A 45-year-old patient tells an advanced practice registered nurse (APRN) about a productive cough that is worse in the morning. The sputum is clear or white. Shortness of breath occurs with exertion, especially after exercise. The patient reports smoking a half a pack of cigarettes each day for the past 15 years. Vital signs are within normal limits with the exception of a respiratory rate of 26 breaths per minute. Assessment reveals rhonchi and wheezing bilaterally. The APRN suspects that chronic obstructive pulmonary disease (COPD) is present and performs a diagnostic test to confirm the suspicion. Which diagnostic test result supports the APRN's diagnosis?

While a low hematocrit can suggest chronic hypoxia, it is not a definitive indicator of COPD. Hematocrit levels can be influenced by various factors, including hydration status and other underlying conditions. Thus, while it may provide some context about the patient's overall health, it does not directly confirm the presence of COPD.

A forced expiratory volume in one second (FEV1) of 80% suggests that the patient has a normal or mildly reduced lung function. In COPD, FEV1 is typically less than 70% of the expected value, indicating significant airflow obstruction. Therefore, an FEV1 of 80% does not align with the expected pulmonary function test results for a COPD diagnosis.

Peak flow measurements can help assess the severity of asthma or other obstructive conditions but are less definitive for diagnosing COPD. A peak flow rate of 75% indicates reduced airflow but does not provide the specific information needed to confirm COPD. COPD diagnosis is better established through spirometry and imaging, making this choice less relevant.