Methods and Limitations
We used data from the Agency for Healthcare Research and Quality’s Nationwide Inpatient Sample (NIS) to estimate hospital discharges involving diabetes related Nontraumatic lower extremity amputation (LEA) by levels of amputation. The Nationwide Inpatient Sample contains information on hospital inpatient stays from states participating in the Healthcare Cost and Utilization Project. The NIS provides annual information on approximately 5 million to 8 million inpatient stays from about 1,000 hospitals. The sampling frame for the 2009 NIS is a sample of hospitals that comprises approximately 955 of all hospital discharges in the United States. A more detailed description of the NIS is available.1
Hospital discharges for which diabetes (ICD-9 code 250) was any listed diagnosis were used to examine discharges involving LEA. Cases were defined as discharges having diabetes as a listed diagnosis and an LEA procedure (ICD-9 procedure code of 84.1). Discharges with a traumatic amputation diagnosis code (ICD-9 diagnoses codes 895-897) were excluded. Discharges were categorized according to level of amputation using ICD-9 procedure codes — toe (ICD-9 code of 84.11), foot (ICD-9 codes 84.12-84.13), below knee (ICD-9 codes 84.14-84.16), and above knee (ICD-9 codes 84.17-84.19). LEA hospital discharge rates by amputation level were calculated using estimates of the population with diabetes based on 3-year moving averages from CDC’s National Health Interview Survey. Estimates were age-adjusted on the basis of the 2000 U.S. standard population.
Because NIS data represent hospital discharges and not individual persons, patients with multiple LEA hospitalizations could be counted multiple times. The NIS underestimates the total number of LEA discharges because it does not include LEAs occurring in federal hospitals and outpatient settings. Race-specific rates were not estimated because race was missing for a number of states.2
- Overview of Nationwide Inpatient Sample. Agency for Healthcare Research and Quality, Rockville, MD. (Available at http://www.hcup-us.ahrq.gov/nisoverview.jsp).
- NIS Database Documentation. June 2011. Agency for Healthcare Research and Quality and Centers for Disease Control and Prevention. (Available at http://www.hcup-us.ahrq.gov/db/nation/nis/nisdbdocumentation.jsp).