Accuracy of ICD-9-CM coding of cervical spine fractures: implications for research using administrative databases

ICD-9-CM codes are often used for trauma research due to their ready availability in administrative databases. They are also used to classify injury severity in trauma patients. However, errors in coding may limit the use of these codes. Prior studies have found coding accuracy ranging from 20 to 100%, casting doubt on the reliability of studies utilizing these codes. The goal of this study was to determine the accuracy of ICD-9-CM coding for cervical spine fractures.

We used ICD-9-CM codes to identify trauma admissions and cervical spine fractures at a Level I trauma center in 2006. Cervical spine CT or CTA reports were reviewed by two independent observers. Data were compared to ICD-9-CM codes to determine accuracy.

Of 1620 trauma admissions, 174 (11%) included a cervical spine fracture defined by ICD-9-CM codes. A cervical spine fracture was the primary diagnosis in 79 admissions and a secondary diagnosis in 63 admissions. Of the 142 cervical spine fractures defined by ICD-9-CM code, there were 133 (94%) cervical fractures by radiology report. Accuracy varied by primary diagnosis (97%) versus secondary diagnosis (89%). By cervical level, there were 230 fractures by CT report. Of these, 7% of ICD-9-CM codes documented a fractured level not noted in the CT report. Conversely, 14% of fractured levels noted by CT report did not have a corresponding ICD-9-CM code.

We found an overall 94% accuracy of ICD-9-CM coding compared to radiology reports. Inaccuracy of coding fracture level ranged from 7 to 14%. Researchers using these codes should refer back to the medical record or perform a sensitivity analysis to improve reliability.