A client has been admitted with chronic obstructive pulmonary disease (COPD). Diagnostic tests have been ordered. Which of the tests will provide the most accurate indicator of the client's acid-base balance?

Rationale: A. Bronchoscopy allows for direct visualization of the airways and may be used for sampling or clearing secretions but does not assess acid-base balance. B. Pulmonary function tests evaluate lung volume and airflow but are not specific to acid-base status. C. Pulse oximetry measures oxygen saturation, which reflects oxygenation but not CO₂ levels or pH status. D. Arterial blood gases (ABGs) are the most accurate test for evaluating acid-base balance, as they provide values for pH, PaCO₂, HCO₃⁻, and PaO₂ — essential indicators in COPD management.