Systematic Undercoding of Diagnostic Procedures in National Inpatient Sample (NIS): A Threat to Validity Due to Surveillance Bias.

BACKGROUND AND OBJECTIVES

Health services research often relies on readily available data, originally collected for administrative purposes and used for public reporting and pay-for-performance initiatives. We examined the prevalence of underreporting of diagnostic procedures for acute myocardial infarction (AMI), deep venous thrombosis (DVT), and pulmonary embolism (PE), used for public reporting and pay-for-performance initiatives.

METHOD

We retrospectively identified procedures for AMI, DVT, and PE in the National Inpatient Sample (NIS) database between 2012 and 2016. From January 1, 2012, through September 30, 2015, the NIS used the International Classification of Diseases, Ninth Revision (ICD-9) coding scheme. From October 1, 2015, through December 31, 2016, the NIS used the International Classification of Diseases, Tenth Revision (ICD-10) coding scheme. We grouped the data by ICD code definitions (ICD-9 or ICD-10) to reflect these code changes and to prevent any confounding or misclassification. In addition, we used survey weighting to examine the utilization of venous duplex ultrasound scan for DVT, electrocardiogram (ECG) for AMI, and chest computed tomography (CT) scan, pulmonary angiography, echocardiography, and nuclear medicine ventilation/perfusion () scan for PE.

RESULTS

In the ICD-9 period, by primary diagnosis, only 0.26% (n = 5930) of patients with reported AMI had an ECG. Just 2.13% (n = 7455) of patients with reported DVT had a peripheral vascular ultrasound scan. For patients with PE diagnosis, 1.92% (n = 12 885) had pulmonary angiography, 3.92% (n = 26 325) had CT scan, 5.31% (n = 35 645) had cardiac ultrasound scan, and 0.45% (n = 3025) had scan. In the ICD-10 period, by primary diagnosis, 0.04% (n = 345) of reported AMI events had an ECG and 0.91% (n = 920) of DVT events had a peripheral vascular ultrasound scan. For patients with PE diagnosis, 2.08% (n = 4805) had pulmonary angiography, 0.63% (n = 1460) had CT scan, 1.68% (n = 3890) had cardiac ultrasound scan, and 0.06% (n = 140) had scan. Small proportions of diagnostic procedures were observed for any diagnoses of AMI, DVT, or PE.

CONCLUSIONS

Our findings question the validity of using NIS and other administrative databases for health services and outcomes research that rely on certain diagnostic procedures. Unfortunately, the NIS does not provide granular data that can control for differences in diagnostic procedure use, which can lead to surveillance bias. Researchers and policy makers must understand and acknowledge the limitations inherent in these databases, when used for pay-for-performance initiatives and hospital benchmarking.