Study investigates ambiguities in ICD coding for respiratory infections

Background and goal: The International Classification of Diseases (ICD) system standardizes diagnostic codes globally, enabling accurate comparisons of health data. This study investigated regional differences in respiratory infection diagnoses in Poland to identify potential ambiguities in ICD coding and their implications for data comparability.

Study approach: Researchers analyzed over 292 million primary care visits for acute respiratory infections in Poland between 2010 and 2019, using ICD-10 codes (J00–J22). Diagnosis data were grouped by age (children, working-age adults, elders) and analyzed at the county level. Statistical methods and visualizations were used to uncover regional differences in how ICD codes were applied. These inconsistencies were further analyzed to determine whether they reflected genuine differences in diagnoses or systemic issues with code usage.

Main results:

• The most problematic code appeared to be "acute upper respiratory infections of multiple and unspecified sites" (J06), which was frequently used interchangeably with other codes, especially "common cold" (J00) and "bronchitis" (J20)

• Significant differences were observed in how respiratory conditions were coded across counties, with no consistent regional patterns to explain these variations. Larger counties showed less variability, likely due to random factors canceling out.

Why it matters: Variation in physician coding practices requires particular attention during analyses to avoid conclusions about differences that may simply be coding variation.