Unified Code for Units of Measure (UCUM) is a system for coding units of measure. The coding system was developed with the aim of representing all units of measurement used internationally in science, including laboratory medicine and pharmaceuticals. The codes themselves represent units according to a defined notation, which is he prerequisite that quantitative data and other numerical values can be unambiguously exchanged. Since 1999, UCUM has been maintained and published in English by the Regenstrief Institute. The BfArM provides a value list with UCUM codes and descriptions of the codes for use in health applications in Germany with german translations.

Area of application of UCUM

Quantitative data can be exchanged in a standardized and automated way in IT applications for medical documentation with the help of UCUM. The use of a standard can improve the clarity of interpretation of quantitative values. This is applied, among other things, when mapping measurement results from laboratory tests or clinical examinations. Due to the international use of UCUM, worldwide interoperability is possible.

Scope of UCUM

UCUM codes are composed of units, prefixes and syntax elements based on rules. The rule system is described in the UCUM specification of the Regenstrief Institute. UCUM codes can therefore be generated according to the specification as required. New symbols can be applied for at to the Regenstrief Institute for UCUM.

Regenstrief Institute specification for UCUM version 2.1
Submission of change requests for UCUM to the Regenstrief Institute

The basis of the symbols for units and mathematical operators is the ASCII-7 character set. The notation for UCUM codes can be generally described by the following:

• All individual units are mapped with the usual unit symbol.
  Examples: "g" for gram, "Hz" for hertz, "d" for day.
• Mathematical operators for multiplication and division can be used: "." as multiplication sign, "/" as multiplication sign, "*" as exponent sign. Examples: "/10*3" for "per thousand", "g/h" for grams per hour.
• Prefixes for units are adnexed to a unit without a separator. Examples: "ng" for nanogram, "mm" for millimeter.
• Units whose names are made up of several words are joined together with square brackets. Information that affects the meaning of the size dimension is also shown in square brackets.
  Example: "[ppm]" for part per million, mm[Hg] for millimeters of mercury column (an indication of pressure).
• Multiple units or numerical values forming a mathematical product are described with round brackets if the term is in the denominator of a fraction: "mL/(24.h)" for milliliters per 24 hours, dyn.s/(cm.m²) for dynsecond(s) per centimeter and square meter
• There are other elements in UCUM that stand for enumerations, dimensionless values or a simple description. These are used in UCUM as "annotations" and are represented in the code with curly brackets. Semantically, annotations are equivalent to the number "1".
  Examples: g/mol{creatinine}, mg/g{tissue}, %{index}, {genome}/mL

The Regenstrief Institute publishes a sample list of common units used internationally (about 850 entries).

"Common UCUM units" of the Regenstrief Institute Version 1.5

Use in Germany

In Germany, UCUM is used in information models such as MIO Laborbefund (MIO Laboratory Report) and MIO Basisprofile (MIO Basic Profiles). Usually, laboratory tests are coded with LOINC and quantitative results with UCUM.

Information on the MIO laboratory Report from mio42 GmbH/KBV
Information about the MIO Basic Profiles of mio42 GmbH/KBV

The exchange of health data for legal purposes in Germany is based on the list of "Common UCUM Units".

UCUM is also used for data exchange in Europe as a standard for the exchange of data according to § 219d SGB V.

Together with the KKG AG LOINC, the requirements for UCUM for the exchange in Germany are being developed. The BfArM adapts and extends the list of common UCUM units according to the requirements. In the adapted list, the natural language description of the units is translated. In addition, an abbreviated display name is introduced for unambiguous interpretation of the code. This is based on the UCUM code and consists of a slightly modified notation.

Download of the UCUM value list for legal applications in Germany

The notation chosen for the UCUM code has been slightly adapted to the way units are usually notated in Germany. The addition of a display name to the list of common UCUM units is intended to support laboratory and clinical use. The following adaptations were made for the display name:

• The caret character is used as exponent character for numbers (^).
• The exponents of the units are displayed as superscript units.
• The symbols used in the laboratory and clinic were used for the display: "µ" instead of "u" for the prefix "Micro", "°C" instead of "Cel".
• "l" for liter was written in lower case.
• The annotations have been translated into german.

If you would like to request changes for application purposes in Germany, please send them to loinc@bfarm.de.