ICD-9 Codes Do Not Identify All Strokes in Atrial Fibrillation Patients

Jonathan Thigpen, PharmD Assistant Professor Clinical and Administrative Sciences Notre Dame of Maryland University School of PharmacyMedicalResearch.com Interview with:
Jonathan Thigpen, PharmD
Assistant Professor
Clinical and Administrative Sciences
Notre Dame of Maryland University School of Pharmacy

Medical Research: What is the background for this study? What are the main findings?

Dr. Thigpen: This effort assessed the accuracy of International Classification of Disease 9th Edition (ICD-9) stroke codes in identifying valid stroke events in a cohort of atrial fibrillation (AF) patients. The initial electronic search yielded 1,812 events across three stroke centers (Boston Medical Center, Geisinger Health System, and University of Alabama). All ICD-9 identified stroke events were vetted through manual chart review with final adjudication by a stroke neurologist. Atrial fibrillation was verified by evidence via electrocardiogram at stroke admission, 6 months prior to, or 90 days after stroke admission.

In addition to assessing the accuracy of the stroke codes alone, we also assessed the accuracy of stroke and Atrial fibrillation codes combined as well as the accuracy of stroke codes when seeking for stroke associated with Atrial fibrillation. These additional steps give readers insight as to the accuracy and reliability of using ICD-9 codes alone to create a stroke plus AF cohort. We feel that this effort is extremely important given the increasing reliance on ICD-9 codes as a means of identifying stroke events and covariates in research, especially research using administrative data.

The positive predictive value (PPV) of stroke codes alone was 94.2%. PPVs did not differ across clinical site or by type of event (ischemic vs. intracranial hemorrhage). PPV of stroke codes did differ by event coding position (primary vs. other; 97.2% vs. 83.7%) and by ischemic stroke code (433 vs. 434; 85.2% vs. 94.4%). When combined with validation of Atrial fibrillation codes, the PPV of stroke codes decreased to 82.2%. After excluding ischemic stroke due to a different mechanism (eg, vascular procedure, tumor, sepsis) the PPV dropped further to 72.8%. As a separate exercise, manual review confirmed 33 (7.2%) ischemic strokes in 458 events coded as “without infarction”.

Medical Research: What should clinicians and patients take away from your report?

Dr. Thigpen: These results indicate that ICD-9 stroke codes alone have limited use in identifying acute strokes in the setting of active Atrial fibrillation. Manual verification of stroke is needed to confirm stroke events in the setting of AF so as to reduce potential bias.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Thigpen: Future research could build on our study in the following ways.

Firstly, there is limited knowledge concerning the accuracy of ICD-10 stroke codes.
Secondly, our study (and other previous literature) indicates several screening methods that tend to lead to higher coding accuracies (ie, only using stroke codes in the primary position).
Further optimizing ICD-9 screening methods so as to limit the inaccuracies of stroke codes will potentially help better establish ICD stroke codes as a reliable tool for case and covariate ascertainment.


Validity of International Classification of Disease Codes to Identify Ischemic Stroke and Intracranial Hemorrhage Among Individuals With Associated Diagnosis of Atrial Fibrillation

AHA publication:Jonathan L. Thigpen, Chrisly Dillon, Kristen B. Forster, Lori Henault, Emily K. Quinn, Yorghos Tripodis, Peter B. Berger, Elaine M. Hylek, and Nita A. Limdi

Circ Cardiovasc Qual Outcomes. 2015;CIRCOUTCOMES.113.000371published online before print January 13 2015, doi:10.1161/CIRCOUTCOMES.113.000371

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Last Updated on January 17, 2015 by Marie Benz MD FAAD