Will ICD-10 Change How We Define Comorbidities, Complications?

On October 1, 2015, the U.S. healthcare system transitioned from an ICD-9 based coding system to the much more detailed ICD-10 coding system. As often happens when a new system of procedure classification is introduced, unintended consequences emerged.

A new paper from a Duke University Medical Center team in Durham, North Carolina, found that the transition from the International Classification of Diseases, Ninth Revision (ICD-9) to ICD-10 changed in important ways how healthcare systems defined comorbidities and postop complications among patients who underwent primary total hip or knee arthroplasty (THA or TKA).

Their work, “Trends in Comorbidities and Complications Using ICD-9 and ICD-10 in Total Hip and Knee Arthroplasties,” appears in the April 21, 2021 edition of The Journal of Bone and Joint Surgery.

Tetsu Ohnuma, M.D., M.P.H., Ph.D., an anesthesiologist and co-author, told OTW, “Administrative claims data sets are used to report observational trends, cost, and surgical outcomes, and studies using those data rely on the use of ICD codes to define comorbidities, complications, and procedures. However, the transition from ICD-9 codes to ICD-10 codes on October 1, 2015 created challenges due to the greater specificity of ICD-10 codes. Therefore, we looked at a potential impact on comorbidities and medical complications before and after the transition.”

The researchers gathered information on comorbidities and medical complications from the Premier Healthcare database from fiscal year (FY)2011 to FY2018.

“We identified approximately two million patients who underwent primary total hip and knee arthroplasties from 2011 to 2018,” explained Dr. Ohnuma to OTW. “The discontinuity before and after the ICD transition in most comorbidities and the comorbidity score was not clinically meaningful. Moreover, generally postoperative medical complications had a decreased trend over time as evidenced by non-significant changes in slope.”

“…Of the comorbidities studied,” wrote the authors, “congestive heart failure, hypertension, and obesity had a statistically significant but clinically small discontinuity after the transition from ICD-9 to ICD-10 coding. Of the complications, pneumonia, acute respiratory failure, sepsis, and urinary tract infection demonstrated statistically significant discontinuity. Alcohol abuse and paralysis had an increasing prevalence before the ICD transition, followed by a decreasing prevalence after the transition. In contrast, metastatic cancer, weight loss, and acquired immunodeficiency syndrome (AIDS) showed a decreasing prevalence before the ICD transition followed by an increasing prevalence after the transition…”

Dr. Ohnuma concluded,“Our findings will support the use of caution when conducting joint replacement studies that rely on ICD coding and include the ICD coding transition period.”