This field contains the format of the observation value in OBX. It must be valued
if OBX-11-Observ result status is not valued with an "X". If the value is CE then
the result must be a coded entry. When the value type is TX or FT then the results
are bulk text. The valid values for the value type of an observation are listed in
HL7 Table 0125 - Value Type.
The observation value must be represented according to the format for the data type
defined in Chapter 2, Section 2.9, “Data Types.” For example, a PN consists of 6 components,
separated by component delimiters.
Although NM is a valid type, observations which are usually reported as numbers will
sometimes have the string (ST) data type because non-numeric characters are often
reported as part of the result, e.g., >300 to indicate the result was off-scale for
the instrument. In the example, ">300", ">" is a symbol and the digits are considered
a numeric value. However, this usage of the ST type should be discouraged since the
SN (structured numeric) data type now accommodates such reporting and, in addition,
permits the receiving system to interpret the magnitude.
All HL7 data types are valid, and are included in Table 0125 except CM, CQ, SI, and
ID. For a CM definition to have meaning, the specifics about the CM must be included
in the field definition. OBX-5-observation value is a general field definition that
is influenced by the data type OBX-3, so CMs are undefined in this context. CQ is
invalid because units for OBX-5-observation value are always specified explicitly
in an OBX segment with OBX-6 units. SI is invalid because it only applied to HL7 message
segments, and ID because it requires a constant field definition.
The RP value (reference pointer) must be used if the actual observation value is not
sent in OBX but exists somewhere else. For example, if the observation consists of
an image (document or medical), the image itself cannot be sent in OBX. The sending
system may in that case opt to send a reference pointer. The receiving system can
use this reference pointer whenever it needs access to the actual image through other
interface standards, e.g., DICOM, or through appropriate data base servers.
The full definition of these data types is given in Chapter 2, Section 2.9, “Data
Types.” The structured numeric (SN) data type, new to version 2.3, provides for reporting
ranges (e.g., 3-5 or 10-20), titres (e.g., 1:10), and out-of-range indicators (e.g.,
>50) in a structured and computer interpretable way.
We allow the FT data type in the OBX segment but its use is discouraged. Formatted
text usually implies a meaningful structure e.g., a list of three independent diagnoses
reported on different lines. But ideally, the structure in three independent diagnostic
statements would be reported as three separate OBX segments.
TX should not be used except to send large amounts of text. In the TX data type,
the repeat delimiter can only be used to identify paragraph breaks. Use ST to send
short, and possibly encodable, text strings.
CDA documents are to be exchanged in the OBX segment in any message that can exchange
documents (such as MDM or ORU). Within the OBX segment, the MIME package is encoded
as an encapsulated (ED) data type.
Template OBX - Observation/Result
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