O4.1. Observation - Semantic content

The primary semantic content of each statement is represented by the code and value attributes. The code attribute is always a coded concept descriptor, the value may be a numeric value or range with units, a coded concept descriptor or another type of data appropriate to the specified observation.

[1..1] code (CD) {CWE:EhrObservationCode}
A code specifying a the nature of the observation.
  • The code is taken from a clinical coding scheme approved for use in the realms in which the message is used.
  • This will be a code or concept identifier from the Read Codes, CTV3 and in future SNOMED CT.

Notes

  • This code may represent the full semantics of some qualitative observations (i.e. encapsulating both the nature of the observation and the finding). Thus the Read Code for "Diabetes melitus" is conveyed in this attribute and by default the value field is absent.
  • However, if the value field is present it significantly affects the interpretation (as detailed in the description of the value field) and must not be ignored.

Note on qualifiers and modifiers

Note that the intended usage of the "qualifier" element within the CD datatype is for qualification or refinement of the code not for "major modification" of meaning. Thus it must only be used where the meaning of the combined expression is a logical subtype of the meaning of the code.

[0..1] uncertaintyCode (CV {CNE:ActUncertainty} )
Indicates whether the author has explicitly asserted some uncertainty in an observation..
[0..1] value (ANY)
The result value of an observation action. The following are the approved uses of the ANY datatype:.
  • Quantitative measurement
    PQ ::Physical quantity (real number with unit.)
  • Titre (e.g., 1:64) and other ratios
    RTO :: A ratio of two integer numbers.
  • Ranges (e.g., < 3; 12-20)
    IVL<PQ>  :: Interval of physical quantity.
  • Ordinals (e.g., stage "IIa","++") 
    ST  a string*.
  • Index (number without unit)
    PQ with a dimensionless unit (e.g., "1" or "%").
  • Nominal results (e.g. description)
    ST a string
  • Results expressed in fixed font text (as used for microbiology in the NHS PMIP messages to produce text tables representing outcome of a microbiology culture) are expressed as the Encapsulated Data Text and Line Breaks flavour of the ED datatype.

Note*

  • HL7v3 specifications indicate that codes should be used for Ordinal and Nominal results. However, such codes do not exist and the string data type is preferred to a fabricated code.