SNOMED CT Editorial Guide

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Many disorders can occur in combination within the same patient.  Guidance on the modeling and terming of FSNs for disorder combinations aims to achieve consistency.  Clinically significant disorder combinations are represented in SNOMED CT by a single concept so that users can document temporal (timing) and causal (cause/effect) relationships between the conditions. 

Expressing Associations

To express an association between conditions, one of the following associations is used:

  • Simple co-occurrence:  two or more conditions have no direct causal or temporal relationship but are found together more often than by random chance

  • Causation 1:  the cause is another finding or disorder, an event, or procedure

  • Causation 2:  the cause is a physical force, physical object, organism, or substance

  • Temporal association:  the timing of the two conditions occur before, during, or after each other

When considering disorder combinations two questions can be asked:

  1. Is there a causal relationship?
  2. What is the temporal relationship?

The following table provides the possible combinations of answers.  It allows authors to assign combination disorders to a corresponding category below, to which the appropriate modeling and FSN construction is applied. 

 

Is there a stated causal relationship?

Yes, the cause is another finding or disorder, an event, or procedure.

This is causation 1.

Yes, the cause is a physical object or force, organism, or substance.

This is causation 2.

No

What is the temporal relationship?









Not stated

X due to Y

X caused by Y

X and Y should be documented separately

X follows Y

X due to and following Y

N/A

X after Y

X precedes Y

X before Y

N/A

X before Y

X occurs during Y

X due to and during Y

N/A

X during Y

X occurs before, during, and/or after Y

X due to and temporally related to Y

N/A

X temporally related to Y*

*Note:  Temporally related to (attribute) and its subtypes Before and During are only approved to model perioperative complications and a limited number of other clinical findings.



Simple Co-occurrence

Modeling pattern

Naming pattern

Assign each condition as a supertype (or ensure that each participating disorder is present in the ancestor tree following classification)

Use simple co-occurrence for two or more conditions that are strongly associated by means other than causality or a temporal relationship (e.g. a common predisposition) where representing such conditions as separate statements would result in a loss of the associated between the conditions

For example,

Do not use simple co-occurrence for those disorders with more than one anatomical site or more than one associated morphology. Those disorders should rather be represented as individual concepts in a medical record.

FSN: X with Y

Correct examples:

    • Sinusitis with nasal polyps (disorder)
    • Acute bronchitis with bronchiectasis (disorder)

Incorrect examples not to be repeated:

    • Psoriasis-eczema overlap condition (disorder)
    • Hay fever with asthma (disorder)

Be aware of conditions which likely exist prior to a disorder or procedure.

For example, legacy term  609454008 | Induced termination of pregnancy complicated by acute necrosis of liver (disorder)|

Be aware of conditions which likely exist prior to a disorder or procedure.

For example, legacy term  609454008 | Induced termination of pregnancy complicated by acute necrosis of liver (disorder)|




Causation 1

Cause is another finding, disorder, event, or procedure

Modeling pattern

Naming pattern

For a condition caused by a clinical finding/disorder

  • Assign the causal disorder as the target of a Due to relationship
  • When modeling only causation, ensure the caused condition is represented in the supertypes and/or axioms
  • When modeling co-occurrence and causation, ensure both the causal and the caused conditions are represented in the supertypes and/or axioms

For a condition caused by a procedure

  • Ensure the caused condition is represented as a supertype and/or axiom
  • Ensure Disease (disorder) or the appropriate intermediate primitive is a supertype
  • Assign the procedure as the target of a Due to relationship

For a condition caused by an event

  • Ensure the caused condition is represented as a supertype and/or axiom
  • Assign the event as the target of a Due to relationship

For conditions that are causal, or causal and co-occurring, construct the FSN with due to 

  • X due to Y

For conditions specified as causal and temporal, construct the FSN with due to and the temporal relationship

  • For example,
    • X due to and following Y

Correct examples:

    • 735173007 | Shock due to anaphylaxis (disorder)|  is an example of a condition caused by a clinical finding/disorder.  Because the shock and the anaphylaxis are co-occurring, both conditions are represented in the supertypes and axioms, in addition to the Due to relationship.
    • 413532003 | Anemia due to blood loss (disorder)|  is an example of a condition caused by a clinical finding/disorder.  Because the bleeding could have been controlled and thus not necessarily present, only causation is modeled in this concept.  The blood loss/bleeding is not represented as a supertype. 

