Which ICD-9 codes were assigned for malignant mesothelioma in the mortality data in the United States before the ICD-10 was introduced?

Background: Malignant mesothelioma (MM) is rare and fatal; survival in most cases is only about one year. Mortality rate is, therefore, a good proxy measure of incidence rate. However, the specific International Classification of Diseases (ICD) code for MM was not available until the Tenth Revision ICD (ICD-10). Little is known on which Ninth Revision ICD (ICD-9) codes were assigned for MM in the ICD-9 era. Methods: We used a 1996 double-coded mortality file compiled by the National Center for Health Statistics to calculate the detection rate (DR) and confirmation rate (CR) of selected ICD-9 codes. Results: Of 2386 decedents whose underlying cause of death was MM (ICD-10 code C45), the DR (deaths) of corresponding ICD-9 code was 57% (1365) for code 199 “malignant neoplasm without specification of site;” 19% (448) for code 162.9 “malignant neoplasm of trachea, bronchus, and lung, unspecified;” 13% (310) for code 163 “malignant neoplasm of pleura;” and 11% (271) for other codes. The CR (deaths) for the aforementioned three ICD-9 codes were 4.0% (1365/33,942), 0.3% (448/150,342), and 70.8% (310/438), respectively. Conclusions: The three ICD-9 codes (199, 162.9, and 163) were the most commonly used codes for MM and composed nine-tenths of all MM deaths in the years before the ICD-10 was introduced. Using only ICD-9 code 163, the code most often used as the surrogate measure of MM in mortality studies in the ICD-9 era, capture may have been only 13% of all MM deaths in the US, and the estimated number of MM deaths missed in 1996 would be 2086.