Inaccuracy of ICD-9 Codes for Chronic Kidney Disease: A Study from Two Practice-based Research Networks (PBRNs)

Area of Science:

• Medical Informatics
• Nephrology
• Health Services Research

Background:

• Inaccurate International Classification of Diseases, Ninth Revision (ICD-9) coding leads to unreliable research data and potential patient mismanagement.
• Misuse of ICD-9 codes, particularly for chronic kidney disease (CKD), was investigated due to patient reports contradicting their medical records.

Purpose of the Study:

• To determine the prevalence of International Classification of Diseases, Ninth Revision (ICD-9) code misuse for chronic kidney disease (CKD) stage 3.
• To assess the accuracy of ICD-9 code 585.x in reflecting actual CKD diagnoses in electronic medical records (EMRs).

Main Methods:

• A retrospective chart review was conducted on 325 patients with the ICD-9 code for CKD stage 3 (585.3).
• Data were extracted from electronic medical records across three primary care practices in Buffalo, New York, and Kansas City, Kansas.

Main Results:

• Nearly half (47%) of patients with the CKD ICD-9 code lacked clinical indicators of the disease, according to Kidney Disease Outcomes Quality Initiative guidelines.
• The prevalence of accurate CKD diagnosis among patients with the ICD-9 code 585.3 was significantly lower than indicated by the code itself.

Conclusions:

• The ICD-9 code for CKD stage 3 (585.3) does not accurately represent disease prevalence in the studied population.
• Inaccurate coding has clinical implications, potentially leading to unnecessary treatments and tests for patients.
• This coding inaccuracy poses a significant challenge for research relying on EMR data for patient identification and recruitment.