Example of CDA limitations to interoperability: time intervals

The HL7 Clinical Document Architecture (CDA) is an XML-based markup standard intended to specify the encoding, structure and semantics of clinical documents for exchange. CDA is an ANSI-certified standard from Health Level Seven (HL7).  The CDA is highlighted as a flexible framework that can contain any type of clinical content.  Additionally, the details of the encoding of clinical data and associated aspects of that data are intentionally designed to be flexible.

That flexibility provides freedoms in various different systems' ability to export clinical data.  However, that same flexibility is an increasing barrier to the interoperability of data as systems need to import that same data.  My biggest pet peeve with the CDA and this problem is the flexibility that the CDA provides in the encoding of time intervals.

Based on clinical reason, the CDA provides the freedom to encode time intervals in eight (8) (VIII) different representations.

<low>
<width>
<high>
<low> <width>
<low> <high>
<center>
<center> <width>

This amount of flexibility in expressing something as simple as a time interval is an obstacle for any receiving system hoping to import and parse an HL7 CDA-based XML document without knowing the way that the generating system is going to express something as basic as a time interval. This permissive nature of the CDA's artifacts is common beyond this one basic example.

What is needed, and hopefully addressed in the emerging FHIR specification, is a more constrained approach to the foundational aspects of clinical data, such as how to encode time intervals.  To reach a point with more interoperability of healthcare data, analysis is needed of the presence of types of structured clinical data concepts and associated clinical codes used operationally.

I feel that the healthcare standards community ultimately needs to identify a strict and simple constrained set of ways of expressing clinical concepts that healthcare Standards Development Organizations (SDOs) like HL7 should use to constrain existing permissive and complex standards.  This could also be done to guide a stricter and simpler implementation to support interoperability via FHIR.

This could introduce significant and radical improvements in the interoperability of patient data in the US healthcare industry.  This will better enable disparate healthcare software systems to work together without requiring point-to-point coordination.  This could reduce, and eventually eliminate, these problems of point-to-point coordination that result in islands of automation.

This "loose coupler" approach will encourage HL7, or possibly new healthcare SDOs, to embrace a core set of strict and simple required attributes, over the current state of the practice using permissive and complex attributes.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. © Rob McCready, 2014.