Representing Units of Measure (For Use with Numerical References and Values)

Type	Standard / Implementation Specification	Standards Process Maturity	Implementation Maturity	Adoption Level	Federally required	Cost	Test Tool Availability
Standard	The Unified Code for Units of Measure	Final	Production		Yes	Free	Yes Yes

Limitations, Dependencies, and Preconditions for Consideration	Applicable Value Set(s) and Starter Set(s)
UCUM is a syntax for representing units of measure for use with numerical references and values. It is not an enumerated set of codes. The case sensitive version is the correct unit string to be used for interoperability purposes. Per public comments received, there may be some limitations with UCUM in the laboratory domain that remain unresolved. The abbreviations used for a few of the units of measure listed in the UCUM standard are currently on lists of prohibited abbreviations from the Institute for Safe Medication Practice (ISMP). Some abbreviations for units of measure include symbols which may be in conflict with other HL7 standards. Some abbreviations for units are nonstandard for human understanding.(For example, if a result for a White Blood Cell count is 9.6 x 103/μL, the UCUM recommendation for rendering this value in a legacy character application is 9.6 x 103/uL. Because the “” is a symbol for multiplication in some systems.) This recommendation may result in errors either by the information system or the human reading the result. Some abbreviations used in UCUM are not industry standard for the tests that use these units of measure.	Units Of Measure Case Sensitive 2.16.840.1.113883.1.11.12839 (most frequently used codes) “Table of Example UCUM Codes for Electronic Messaging" published by the Regenstrief Institute, Inc. Value set is made available at http://loinc.org/usage/units and identified by the OID 1.3.6.1.4.1.12009.10.3.1

Limitations, Dependencies, and Preconditions for Consideration

Applicable Value Set(s) and Starter Set(s)

UCUM is a syntax for representing units of measure for use with numerical references and values. It is not an enumerated set of codes.
The case sensitive version is the correct unit string to be used for interoperability purposes.
Per public comments received, there may be some limitations with UCUM in the laboratory domain that remain unresolved.
The abbreviations used for a few of the units of measure listed in the UCUM standard are currently on lists of prohibited abbreviations from the Institute for Safe Medication Practice (ISMP).
Some abbreviations for units of measure include symbols which may be in conflict with other HL7 standards.
Some abbreviations for units are nonstandard for human understanding.(For example, if a result for a White Blood Cell count is 9.6 x 103/μL, the UCUM recommendation for rendering this value in a legacy character application is 9.6 x 10*3/uL. Because the “*” is a symbol for multiplication in some systems.) This recommendation may result in errors either by the information system or the human reading the result.
Some abbreviations used in UCUM are not industry standard for the tests that use these units of measure.

Units Of Measure Case Sensitive 2.16.840.1.113883.1.11.12839 (most frequently used codes)
“Table of Example UCUM Codes for Electronic Messaging" published by the Regenstrief Institute, Inc. Value set is made available at http://loinc.org/usage/units and identified by the OID 1.3.6.1.4.1.12009.10.3.1

Comment

Submitted by cmcdonald on 2018-10-01

This safe medical practice…

This safe medical practice as defined in the context of prescribing. Not reporting of numeric results, so the objection is not relevant.

The "^" value could be a problem. It's in V2 but it's not the only way to represent powers. Will ask the UCUM committee to address V3 CDA and FHIR so there aren't delimiters to conflict with.

UCUM should be considered the code in triumvirate of code display text and code system. Senders are free to deliver whatever display text they now send.

Point out industry standards. The problem in observation messages is that they are totally understandardized.

Submitted by cmcdonald on 2018-10-01

Strongly support UCUM use so…

Strongly support UCUM use so results can be accurately analyzed.

Submitted by dvreeman on 2017-11-20

We strongly concur with the…

We strongly concur with the listing of UCUM here. Daniel Vreeman has compiled a list of UCUM conversion and validation resources here. It is worth noting that UCUM is designed for accomplishing a computable units representation in electronic communication. This is the main interoperability need. Having display strings for humans (whether patients, providers, or others) is another matter. We recommend that the last bullet point (Numerical representation are uniform…) be removed as it totally unclear.

Submitted by kwboone on 2017-11-20

Table 3: Dimensionless units…

Table 3: Dimensionless units. The units ppb and ppt are deprecated because the names “billion” and “trillion” are ambiguous. The expression “10*-9” or “10*-12” should be used instead. When the units percent or “parts per N” are used for concentrations specific units are prefered, e.g., “ug/l” for mass concentration. The expression “ug/kg” for ppb is also valid.
the number ten for arbitrary powers	10n	10*	10*	no	10	1
the number ten for arbitrary powers	10n	10^	10^	no	10	1

Both * and ^ can be used for arbitrary powers as shown in the table above (see http://unitsofmeasure.org/ucum.html#section-Derived-Unit-Atoms)

Recognize a value set that uses the ^ form.

WHICH values in HL7 conflict? I know SOME values are different, but I have seen none that conflic. See http://motorcycleguy.blogspot.com/2009/11/iso-to-ucum-mapping-table.html

Submitted by cmcdonald on 2018-10-01

Good point. Will explore…

Good point. Will explore with users.

Submitted by vojtech_huser on 2017-10-31

Test tool

UCUM validators exist. Ability to test if unit is valid or unit1 converts to unit2 are all valid test tasks. Consider changing n/a in testing to linking to validation and conversion tools.

e.g.,

http://xml4pharmaserver.com/WebServices/UCUM_webservices.html

https://lhncbc.github.io/ucum-lhc/demo.html

Submitted by Brett Andriesen on 2017-11-06

Thank you for this comment…

Thank you for this comment. Links to these test tools have been added.