1. Clinical Assessment Instruments and the LOINC/SNOMED CT Relationship
Jay Lyle, PhD, eHealth Education USA & JP Systems
Susan A. Matney, PhD, RNC-OB, FAAN, Intermountain Heath Care
SNOMED CT Expo, October 2016

2. LOINC & SNOMED similarities & differences
SNOMED CT
LOINC
Type
Ontology
Nomenclature
Origin
Pathology
Lab observations
Scope
19 conceptual axes, including observables & findings
Lab and Clinical Observations, Radiology, Document Names
Concept Relationships
Yes, explicit
Some (in Class axis)
Synonyms
Yes, including language support
Description Logic support
Yes No
International
Most of you are familiar with these, so we won’t linger. The key difference is in the concept relationships.

3. Using LOINC and SNOMED CT together
Common “best practice”: Use LOINC for questions and SNOMED CT for answers
U.S. ONC Recommendation
Stated in IHTSDO and Regenstrief agreement: “LOINC provides codes that represent the names of information items (e.g. questions) and SNOMED CT provides codes that may represent nominal and ordinal values (e.g. answers) for these named information items. ” (8.3)
LOINC
: Moisture of Skin
Example of the standard pattern. US, Agreement. Not required.
SNOMED CT
: moist skin (finding)

4. 364532007 | Moistness of skin (observable entity) |
Complication 1
SNOMED CT has an “Observable Entity” domain that is semantically the same as LOINC.
Some SNOMED CT concepts are synonymous with LOINC codes.
Some (Lab) LOINC concepts can be expressed as SNOMED CT expressions.
LOINC term/SNOMED CT reference set contains SCT post-coordinated expressions for 9730 Active LOINC terms
How would you choose whether to encode SBP as
8480-6: Systolic blood pressure, or
| Systolic arterial pressure (observable entity) |
This is true for the lab domain. Clinical LOINC domains may also be modeled in SNOMED CT but not under any existing agreement, and results may vary.
EG Vitals work, where we wish to associate qualifiers with Vitals. They seem to be “preconditions” per the observable model, but while some (e.g. body position) are findings, and fit the range of “precondition,” many (exertion phase, sleep status) are qualifiers.
SNOMED CT
| Moistness of skin (observable entity) |
SNOMED CE
: moist skin (finding)

5. Complication 2
LOINC codes may not be added to SNOMED CT, though they may be represented as expressions.
For instance, the options for bilirubin include
| Bilirubin:MCnc:Pt:BldA:Qn, or
 |Observable entity| : 
Towards = | Bilirubin (substance)
 |Property type| =  | Mass concentration (property) (qualifier value) ,
 |Inheres in| =  | Plasma (substance) , 
 |Direct site| =  | Acellular blood (serum or plasma) specimen (specimen), 
 |Scale| =  | Quantitative (qualifier value) ,  
 |Time aspect| =   |Single point in time|
Could you request addition of such a concept without reference to LOINC?
| Towards replaced by  |Component ?

6. These issues don’t impede the pattern
LOINC question, SNOMED CT answer
Unless LOINC question does not exist
Possible to add
Possible to use SNOMED CT Observable
There are consistency, migration questions
Translate LOINC into an expression when needed to support logical operations
For domains supported by agreement

7. Complication 3: Assessment Instruments
Instrument: set of questions with answer values. Not just text; as an instrument, published, vetted, peer-reviewed. Comes with a detailed clinical protocol for evaluation.

8. Questions, defined answers
Questions, defined answers. Numbers are not measures and do not imply proportional relationships: 4 is not twice as good as 2.
One relation does obtain: you add them to obtain a total score, which is a pretty good measure of risk.
So: if you use the LOINC question for skin moisture, can you encode “very moist” in SNOMED?

9. Assessment Instrument Issue 1
The context and complexity of the protocol for assessing these questions is unlikely to be accurately represented in a clinical ontology.
Efforts to do so are likely to render the ontology unfit for representing other complex and specific protocols.
Example of protocol to answer one question
LOINC has code and name, not specification of protocol: that’s the Instrument.
Such descriptions raise the question, how would one model concepts like “linen must be changed at least once a shift”?
The meaning of “2” or of “very moist” is determined by the instrument in which they are found.

10. This is an illustration of difficulty, not a recommendation
Finding: Skin Very Moist ≡
Moist skin (finding)
Interprets
Moistness of skin (observable entity)
Associated with
Changing bed linen (procedure)
Should be groups
Frequency
Every shift (qualifier)
Associated with
Moist skin (finding)
Frequency
Almost every touch (qualifier)

11. Assessment Instrument Issue 2
So you can’t specify the semantics in SNOMED; we do so in the normative answer list.
And we guard against using anything else by making it normative
And we try to emphasize that guardianship with copyright.
The copyright isn’t just a barrier to use; it’s a guide for correct use.

12. Assessment Instrument Issue 3
LOINC answers are strings, not concepts
Although the instrument defines the concept precisely, the LOINC schema treats all answers as reusable strings, with semantics defined by context.
Without definitions or relationships, the semantics are in the instrument Context.
Since they live there, LOINC does not adopt a concept orientation to answer strings.

13. Example of string answer complication
I was looking for an example of a copyright issue and found the LOINC representation of the Broselow Luten tape, which has an even better illustration of the string-vs-concept issue.
“White” was evidently used in a race question earlier, and someone attempted to assert concept permanence by giving it a description. Even so, we see that as a member of a Normative list, White is an authorized answer for this question.

14. Conclusion
Though it’s possible to diverge from the pattern, the LOINC Question/SNOMED CT answer pattern seems to work.
Instruments are different.
Caution: LOINC answers are only meaningful in context of their questions.

15. References
IHTSDO-Regenstrief agreement:
Guidance en-US_INT_ pdf
Doesn’t cover clinical LOINC
Braden Scale
Broselow weight system
CIMI Skin Risk proof-of-concept project

16. Contacts Jay Lyle Susan Matney jay@lyle.net; jay.lyle@jpsys.com