BASE MA Encounter Files

Medicare Advantage Organizations (MAOs) submit encounter data to document diagnoses among their enrolled Medicare Advantage (MA) beneficiaries; the diagnosis information is used by Medicare to determine the MAO’s capitated reimbursement. Although there have been concerns that the encounter data may not accurately capture diagnoses and procedures, preliminary analyses of the SEER-Medicare encounter data indicate that the encounter data capture this information on a similar level to the fee-for-service (FFS) claims data.

Brief summaries are provided below for each Medicare BASE (i.e., files obtained directly from CMS) MA encounter data file included in SEER-Medicare. Additional links with more details are provided below to CMS’s Research Data Assistance Center (ResDAC) and Chronic Conditions Warehouse (CCW) websites. Investigators should note that given SEER-Medicare privacy policies, some variables, namely identifiers of persons and providers and geographical locations such as zip codes, have been encrypted.

Additional Resources

For Medicare beneficiaries with MA coverage, encounter data are available for two cohorts: persons with and without cancer (see Summary Table of Available Data for more specifics). Beginning October 1, 2015, the coding system for diagnosis codes and procedure codes was switched from ICD-9 to ICD-10.

Inpatient

The inpatient file contains Part A encounters by calendar year for institutional inpatient services. There is overlap of information included in this inpatient encounter file and the MedPAR file. While the MedPAR file does contain complete inpatient information for fee-for-service (FFS) enrollees, it’s not a complete source of inpatient care among Medicare Advantage (MA) enrollees. This is because hospitals are not billing CMS directly for MA patients, the MA records included in the MedPAR are “information only” bills or “shadow bills.” Hospitals send these records to CMS to maintain an accurate count of the services they provide to Medicare beneficiaries, because some payments to hospitals are adjusted based on the number of Medicare patients seen (for example, payments to disproportionate share hospitals, or payments for graduate medical education.) Because not all hospitals participate in these programs, the MedPAR file does not reliably capture all inpatient stays for MA enrollees.

There are multiple parts to this file: base file, revenue center file, condition code file, occurrence code file, span code file, and value code file.

View ResDAC’s Carrier (Encounter) File OverviewExternal Web Site Policy
View CCW’s Medicare Encounter Record Layout and Codebook (PDF)External Web Site Policy

Skilled Nursing Facility

The skilled nursing facility (SNF) file contains encounters by calendar year. There is overlap of information included in this SNF encounter file and the MedPAR file. While the MedPAR file does contain complete SNF information for fee-for-service (FFS) enrollees, it’s not a complete source of SNF stays for Medicare Advantage (MA) enrollees. This is because SNFs are not billing CMS directly for MA patients, the MA records are included in the MedPAR as “information only” bills or “shadow bills.” SNFs send these records to CMS to maintain an accurate count of the services they provide to Medicare beneficiaries, because some payments to SNFs are adjusted based on the number of Medicare patients seen (for example, payments to disproportionate share hospitals, or payments for graduate medical education.) Because not all SNFs participate in these programs, the MedPAR file does not reliably capture all SNF encounters for MA enrollees.

There are multiple parts to this file: base file, revenue center file, condition code file, occurrence code file, span code file, and value code file.

Carrier

The carrier file includes encounter records largely from physicians although the file also includes encounters from other non-institutional providers such as physician assistants, clinical social workers, nurse practitioners, independent clinical laboratories, ambulance providers, and stand-alone ambulatory surgical centers. In addition to including diagnosis codes, the carrier encounter records include dates of service, encrypted provider numbers (e.g., NPI) and Health Care Procedure Classification Code (HCPCS) to describe the nature of the encounter. The HCPCS is composed primarily of CPT-4 codes developed by the American Medical Association, with additional codes specific to CMS.

Carrier Encounter Details:

  • Carrier records are non-institutional encounters; however, this does not mean that they are outpatient encounters. Providers, such as physicians, provide services in the office, hospital, or other settings. To identify where the service is provided, one needs to assess the variable "line place of service", which specifies the place of service.
  • There are two subfiles – base file and line file. The base file contains the overall encounter level information. The line file contains the individual service level information from the encounter (e.g., the procedure codes with the diagnosis associated with the procedure, performing provider identifier).
  • There are two pairs of date fields. The fields "claim from" and "claim through" dates cover a period of service (usually but not always a single date of service), while the "line first expense date" and "line last expense date" reflect the specific day of service.

View ResDAC’s Carrier (Encounter) File OverviewExternal Web Site Policy
View CCW’s Medicare Encounter Record Layout and Codebook (PDF)External Web Site Policy

Outpatient

The outpatient file contains Part B encounters by calendar year from institutional outpatient providers. Examples of institutional outpatient providers include hospital outpatient departments, rural health clinics, renal dialysis facilities, outpatient rehabilitation facilities, comprehensive outpatient rehabilitation facilities, community mental health centers. In and out surgeries performed in a hospital will be in the hospital outpatient file. Encounters for surgeries performed in freestanding surgical centers appear in the carrier file, not in the outpatient file.

There are multiple parts to this file: base file, revenue center file, condition code file, occurrence code file, span code file, and value code file.

Some of the information contained in this outpatient file includes diagnosis and procedure codes, dates of service, facility provider number, and beneficiary demographic information. Although the outpatient file contains data fields for ICD-9 or ICD-10 procedure codes, the CPT/HCPCS fields are the main source of information on procedures provided. As with the carrier data, there may be multiple records for the same date of service.

View ResDAC’s Outpatient File OverviewExternal Web Site Policy
View CCW’s Medicare Encounter Record Layout and Codebook (PDF)External Web Site Policy

Home Health Agency (HHA)

The Home Health Agency file contains encounters for home health services. Some of the information contained in this file includes the number of visits, type of visit (skilled-nursing care, home health aides, physical therapy, speech therapy, occupational therapy, and medical social services), diagnosis (ICD-9 or ICD10 diagnosis), the dates of visits, HHA provider number, and beneficiary demographic information. An HHA record may cover services provided over a period of time, not a single day.

There are multiple parts to this file: base file, revenue center file, condition code file, occurrence code file, span code file, and value code file.

View ResDAC’s HHA File OverviewExternal Web Site Policy
View CCW’s Medicare Encounter Record Layout and Codebook (PDF)External Web Site Policy

Durable Medical Equipment (DME)

The Durable Medical Equipment (DME) file contains services provided by Durable Medical Equipment Regional Carriers (DMERCs). Some of the information contained in this file includes diagnosis, (ICD-9 or ICD-10 diagnosis), services provided (HCFA Common Procedure Coding System (HCPCS) codes), dates of service, DME provider number, and beneficiary demographic information. Records for DME services that are processed by a carrier will be found in the Carrier file. Claims for DME services that are processed by DMERCs will be found in the DME file. For example, claims for oral equivalents of IV chemotherapies will be found in the DME file.

There are two parts to this file: base file and line file.

View ResDAC's DME File overviewExternal Web Site Policy
View CCW’s Medicare Encounter Record Layout and Codebook (PDF)External Web Site Policy

Last Updated: 29 Jan, 2024