Chronic obstructive pulmonary disease (COPD): coding considerations

Hospital discharge data

Unless otherwise specified, references in the data to 'COPD' refer to patients with COPD as classified by ICD10 codes J40 - J44 (including all their subsidiary codes) and, in some older data, ICD9 codes 490 - 492 and 496. It should be noted that the coding in the Scottish Morbidity Record (SMR01) changed from ICD9 to ICD10 between March and April 1996.

Mortality data

Mortality data are published by the National Records of Scotland (formerly the General Register Office for Scotland) and the ICD codes used for the analysis of hospital discharge data have also been used for mortality data. The coding scheme changed from ICD9 to ICD10 between December 1999 and January 2000. During this transition, a bridge coding exercise was carried out to code a sample of deaths using both ICD9 and ICD10 systems. This allowed an assessment of the extent of change due specifically to the change in coding systems. The bridge coding exercise recorded 3,018 and 3,144 deaths from COPD (as defined above) respectively. This produced an ICD10/ICD9 comparability ratio of 1.04 suggesting a reasonable degree of comparability between these two coding systems for mortality data.

Primary care data

Clinical coding in primary care in Scotland is currently in transition from the Read coding system to SNOMED CT as part of the implementation of the Digital Health and Care Strategy 2021 and the Health and Social Care: Data Strategy. Primary care statistics presented in this section are based on Public Health Scotland’s Read Code Grouping ‘Bronchitis, emphysema & other chronic obstructive pulmonary disease’ and are detailed below. More information on Read codes can be found on the PHS website.