Interoperability is the ability of different systems or components to exchange information in a meaningful way. Interoperability enables information generated by one system to be accessed by another system regardless of their technological differences. 
In healthcare, interoperability is the ability of different health information technology systems to communicate, exchange data and use health information in a meaningful way. Although interoperability of computerized health information systems is most often used in local organizations, sharing data is also a major concern at the federal level. These systems are not designed to communicate with other systems outside the local organization. Ideally, interoperability should follow open standards and support information exchange between different healthcare organizations and meeting this challenge is a major concern for health information technology developers and implementers.
Health information interoperability serves many purposes  depending on the person who uses it:
- For patients, interoperability helps improve the quality and safety of care by improving the quality of data flow, data exchange and access to information
- For healthcare professionals, interoperability improves access to health records and information anytime and anywhere
- For health researchers, health information interoperability facilitates access to medical data
- For health managers, interoperability improves efficiency of data collection, economic and statistical analysis
Electronic health records (EHRs) underwent rapid transformation over the past 50 years. The pace of change greatly increased due to the proclamation of the Health Information Technology for Economic and Clinical Health (HITECH) Act in January 2009. 
EHRs made their first appearance in U.S. history in the late 1960s when multiple similar efforts up sprang around the country. The most well-known milestones of EHR development include Lockheed Corporation’s creation of a system featuring computerized physician order entry for El Camino Hospital. Other milestones of EHR development include the deployment of Health Evaluation through Logical Processing system by 3M and the creation of Regenstrief Medical Record System in 1972. 
Dr. Clem McDonald of Regenstrief Institute expected their medical record system to solve three problems in the hospital setting, namely:
- Reduce work of clinical bookkeeping
- Eliminate problems associated with paper records such as unavailable or undecipherable clinical records
- Increase medical record accessibility to clinical and epidemiological outcomes and management research
The greatest challenge to EHR system design surfaced in the 1990s when a growing number of users started adopting EHR in their medical practices. The opening of this fast-growing market tested the limits of commercial vendors. They could not quickly adapt to the new opportunity. They were too accustomed to the unique demands of different inpatient markets such as physician specific workflows, integrated billing, manageable footprint and intra-organizational interoperability. 
While most systems advanced in hardware and software technology, EHR adoption among providers did not catch up as expected with technical advances. Fragmentation of healthcare delivery allowed each hospital and physician to practice medicine the way they wanted to, thereby encouraging EHR system customization according to their needs. EHR systems were not standardized because neither the hospital nor the private practicing physicians were not standardized. System designers tried with little success to force-fit paper oriented workflows into the computer-based system. The lack of common standards prevented sharing of data across care settings. 
With the proclamation of the HITECH Act, two highly disruptive market forces, Medicaid and Medicare, further disturbed the equation. The Centers for Medicare and Medicaid Services (CMS) recognized this cap in EHR capabilities and decided to give incentives to physicians who chose to invest in the systems. Since physicians were not demanding EHR systems on their own, CMS was able to motivate the fragmented customer base to act like a single customer with a coherent demand, thereby promoting standardization in the healthcare industry. Interoperability with other systems and EHR features became the main requirements of EHR meaningful use. 
Health information interoperability has a three-layered structure or component , namely:
Foundational interoperability allows data exchange from one information technology system to be received by another. There is no requirement for the receiving information system to interpret the data. This might involve sending an image, free text, or a pdf document.
Structural interoperability defines the structure or format of the message format standards (syntax). This is used when the data being exchanged is standardized and uniform between the sending and receiving systems and therefore the clinical or operational meaning of the data remains intact. Structural interoperability ensures that data exchanges between systems can be interpreted at the data field level.
Semantic interoperability provides interoperability at the highest level that delivers shared meaning between different systems. This approach leverages the structure and degree of codification of the data, including vocabulary, which allows the receiving system to interpret the incoming data. In most cases, two different EHR systems do not use the same terminology. For example, one system defines a blood test as Fasting Glucose while another system defines the same test Fasting Blood Sugar. Semantic interoperability provides the vocabulary translation between systems making meaningful data exchange possible between disparate EHR systems, business information systems, medical devices, and mobile technologies.
Tools & Techniques
Model-driven health tools
The model-driven health tools are essential for the establishment of a modeling framework and infrastructure. They are needed to develop seamless nationwide health IT standards for model sharing, open communication and standard development within the healthcare sector and health IT community. By using model-driven health tools, health information can have automated validation tools, automated publication of implementation guides and JAVA implementation API for the models. Furthermore, development time and cost will be reduced by providing clear documentation of healthcare initiatives and supporting implementation resources. 
Electronic health records
Electronic health records are the digital version of patients’ charts. EHRs go beyond the use of paper-based patient records by including patients’ medical history, diagnosis and treatment plan, as well as their laboratory results and radiology images. Aside from these, EHRs give healthcare providers access to evidence-based tools that enable them to make better decisions regarding their patients’ healthcare needs. Electronic health records are the focus of health information interoperability experts. Achieving EHR interoperability will facilitate better workflow and efficient data transfer between EHR systems and promote smoother healthcare delivery. 
