The creation of a nationwide electronic records system in the United States would require a way to identify individual patients out of about 300 million people and then link the patient to the record.

Each record could contain hundreds or even thousands of pages of clinical notes and digital images such as X-rays.

Technology is not the only challenge, because such a system also raises privacy concerns. But potential models might be found in Canada and New Zealand.

The easiest way to address concerns would be to issue every U.S. resident a unique identifier or use Social Security numbers tied to a central database of medical records. But the idea of a national identity system has always met with stiff resistance in the United States, so either approach won't garner much support, said Dr. Carol Diamond, managing director of the Markle Foundation's health care program.

Dr. David Brailer, national coordinator for health
information technology at the Department of Health and Human Services, said the department is still working out the policies, standards and architecture for a National Health Information Network, but it has already decided not to base the network on a unique patient identifier.

Brailer said development of patient indexes - possibly linked to records stored in multiple places - was an alternative to the use of national identifiers.

Kelly Cronin, senior adviser to Dr. Mark McClellan, administrator of the Centers for Medicare and Medicaid Services, said she agreed that developing master, cross-referenced patient indexes linked to one another and to clinical records could help resolve the technology and privacy challenges associated with a national electronic health record (EHR) system. But she added that "no one has yet identified the solution for a client registry."

Diamond said the Markle Foundation and its Connecting for Health project support the use of an index approach, along with probabilistic matching, which would ensure that the index links to the correct set of records for each patient.

This technology is similar to what Internet search engines use and would eliminate the need for a national identifier and ensure the accurate linkage of data, Diamond said. He added that HHS leaders don't have to look far to find out how such an approach would work.

Last year, the Canadian province of Newfoundland and Labrador completed development of a Unique Person Identifier/Client Registry based on probabilistic matching of patient records with an indexed client registry.

Autry Dawe, technical lead for the registry at Newfoundland and Labrador's Centre for Health Information, said the province's system will serve as the model for developing a pan-Canadian client registry.

When other provinces set up their registry systems, clinicians in one province will be able to link to records in another province, enabling practitioners to easily tap into the home records of a traveling patient. Dawe included an index-based system to make it easier to add patients from other countries to the registry - a more difficult task with a system based on a national identifier.

The Newfoundland and Labrador registry was developed with funding from Canada Health Infoway, the federally funded, nonprofit corporation spearheading health care IT in Canada. The registry uses sophisticated algorithms to match patient records in hospitals and doctors' offices with the index. The algorithm looks for common data points, such as birth dates and addresses, to ensure that the correct records match each patient.

When the algorithm cannot resolve a match - for example, records for two John Smiths in the same town - then a team at the center examines the records to ensure the correct match is made. If necessary, this team calls clinicians and patients for verification.

Mark Battaglia, senior vice president for development and international operations at Initiate Systems, which provided Newfoundland and Labrador with its enterprise master person index for the registry, said the company also provides software to help with manual audits.

The index approach helps resolve privacy concerns, Battaglia added, because it isolates the identifier from the clinical record and supports the use of decentralized databases. Battaglia would not say that Initiate has a 100 percent success rate - "my lawyers won't let me" - but he said the company's health care clients, which include large companies that manage patients' pharmacy benefits, have reported few errors.

New Zealand took the index approach to linking patients and records 20 years ago, said Debbie Chin, deputy director-general of corporate and information at the New Zealand Ministry of Health. She said the New Zealand National Health Index (NHI) has been around so long "it's like water. We take it for granted."

Like Newfoundland and Labrador's registry, NHI uses computers to match patients and records, and human intervention to weed through possible duplicates.

NHI also separates identity information from clinical information and is linked to a separate medical warning system that sends electronic alerts to clinicians about possible dangers in a treatment regimen, such as potentially adverse drug interactions.

Whether the United States eventually adopts the index model is still an open question, but New Zealand and Newfoundland and Labrador have already proved that such a system can serve as the engine for a broad-based EHR without the need for a national identifier.