OBJECTIVES:  Generally, coding specificity increased with International Classification of Diseases, 10^thEdition (ICD-10). However, for chronic obstructive pulmonary disease (COPD), the opposite is true. COPD is no longer easily differentiated from chronic obstructive asthma (COA), which is now included within the COPD ICD-10 code range (J41-J44). This analysis examined the impact of this coding difference on COPD-related healthcare utilization (HCU) and costs measurement, and determined appropriate ICD-9 codes to ensure consistency in COPD studies spanning the ICD-9/10 transition. METHODS:  The sample included COPD patients aged ≥40 years from a large US claims database who initiated long-acting bronchodilator monotherapy between 1/1/2008 and 1/31/2015. Patients had ≥1 year of continuous enrollment pre- and post-treatment initiation. Monthly COPD-related HCU and costs (2015 consumer price index-adjusted) were ascertained while patients remained on long-acting bronchodilator monotherapy. Claims were considered COPD-related if there was a COPD diagnosis in any position according to two different coding definitions: 1) COPD (ICD-9 [491.xx, 492.x, or 496] or ICD-10 [J410, J411, J418, J42, J430, J431, J432, J438, J439, J440, J441, J449]); and 2) COPD+COA (ICD-9 493.2x). RESULTS:  Analysis included 27,394 patients; mean±SD age 68±10 years; 50% female; and 60% on Medicare. During a mean±SD post-index period of 192.7±308.0 days, 69.0%, 9.3%, and 12.0% of patients had ≥1 COPD-related ambulatory visit, emergency department visit, or inpatient admission, respectively, according to definition 1; and 69.6%, 9.5%, and 12.2% per definition 2. Mean±SD monthly COPD-related costs were $1,205.5±$4,063.1 and $1,222.0±$4,093.0, according to definitions 1 and 2, respectively. CONCLUSIONS:  Among COPD patients initiating long-acting bronchodilator monotherapy, the impact of including ICD-9 codes for COA when ascertaining COPD-related HCU and costs was minimal. Therefore, inclusion of ICD-9 codes for COA is unnecessary to maintain coding consistency in studies spanning the ICD-9/10 transition. This analysis should be replicated in other COPD populations to confirm these findings.