Incorrect examples not to be repeated:

    • Neutropenia associated with acquired immunodeficiency syndrome (disorder) - Do not use 'associated'; use only 'with' instead.  So, |Neutropenia with acquired immunodeficiency syndrome (disorder)|.
    • Dilated cardiomyopathy secondary to granuloma (disorder) - Do not use 'secondary to'; use 'due to' instead. So, |Dilated cardiomyopathy due to granuloma (disorder)|.

Determining causation only versus causation and co-occurrence

There are no heuristics to standardize the determination of a precoordinated combination modeled using only the Due to relationship versus modeling the Due to relationship in addition to representing the causative condition in the supertypes.  If both conditions must be present for the other to occur, both should be represented in the supertypes.  Whether both conditions must be present concurrently is determined by an understanding of the disease process.  Considerations include whether the conditions are chronic diseases, as these types of conditions will be ever present and thus require representation in the supertypes.  If the causing condition resolves but the resultant condition can remain, then representation of both conditions in the supertypes is unwarranted. 

There are approximately 425 legacy concepts with 'co-occurrent and due to'  in the description.  Do not add new concepts with the terming 'co-occurrent and due to', instead use co-occurrence modeling (both conditions are represented in a supertype) in addition to the Due to (attribute) if warranted by the clinical condition. 




Causation 2

Causation 2 is when 1the cause is a material entity, and 2the means of exposure/introduction are not significant. 

  1. A material entity refers to a concept within the Substance, Physical object, Pharmaceutical/biologic product, Physical force, and Organism hierarchies. 
  2. If the means of exposure/introduction are significant, then the causal factor is represented by a concept from the Event hierarchy, and the concept is modeled as Causation 1.

Modeling pattern

Naming pattern

Assign the caused disorder (X) as a supertype, or ensure that the caused disorder is a supertype following classification

Assign the causal factor (Y) as the value of a Causative agent (attribute)

X caused by Y


Correct example:

Incorrect examples not to be repeated:

    • Choking due to airway obstruction (finding)
    • Coma associated with diabetes mellitus (disorder)
    • Laser-induced burn (disorder)



Temporal sequencing without causation

Modeling pattern

Naming pattern

Assign the condition or procedure that occurred first in the patient as the target of an After (attribute) relationship.  Assign the condition that occurred second as a supertype (or ensure its presence in the ancestor tree).

Examples:

  • 402490007 |Calcinosis following localized fat necrosis (disorder)|

The fat necrosis occurred first in the patient, so this concept will have an After (attribute) with a value of Fat necrosis (disorder).  The calcinosis occurred secondarily, and thus Calcinosis (disorder) is a supertype of this concept. 

  • 16055031000119100 |Astigmatism of right eye following operative procedure (disorder)|

The operative procedure occurred first in the patient, so this concept will have an After (attribute) with a value of Surgical procedure (procedure).  The astigmatism occurred secondarily, so Astigmatism (disorder) is a supertype of this concept.  

Where X occurs after Y:

  • if it is not specified that X is due to Y (although causality is frequently implied), construct the FSN as X following Y


Caution against combination

Not all disorders occurring in combination should be precoordinated into a single concept.  Multiple clinical conditions should not be precoordinated in order to facilitate convenient recording in the medical record, even if the two conditions are often reported together.

For example,

  • The clinical conditions gastroenteritis and dehydration often occur in combination but require separate resolution, and therefore, are best recorded separately in the medical record as 25374005 |Gastroenteritis (disorder)| and 34095006 |Dehydration (disorder)|. 

Associated with (attribute)

In general, 47429007 |Associated with (attribute)| should be avoided due to the ambiguity which it conveys and the difficulty in applying this role consistently.  Instead, Due to is used when there is a direct causal relationship between the conditions; otherwise, the clinical conditions should be recorded as separate concepts in the medical record. 

There are a couple of exceptions when the use of 47429007 |Associated with (attribute)| is appropriate:

  1. General grouping concepts which aggregate more specific associations

    e.g. 6211002 |Polyarthritis associated with another disorder (disorder)| subsumes two children

    201972000 |Allergic arthritis of multiple sites (disorder)| modeled with 42752001 |Due to (attribute)| of 419076005 |Allergic reaction (disorder)|

    422565003 |Post-infective polyarthritis (disorder)| modeled with 255234002 |After (attribute)| of 40733004 |Infectious disease (disorder)|

  2. Device infections, i.e an infection of the tissue surrounding an implanted or inserted device, not due to the device itself.
    • Associated with is used to associate the device with the infection.
  3. Intolerance to substances, i.e the propensity of an adverse reaction to a substance to occur (other than hypersensitivity or allergic or non-allergic hypersensitivity). 
  4. There is no intolerance process that serves as the value for Has realization.
      • Associated with is used to associate the intolerance to the substance.