ICD-10 is the tenth revision of the International Statistical Classification of Diseases and Related Health Problems. It is the new medical classification list released by the World Health Organization (WHO) after ICD-9 became obsolete. As endorsed by AHIMA, ICD-10 is essential to improve the quality of health information needed to meet the demands of a growing global and electronic healthcare environment. Modern electronic health records and interoperable information systems need a modern health classification such as ICD-10 for reporting data and summarizing healthcare information. In fact, ICD-10 is now considered an integral part of EHR systems to achieve information interoperability in all levels of the healthcare sector. 
AHIMA called for the implementation of SNOMED-CT as the new standard clinical terminology to facilitate health information exchange within the national health information network. The new standard will improve interoperable exchange of health information between different systems using standard electronic health records. AHIMA expects that this new standard in clinical terminology will help improve access to legible clinical data that links to medical knowledge to support real-time decision-making of healthcare practitioners. The standard will also expedite care delivery, reduce duplicate testing and prescribing, and identify relevant patient information to facilitate automatic patient reminders and practitioner alerts. This will improve the ability to perform queries to review the quality of care for benchmarking, interpreting effectiveness and measuring quality improvement. 
Best practices and standards for health information interoperability exist to facilitate the communication between health information systems in a uniform manner across systems, organizations, states and national boundaries.  Following the standard practices at the regional and national level boosts the potential power to share health information between healthcare organizations and enables eHealth initiatives.
Interoperability has various levels and each level indicates the complexity of health information exchange. 
Non-electronic information uses minimal technology to share data and most of the health information gathered is recorded on paper. An example of this type of health information exchange is the referral from a primary care unit to a secondary care unit using a paper-based referral letter.
- Machine transportable information – This type of health information exchange transmits non-standardized data using the most basic form of information technology. The most recognized example of this kind of information sharing is paper-based health information through fax or email attachments.
- Machine organizable information – Machine organizable information is the use of structured electronic messages to transmit non-standardized data. An interface is required for this type of information exchange to transfer data across one or more systems.
- Machine interpretable information – Machine interpretable information uses structured messages with coded and standardized data to transmit information across different systems. This type of health information exchange uses a format and a vocabulary that is easily understood by the receiver even without an interface to decode such information.
Health information professionals should first understand the type and level of operability that is needed for proper planning to share health information. This will facilitate the integration of any system and achieve the desired outcomes. Interoperability has six dimensions. These dimensions provide the framework for the types of interoperability needed when developing an integrated healthcare solution. It helps providers select the level and type of interoperability needed to achieve the desired exchange of health information .
- Uniform movement: Healthcare information should be preserved when transmitted between systems.
- Uniform presentation: Different providers using different systems should view healthcare information in the same visual format when needed.
- Uniform visual interface controls: Consistent context and navigational control should be established across various systems.
- Uniform safeguarding of data security and integrity: Information technology professionals should ensure that only authorized users and programmers have access to data in transmission between systems.
- Uniform protection of confidentiality: Confidentiality should always be protected by ensuring strong information governance controls across organizations involved in healthcare information sharing.
- Uniform assurance of a common degree of system service quality: Information technology professionals should always ensure that interoperable systems are reliable. They should make sure that emergency plans are in place in case a breakdown of communication occurs between systems.
Interoperability depends on both syntax and semantics. Health information technology professionals should always ensure that interoperability standards address the requirements of these two types of interoperability. The following are the standard categories applied in healthcare:
- Messaging standards – Messaging standards guide the formulation of structure, content and data requirements needed for electronic message, the unit of information sent from one system to another, by enabling the effective and accurate sharing of healthcare information.
- Terminology standards – These are a set of standards that provide specific codes for terminologies and classifications of clinical concepts such as medications and diseases. Terminology systems assign a unique code to each specific disease or entity and these terminologies, in turn, are used to capture clinical information at the point of care.
- Document standards – Document standards classify the type of information included in a document. In the healthcare sector, this information may be in the form of Subjective, Objective, Assessment, Plan (SOAP) standard, HL7 Clinical Document Architecture used for electronic sharing of documents, HL7 continuity of care document and discharge summary.
- Conceptual Standards – Conceptual standards ensure that neither the meaning nor context of information is lost during its transmission between systems.
- Application standards – These standards ensure the implementation of business rules for software systems when systems interact with each other.
- Architecture standards – These standards define the generic model for health information systems. They guide the planning and designing of new systems by allowing the integration of health information systems.
The application of interoperability in healthcare information across different organizations and levels reaps many benefits  including:
Improvement of risk management
Proper application of interoperability in healthcare information results in reduction of patient risks, improvement in patient safety and better patient management outcomes. With interoperability between systems, the aggregation, analysis and communication of patient information become more efficient. Interoperability enables evidence-based decision-making by healthcare providers while preventing the occurrence of adverse events.
Improvement of patient health outcomes and quality patient care
Healthcare providers who take advantage of the interoperability feature of electronic health information and access the health information of the entire population of patients their organization has can evaluate the needs of their patients more meaningfully, according to the specific health problems they face. Providers can also formulate preventive measures for public health issues. By using standardized EHRs, they can better manage patients and specific risk factors for more desirable patient outcomes.
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- Summary of Joint Position on Adoption of ICD-10. (n.d.). Retrieved September 21, 2015, from https://www.amia.org/
- Implementation of SNOMED-CT Needed to Facilitate Interoperable Exchange of Health Information. (n.d.). Retrieved September 21, 2015, from http://library.ahima.org/xpedio/groups/public/documents/ahima/bok1_028156.hcsp?dDocName=bok1_028156
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