Validation of ICD-9 Codes for Identification of Chronic Overlapping Pain Conditions

J Pain Palliat Care Pharmacother. 2022 Sep;36(3):166-177. doi: 10.1080/15360288.2022.2089437. Epub 2022 Jul 28.


Chronic overlapping pain conditions (COPCs) are a collection of chronic pain syndromes that often co-occur and are thought to share underlying nociplastic pathophysiology. Since they can manifest as seemingly unrelated syndromes they have historically been studied in isolation. Use of International Classification of Diseases (ICD) codes in medical records has been proposed as a means to identify and study trends in COPCs at the population level, however validated code sets are needed. Recently, a code set comprising ICD-10 codes as proxies for 11 COPCs was validated. The goal of this project was to validate a code set composed of ICD-9 codes for the identification of COPCs in administrative datasets. Data was extracted using the Electronic Medical Record Search Engine at the University of Michigan Health System from January 1st, 2011 to January 1st, 2015. The source population were patients with one of the candidate ICD-9 codes corresponding to various COPCs. Natural language searches were used as a reference standard. If code sets met a pre-specified threshold of agreement between ICD-9 codes and natural language searches (≥ 70%), they were retained and diagnostic accuracy statistics were calculated for each code set. Validated ICD-9 code sets were generated for 10 of the 11 COPCs evaluated. The majority had high levels of diagnostic accuracy, with all but one code set achieving ≥ 80% specificity, sensitivity, and predictive values. This code set may be used by pain researchers to identify COPCs using ICD-9 codes in administrative datasets.

Keywords: Chronic overlapping pain conditions; ICD9; administrative data; health services research.

Plain language summary

COPCs share underlying nociplastic etiology; it is important to distinguish these from other pain etiologies to better understand their prevalence, identify comorbid conditions, and understand trends in their pharmacologic management.COPCs have historically been under-recognized and -studied due to challenges with identifying them in administrative datasets.A validated code set for identifying COPCs in administrative datasets using ICD-10 codes exists, however this limits any longitudinal studies as ICD-10 coding was not fully implemented until 2015.This study used natural language searches to validate a set of ICD-9 codes for identifying COPCs.Code sets were able to be validated for 10 of 11 COPCs with high specificity, sensitivity, and predictive values.

MeSH terms

  • Chronic Pain* / diagnosis
  • Databases, Factual
  • Electronic Health Records
  • Humans
  • International Classification of Diseases*
  • Syndrome