak specificity.

The Modified British Medical Research Council (mMRC) Dyspnea Scale is useful for classification, which can be used to assist in the evaluation of disease severity and functional disability.

*Reference: Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: 2025 report.

COPD Assessment Test (CAT) is a short questionnaire used in routine clinical practice to gauge the health status of patients with COPD. CAT measures the patients’ disease severity using 8 symptoms, with scores ranging from 0-40:

• Frequency of cough
• Chest tightness
• Limitations with home activities
• Presence of sleep disturbance
• Degree of the presence of phlegm
• Breathlessness when climbing stairs or walking uphill
• Confidence with outdoor activities even if with COPD
• Level of energy

Other Laboratory Tests

Bronchodilator Reversibility Testing

The bronchodilator reversibility testing is usually performed only once at the time of diagnosis. It may help rule out asthma, establish the best attainable lung function, evaluate prognosis, and guide treatment decisions. However, it may not reliably predict response to long-term bronchodilator therapy.

Pulse Oximetry and Arterial Blood Gas (ABG) Measurement

Pulse oximetry should be performed in stable patients, especially those with FEV₁ of <35% predicted or with signs of respiratory failure or right heart failure. ABG should be assessed when the peripheral saturation is <92%.

Alpha-1 Antitrypsin Deficiency (AATD) Screening

AATD screening is a recommended procedure by the World Health Organization (WHO) and the European Respiratory Society (ERS) for all patients diagnosed with COPD, especially in alpha-1 antitrypsin deficiency-prevalent areas. It may be useful in young patients (<45 years) who develop COPD. Positive results may lead to family screening and counseling. An alpha-1 antitrypsin serum concentration of <15-20% of the normal value is highly suggestive of homozygous alpha-1 antitrypsin deficiency.

Diffusing Capacity of the Lungs for Carbon Monoxide (DL_CO)

DL_CO is used to evaluate the gas transfer properties of the respiratory system. A low DL_CO (<60% predicted) is associated with decreased exercise capacity, increased symptoms, worse health status, and increased risk of death.

In smokers without airflow limitation, values <80% predicted signal an increased risk for developing COPD over time.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Polymerase Chain Reaction Assay

SARS-COV-2 PCR assay is recommended for COPD patients with new or worsening respiratory symptoms, fever, and other symptoms which could be COVID-19 related. Reverse transcriptase-polymerase chain reaction (RT-PCR) for SARS-CoV-2 is also recommended prior to performing spirometry or bronchoscopy. 

Blood Eosinophil Count  

Blood eosinophil count is recommended by GOLD to guide clinicians in using inhaled corticosteroids as part of the pharmacological management of COPD. There is evidence that blood eosinophil counts are higher in COPD on average, although marked overlap with controls was noted. Higher blood eosinophil count in COPD patients is associated with increased lung eosinophil numbers and markers of type-2 inflammation.

Imaging

Chest X-ray

A chest X-ray is useful mainly in ruling out alternative diagnoses. It may show signs of lung hyperinflation (eg flattened diaphragm), lung hyperlucency, and rapid tapering of the vascular markings. It may be considered in COPD patients with moderate to severe symptoms of COVID-19 or worsening respiratory status.

Computed Tomography (CT) Scan

CT scan is not routinely used but may help in excluding other possible diagnoses. It is recommended if surgical management is being contemplated. It may also be considered in patients with persistent exacerbations, symptoms out of proportion to disease severity based on lung function testing, FEV1 of <45% predicted with significant hyperinflation, or patients meeting the criteria for lung cancer screening. It is also suggested for lung cancer screening in COPD patients due to smoking.