The impact of changing ICD code on hypertension-related mortality in the southeastern United States from 1994-2005.

Confusion surrounding cardiovascular disease trends arises when measurement and reporting of classification systems such as the International Classification of Diseases (ICD) code are revised. The current study examined the impact of ICD code revision on mortality trends for heart disease, cerebrovascular disease, and diabetes in 16 Southeast states using data published in the 1994-2005 Centers for Disease Control National Vital Statistics Reports. Data were averaged by year and analyzed separately before (1994-1998) and after (1999-2005) the ICD code change, pooled across codes using comparability ratios (1994-2005), and further compared at the year of ICD code change using standard error of 1998 data to determine whether corresponding 1999 rates fell within 95% confidence intervals. The change in classification did not alter Southeast US trends regarding a decrease in heart disease and cerebrovascular disease rates and an increase in diabetes mortality in years 1994-2005. On the other hand, the change in ICD code classification systems did impact mortality rates for heart disease, cerebrovascular disease, and diabetes, suggesting that change in code to ICD-10 in 1999 underestimates heart disease and cerebrovascular disease and overestimates diabetes mortality rates in the Southeast United States. Health and disease burden profiles, which use mortality data to measure health status, need to carefully evaluate and report the influence of ICD code revisions as they draw conclusions. Primary care health providers should question the impact and comparability of ICD revision before accepting mortality trend conclusions.