When to use "caused by" and when to use "due to"

Is cause a disorder or material entity?

It must be determined if a disorder is caused either by another disorder or by a material entity. A material entity is a concept found in Substance, Physical object, Pharmaceutical/biologic product, Physical force, or Organism subhierarchies. These subhierarchies are the current range constraints for the Causative agent (attribute) in the Clinical finding domain.  For combined disorders where a cause can be either a disorder (eg, alcoholism) or a material entity (eg, alcohol): 

Model as due to disorder if it is the indirect cause.

For example,

      • Megaloblastic anemia due to alcoholism (disorder)

Model as caused by material entity if it is the direct cause.

For example,

      • Inflammation of pancreas caused by alcohol (disorder)

Is cause a disorder or infectious organism?

In modeling concepts related to infectious diseases, a number of considerations need to be taken in to account.

  1. When the disorder is an infectious disease itself, and the organism is specified, then the concept will be modeled with 
    • |Causative agent (attribute)| with the specified organism 
    • |Pathological process (attribute)| with the type of infectious process

      2.  Disorders can be modeled with |Due to|, with |After|, or with both |Due to| and |After| relationships to infectious diseases.  If the focus disorder is itself an infectious disorder, it will also have a |Causative agent| relationship when the organism is specified.

For example,

|Causative agent| relationship: 721742004 |Otitis media caused by Streptococcus pneumoniae (disorder)|
  
|Due to| relationship: 698733009 |Intestinal obstruction due to tuberculosis (disorder)|
 
|Due to| and |Causative agent| relationship: 866044006 |Mycosis due to human immunodeficiency virus infection (disorder)|
  
|After| relationship: 182961000119101 |Acute disseminated encephalomyelitis following infectious disease (disorder)|
  
|After| and |Causative agent| relationship: 4740000 |Herpes zoster (disorder)|
  
|Due to| and |After| relationship: 1148594002 |Chronic arthritis due to and following rheumatic fever (disorder)|

Applying the |Due to|, |After|, or both |Due to| and |After| relationships to a concept will not lead to it being a subtype of |Infectious disease (disorder)| unless it is itself an infectious disease.

Generally, when |Causative agent| is used in the concept's modeling, the terming 'caused by' is used in the FSN.  Similarly, when |Due to| is used in the concept's modeling, the terming 'due to' is used in the FSN.  In some situations, both the |Causative agent| and |Due to| are used in a concept's model, and so the naming may vary based on the situation. 

In some cases, the DUE TO takes precedence because of a relationship between the causative agent and the DUE TO disorder.

For example, 

288021000119107 |Disorder due to alcohol abuse (disorder)|

 

Figure 1: Stated form of |Disorder due to alcohol abuse (disorder)|

In other cases, the DUE TO relationship is used as a means to classify the concept appropriately while the CAUSATIVE AGENT takes precedence.

For example,

1251395000 |Injury of skin caused by class Anthozoa (disorder)|

Figure 2: Inferred form of |Injury of skin caused by class Anthozoa (disorder)|

In this case, the DUE TO represents the "injury" part of the concept and allows classification as a traumatic injury. An alternative, but less appealing FSN would have been "Disorder of skin due to traumatic injury caused by class Anthoza". So, if the concept FSN specifies a disorder causally associated with another disorder, then use "due to" in the FSN; if the FSN specifies a disorder causally associated with an "agent" (organism, physical object, substance, etc.), then use "caused by" in the FSN. 



Exception to naming convention for combined disorders

Exceptions may exist to the above guidance which requires review on a case-by-case basis.

The FSN submitted by a requestor may be used as preferred term even if it does not comply with the above recommended pattern.  However, do not use phrases such as secondary to, as a result of, etc. in lieu of due to.  

Rather than the naming conventions described above, use the names that are accepted clinical parlance and that represent specific pathophysiologic entities for some combined disorders, as the preferred term.  

The stricter rules for FSN construction do not prevent the addition of more familiar connectives in other descriptions, for example with, or associated with.


Disorder combination modeling

  • Covers combinations of only two disorders. However, combinations often include more than two disorders (for example, syndromes).  Document multiple conditions in a single statement only for syndromes or strong associations based on a common predisposing factor.
  • Does not cover absent components or negation
  • Does not cover cases where combination concepts are demonstrably classification-derived (This limitation accepts that some content may be so obviously based on a class or category in a classification that it would be undesirable to reinterpret its semantics.)
  • The modeling approach may be difficult to apply in all cases of combined disorders; domain-specific templates should be developed to ensure modeling consistency and accuracy. 




(See also, Appendix, Concept Models: Disorder Combinations)

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