Administrative data are frequently used to identify venous thromboembolism (VTE) for research and quality reporting. However, the validity of these codes, particularly in outpatients, has not been well-established.
To determine how well International Classification of Diseases, Ninth Revision (ICD-9) codes for VTE predict chart-confirmed acute VTE in inpatient and outpatients.
We selected 4642 adults with an incident ICD-9 diagnosis of VTE between years 2004 and 2010 from the Cardiovascular Research Network Venous Thromboembolism cohort study. Medical charts were reviewed to determine validity of events. Positive predictive values (PPVs) of ICD-9 codes were calculated as the number of chart-validated VTE events divided by the number with specific VTE codes. Analyses were stratified by VTE type [pulmonary embolism (PE), deep venous thrombosis (DVT)], code position (primary, secondary), and setting [hospital/emergency department (ED), outpatient].
The PPV for any diagnosis of VTE was 64.6% for hospital/ED patients and 30.9% for outpatients. Primary diagnosis codes from hospital/ED patients were more likely to represent acute VTE than secondary diagnosis codes (78.9% vs. 44.4%, P<0.001). Primary hospital/ED codes for PE and lower extremity DVT had higher PPV than for upper extremity DVT (89.1%, 74.9%, and 58.1%, respectively). Outpatient codes were poorly predictive of acute VTE: 28.0% for PE and 53.6% for lower extremity DVT.
ICD-9 codes for VTE obtained from outpatient encounters or from secondary diagnosis codes do not reliably reflect acute VTE. More accurate ways of identifying VTE in outpatients are needed before these codes can be adopted for research or policy purposes.
*Division of Hospital Medicine, University of California, San Francisco
†Division of Research, Kaiser Permanente Northern California, Oakland, CA
‡Department of Pharmacotherapy, University of Utah College of Pharmacy, Salt Lake City, UT
§Office for Health Services, Marshfield Clinic Research Foundation, Marshfield, WI
∥Geisinger Health System, Center for Health Research, Danville, PA
¶Scripps Translational Science Institute, La Jolla, CA
#Departments of Epidemiology, Biostatistics and Medicine, University of California, San Francisco
**Department of Health Research and Policy, Stanford University School of Medicine, Palo Alto, CA
Supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health (Grants R01HL103820 and U19HL91179).
M.C.F., S.H.S., and J.R.S.: received grant support from the National Heart, Lung, and Blood Institute of the National Institutes of Health. A.S.G. received grant support from the National Heart, Lung, and Blood Institute of the National Institutes of Health, Astra-Zeneca, Sanofi, and CSL Behring. The remaining authors declare no conflict of interest.
Reprints: Margaret C. Fang, MD, MPH, Division of Hospital Medicine, University of California, 533 Parnassus Avenue, Box 0131, San Francisco, CA 94143. E-mail: firstname.lastname@example.org.