A standards-based clinical information system for HIV/AIDS

To create a clinical data repository to interface the Veteran's Administration (VA) Decentralized Hospital Computer Program (DHCP) and a departmental clinical information system for the management of HIV patients. This system supports record-keeping, decision-making, reporting, and analysis. The database development was designed to overcome two impediments to successful implementations of clinical databases: (i) lack of a standard reference data model, and; (ii) lack of a universal standard for medical concept representation.

Health Level Seven (HL7) is a standard protocol that specifies the implementation of interfaces between two computer applications (sender and receiver) from different vendors or sources of electronic data exchange in the health care environment. This eliminates or substantially reduces the custom interface programming and program maintenance that would otherwise be required. HL7 defines the data to be exchanged, the timing of the interchange, and the communication of errors to the application. The formats are generic in nature and must be configured to meet the needs of the two applications involved. The standard conceptually operates at the seventh level of the ISO model for Open Systems Interconnection (OSI). The OSI simply defines the data elements that are exchanged as abstract messages, and does not prescribe the exact bit stream of the messages that flow over the network. Lower level network software developed according to the OSI model may be used to encode and decode the actual bit stream. The OSI protocols are not universally implemented and, therefore, a set of encoding rules for defining the exact representation of a message must be specified. The VA has created an HL7 module to assist DHCP applications in exchanging health care information with other applications using the HL7 protocol. The DHCP HL7 module consists of a set of utility routines and files that provide a generic interface to the HL7 protocol for all DHCP applications.

The VA's DHCP core modules are in standard use at 169 hospitals, and the role of the VA system in health care delivery has been discussed elsewhere. This development was performed at the Miami VA Medical Center Special Immunology Unit, where a database was created for an HIV patient registry in 1987. Over 2,300 patient have been entered into a database that supports a problem-oriented summary of the patient's clinical record. The interface to the VA DHCP was designed and implemented to capture information from the patient treatment file, pharmacy, laboratory, radiology, and other modules.

We obtained a suite of programs for implementing the HL7 encoding rules from Columbia-Presbyterian Medical Center in New York, written in ANSI C. This toolkit isolates our application programs from the details of the HL7 encoding rules, and allows them to deal with abstract messages and the programming level. While HL7 has become a standard for healthcare message exchange, SQL (Structured Query Language) is the standard for database definition, data manipulation, and query. The target database (Stitt F.W. The Problem-Oriented Medical Synopsis: a patient-centered clinical information system. Proc 17 SCAMC. 1993:88-93) provides clinical workstation functionality. Medical concepts are encoded using a preferred terminology derived from over 15 sources that include the Unified Medical Language System and SNOMed International ( Stitt F.W. The Problem-Oriented Medical Synopsis: coding, indexing, and classification sub-model. Proc 18 SCAMC, 1994: in press). The databases were modeled using the Information Engineering CASE tools, and were written using relational database utilities, including embedded SQL in C (ESQL/C). We linked ESQL/C programs to the HL7 toolkit to allow data to be inserted, deleted, or updated, under transaction control. A graphical format will be used to display the entity-rel