The Maryland Health Services Cost Review Commission (HSCRC) provides ambulatory surgery (AS) and emergency department (ED) records to HCUP in two separate files. One file contains information from ambulatory surgery centers that are associated with acute care hospitals. Data from freestanding ambulatory surgery centers are not included. The second file contains ambulatory care data from emergency departments, clinics, and labor/delivery centers within acute care, general hospitals in Maryland.

Because the Maryland AS file does not include ICD-9-CM procedure codes, only CPT-4 procedure codes are considered in assigning records to the 2003 SASD. For the 2003 SEDD, the presence of a revenue code indicating ED services (range 450-459) is the reason for inclusion. The Maryland outpatient source records are separated as follows:

• 21% of source records are assigned to the SASD
• 63% of source records are included in the SEDD
• 16% of source records are excluded.

The excluded records include labor/delivery and clinic services such as aftercare, non-traumatic joint disorders and HIV infection. As noted previously, the Maryland source file includes these other types of outpatient services.

Charge File for the Maryland SEDD. Maryland provided summarized charge detail in which charge information is summed within the revenue center. This type of Charges file includes one record per discharge abstract. Each record contains three corresponding arrays with the following information: revenue center (REVCDn), total charge for the revenue center (CHGn), and total units of service for the revenue center (UNITn). For example, if a patient had 5 laboratory tests, REVCD1 would include the revenue code for laboratory, CHG1 would include the total charge for the 5 tests, and UNIT1 would be 5.

2001 SASD. The data supplied to HCUP came in two files, each with a different format. Data for January to June were in one format, and data for July to December were in an expanded format. The July to December file contained data elements that were not provided for the first half of the year.

Identifying Freestanding Facilities. Starting in 1998, the data element FREESTANDING identifies hospital-based and freestanding ambulatory surgery facilities. Prior to 1998, there are two identifiers on the SASD that allow a researcher to identify hospital-based and freestanding ambulatory surgery centers.

• DSHOSPID is the facility identifier provided by the data source.
• AHAID is the facility identifier used by the American Hospital Association.

1997 Maryland SASD. There are 52 unique DSHOSPID values in the 1997 MD SASD. All should be considered hospital-based facilities.