Magnitude of Impact, Overall and on Subspecialties, of Transitioning in Radiology from ICD-9 to ICD-10 Codes

Purpose: Converting the nation's International Classification of Diseases (ICD) diagnosis coding system, from 14,025 ICD-9 to 69,823 ICD-10 codes, is projected to have enormous financial and operational implications. We aimed to assess the magnitude of impact that this code conversion will have on radiology claims.

Methods: The most frequently billed ICD-9 diagnosis codes for 588,523 radiology claims from five hospitals and affiliated outpatient sites during a 12-month period were mapped to matching ICD-10 codes using a Medicare-endorsed tool. The code-conversion impact factor was calculated for the entire radiology system, and each individual subspecialty division.

Results: Of all ICD-9 codes, only 3,407 (24.3%) were used to report any primary diagnosis. Of all claims, 50% were billed using just 37 (0.3%) primary codes; 75% with 131 (0.5%), and 90% with 348 (2.5%). Those 348 ICD-9 codes mapped onto 2,048 ICD-10 codes (5.9-fold impact), representing just 2.9% of all ICD-10 codes. By subspecialty, the conversion impact factor varied greatly, from 1.1 for breast (11 ICD-9 to 12 ICD-10 codes) to 28.8 for musculoskeletal imaging (146 to 4,199). The community division, reflecting a general practice mix, saw a conversion impact factor of 5.8 (254 to 1,471).

Conclusions: Fewer than 3% of all ICD-9 and ICD-10 codes are used to report an overwhelming majority of all radiology claims. Although the number of commonly used codes will expand 5.9-fold overall, musculoskeletal imaging will experience a projected 28.8-fold explosion. Radiology practices should target their ICD educational and operational conversion efforts in an evidence-based manner.