Assessment of Year-to-Year Patient-Specific Comorbid Conditions Reported in the Medicare Chronic Conditions Data Warehouse.

The Centers for Medicare & Medicaid Services created the Chronic Conditions Data Warehouse (CCDW) for researchers and health policy analysts seeking to improve health care quality and reduce health care costs and use.1 Refreshed annually, the CCDW uses International Classification of Diseases (ICD) codes to identify people enrolled in fee-for-service Medicare who have specific chronic conditions, adding flags to denote these individuals.

We sought to determine whether CCDW condition flags identified using codes from the International Classification of Diseases, Ninth Revision (ICD-9) and International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) persist in a given patient across time. The CCDW algorithms use different numbers of sequential years, or lookback periods, to flag different conditions. We hypothesized that flags based on longer lookback periods (eg, 3 years for Alzheimer disease) and used for conditions unlikely to be cured (eg, schizophrenia) would be more likely to persist in the same patient than flags based on shorter lookback periods (eg, 1 year for anemia) and conditions with high cure rates (eg, hip and pelvic fracture).