If you spend enough time interacting with clinical applications and terminologies you will hear terminologies described as pre-coordinated or post-coordinated. What I would like to do in this post is provide my explanation of what these terms mean, the impact they have on knowledge representation and analytics and why it matters going forward.
Let's start with the word coordinated. Remember, we are talking about a term, which for our purposes is a stable identifier associated with one or many words meant to express a concept or idea. (term= code + description).
When you create a term, you are coordinating a set of words together into a concept to represent some piece of relevant information. You do this all the time. You did it the last time you ordered an “extra dry grande soy latte with two packets of Splenda” at Starbucks. So, the act of assembling words to express an idea is the act of coordination.
So what about the “Pre-” and “Post-”?
The "pre” and “post” prefixes have to do with when the coordination was performed relative to when a code was assigned (or at least that is how I think about it).
A “Pre-coordinated term” is a term that was coordinated and assigned a code before you needed it.
A “Post-coordinated term” is a term that you assembled from other terms at the point when you needed it. (So the coordination of the notion happened “post” stable code assignment to the TERMs used to represent it.)
A simple, non-healthcare, example is a value-meal at a fast food restaurant. The value-meal is a Pre-coordinated meal. When you walk in and order the value-meal the cashier presses a single button that represents your meal and it is ordered. If, however, you don't want the value-meal and you order items a la cart, the cashier presses however many buttons they need so that they can accurately convey the details of you order. They are “post-coordinating” items together at time of consumption (and thinking you are high maintenance).
When you consider this and think about healthcare terminologies, you quickly come to the realization that we live in a world that is predominantly pre-coordinated. Here is a partial list of terminologies we use in Healthcare that are pre-coordinated:
- FDA NDC
- SNOMED-CT (parts of it)
- HDD (parts of it)
- Most commercial terminologies
- Most local terminologies
Here are some established terminologies that are designed for Post-coordination:
- SNOMED-CT (parts of it)
- HDD (parts of it)
Notice a difference?
Why so many pre-coordinated terminologies in Healthcare?
To answer the question “why?”, lets consider the pros and cons of each coordination approach.
- It is easier to manage a “flat” Pre-coordinated terminology with legacy content management methodologies.
- The fact that they are created ahead of time means that they should always represent a valid concept in the domain.
- It is easy to store in a database. Since it has a single code pointer to a concept it fits into the way we have always thought about terms.
- The entity maintaining the terminology has to Pre-coordinate an idea for it to be represented in the terminology. (You have to order off of the value menu - no substitutions).
- To understand the parts of a term you need to create explicit relationships to other term. In other words the work you did to Pre-coordinate the term is not represented in a structured way.
- In order to represent every possible combination terminologies can become very large.
- Adding a new axis of information can create significant ripples across a terminology and require a large amount of maintenance to instantiate.
- Since clinical decision support is often triggered on primitive concepts, complex Pre-coordinated terminologies must be pessimistically linked in order to work. For example, in the CMS quality measures there is a measure that excludes patients if they have had an X-ray procedure. In order to drive this rule that notion “x-ray procedure” is linked to hundreds of Pre-coordinated LOINC and CPT terms that have in them the notion of “X-ray procedure”. In a well defined post coordinated terminology this would be a single link to the modality “x-ray”. This issue can be solved ontologically but requires a fair amount of work behind the scenes.
- Smaller, primitive terminologies designed to be assembled into complex post-coordinated terms.
- Consumer can “build their own” notion based on the primitives.
- Decision support rules can be driven by post coordinated partial assemblies and use optimistic linking.
- Without some rational grammar a consumer could post-coordinate an invalid notion from the available parts. This means that a well designed Post-Coordinated terminology would have a grammar where necessary to prevent this from happening.
- We would need to consider how we store and represent post-coordination in our applications.
- Post coordinated terminologies are ontological in nature. This means maintaining them is not a simple as a flat list of terms.
When you examine the pros and cons (which are almost reciprocals of one another) you can see that Pre-coordinated terms are the easy path for those of us that build software and content (at least initially) and Post-coordinated terms are better for the consumer trying to leverage the software in their care process.
Where does one approach make sense versus another?
Pre-coordination is a reasonable approach when you are dealing with a domain that has finite boundaries. Medications are a good example of this. There are a finite number of combinations of ingredients, dose forms and strengths. This gives the person coordinating those notions a solid basis to say “these are the valid terms in this domain”.
The inverse of this is a domain where there are an infinite number of potential combinations, like Problems. In a Pre-coordinated terminology if you want to represent fractures you need to associate the notion “fracture” with any bone that can be fractured. If you want to further denote the type of fracture you take those notions and associate them with each fracture type. If you want to say the patient has a “history of” fracture, you do it again. Anyone that has taken a close look at ICD10-CM knows what happens form there. On top of all this, it doesn’t take much for you to realize that the concept you want to express has not been Pre-coordinated... So you pick the closest thing you can...and information is lost. '
A terminology in a domain that has an infinite or even a very large combination of notions should ultimately be represented by a post-coordinated terminology.
If post-coordination is better in some circumstances, what is stopping us from adopting it in healthcare?
Anything that represents a fundamental change is hard. It is even harder if the change is something that is not felt directly by the consumer or when it is designed to improve something later. As long as we chase short term, buzzword oriented, goals and ignore the strategic evolutionary adaptation required for a well positioned clinical architecture, we will continue to fall short of becoming the awesome sidekick we can become.
There is movement in this direction. SNOMED-CT has been heralded as a terminology that supports post coordination. It needs some work, but it is a good starting point. I have also been told that ICD11 is based on post coordination...
RadLex is based on post-coordination but has struggled to gain adoption. I think the existing post-coordinated terminologies have struggled because:
- Post-coordinated terminologies are deceptively complex to manage, especially using legacy oriented tools.
- They try to straddle the worlds of Pre/Post-coordination.
- They try to leverage overly generalized, academically oriented structures.
- We, as an industry, have not been ready for them.
At ClinicalArchitecture we are building technologies that will help our partners evolve the way they use terminology, regardless of how it is coordinated. The truth is, if you are building an EHR system you just want the terminology to work and do so in a way that allows you to delight your customers. This is one of the reasons we started the company back in 2007. This fundamental shift is not going to be easy and as long as the entire industry is running, heads down, it will not happen.
Someone needs to be focused on solving this problem of plumbing...Someone is.
Come by and see us at HIMSS - we will show you what the future looks like (and give you some cool stuff).
If any of my learned collegues in the industry would liek to add their thoughts please feel free to add your comments.