Analysis of clinical specimens to obtain information about the health of a patient.

Data Element

Result Unit of Measure

Unit of measurement to report quantitative laboratory test results.

Applicable Vocabulary Standard(s)

Applicable Standards
  • The Unified Code of Units for Measure, Revision 2.1


ACLA Comment on the Result Unit of Measure for USCDI v5

The American Clinical Laboratory Association (ACLA) comments pertain to the burden of using the Unified Code for Units of Measure (UCUM).

ACLA believes the vocabulary standard, UCUM, should be recommended, but not required. Laboratories should be allowed to use units of measure other than UCUM. The unit of measure provided by the instrument manufacturers, including FDA authorized, cleared, or approved method, is the standard that laboratories need to adhere to for result reporting. We recommend conversations and adoption from instrument manufacturers is incumbent for the adoption of UCUM to be viable. We would also recommend the ONC solicit feedback from CAP and CLIA on their stance on the need for conversion to UCUM.

The UCUM can be a preferred standard, but it should not be required for all tests. Currently, there is a large base of units of measure that are in use across trading partners. To convert these units to UCUM would be problematic, difficult to achieve and time consuming.

While ACLA acknowledges UCUM as an option for standardized vocabulary for units of measure it is crucial to recognize and understand the limitations of the UCUM coding system and the impact of key issues identified by ACLA prior to universal adoption.

  • UCUM has codes for ALL US customary units (e.g., UCUM guide §35 U.S. survey lengths, and §37 U.S. volumes). However, these will not necessarily have the same string representation that a given laboratory uses (see UCUM GUIDE It also includes codes for all non-arbitrary unit of measure (UoM), includes many arbitrary UoM such as Somogyi units, and has a way to include strings (which will not be computable for any arbitrary units -- but arbitrary units are never computable in the sense that they can be interconverted).
  • There are issues with transmission of unusual or unrecognizable characters (e.g. ‘*’ or ‘^’, and descriptions sometimes use ‘#’ and ‘&’) which cause errors in some sending and receiving systems. These are restricted characters that cause issues in data exchanges including HL7.
  • Some recommended UCUM units exceed the HL7 prescribed field lengths for the coded element of 20 characters (e.g. nmol{BCE}/mmol{creat}, %{normal_pooled_plasma}). For example, some state public health systems are unable to accept more than 20 characters in the unit of measure HL7 field.
  • The mandate to report all units of measure in a UCUM format could impact patient safety. 
    • There may be a potential for discrepancies between the units of measure directed by instrument and/or reagent vendors in their package insert/operator’s manual for result reporting of a particular test vs. the UCUM units identified for that test. 
    • The instruments that process the specimens may or may not use UCUM standard units. There is a risk in converting results into a unit of measure that is different than the original unit of measure. 
      • Conversions cannot always be achieved to equivalency.
      • Even if it is accurately converted, it does not ensure that providers will always interpret it correctly.
      • It is common for conversion algorithms to encounter errors. While the problem with that is self-explanatory, a second issue may not be.  The value and the units of message occupy two separate HL7 fields.  Should a numeric value encounter an error, and the translation process choses to handle the issue by leaving the value as it was received but incorrectly modifies the units of measure (assuming the value algorithm performed correctly), there could be a disconnect between the value and units of measure that could greatly impact the interpretation of the results, and by extension, the health of the patient.
    • At present, units can be very confusing and unpredictable and almost impossible to use for computer purposes like decision support and quality assessment. We have seen more than 30 different representations of units for the number RBCs e.g.  10^12/Lit  bill/liter,  10*12/liter., etc.


Highly support and agree with this new data element. The Result Unit of Measure will ensure consistency across the healthcare ecosystem. For example, if a Blood Glucose Level was sent without the unit of measure, then the receiving organization may mis-categorize the result as normal or abnormal.

ACLA Comment on Laboratory: Result Unit of Measure

The American Clinical Laboratory Association (ACLA) pertains to the Applicable Standard(s): The Unified Code for Units of Measure (UCUM) \ and the estimate of Overall Burden: Very low burden. This element should already be part of the EHR due to its laboratory regulatory requirement (CLIA).

ACLA Comments:

These comments pertain to the burden using Unified Code for Units of Measure (UCUM).

Using only the UCUM as a standard is problematic and the burden would be very high using this standard. The UCUM cannot be used when it is not supported by the analytic procedure’s documentation for an FDA authorized, cleared, or approved method. Existing interfaces should not be required to update to UCUM. (Note: the FDA approved units must be used for reporting, regardless of the standard used). 



THIA Comment on Laboratory: Result Unit of Measure

The Texas Health Informatics Alliance (THIA) Policy and Standards Working Group supports the proposal for the result unit of measure; however, we recommend adopting the latest Unified Code for Units of Measure (UCUM) version, relative to when the policy gets adopted. The current proposal references UCUM v2.1, which was released in December 2017. The most up-to-date version is UCUM v2.9, which was released in May 2021.

CDC's Consolidated Comment for USCDI v4

  • Physicians, nurses, epidemiologists, and anyone who is using laboratory reports for patient care and public health, including patients, rely on access to the result unit of measure for the correct interpretation of the provided laboratory results. It must be available to the authorized person who ordered the test and, if applicable, the individual responsible for using the test results. It is required by CLIA for all laboratory reports, 493.1291(a)(6) Standard: Test report. Link: ""
  • Comments from NACCHO: NACCHO supports including the data element unit of measure. However, the unit measure should be standardized and recommends the HL7 standard for the unit of measure to be used. Without a unit of measure, the values/results would be uninterpretable as each lab may report units differently.

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