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Units of Measure in Clinical Information Systems

Regenstrief Institute for Health Care and Indiana University, Indianapolis, Indiana (GS, CJM, JGS); Benjamin Franklin University Hospital (UF) and Freie Universität (UF, TT), Berlin, Germany.

Correspondence and reprints: Gunther Schadow, MD, Regenstrief Institute for Health Care, 1001 West 10th Street, RHC 5th Floor, Indianapolis, IN 46202-2859;e-mail: <schadow g{at}regenstrief.iupui.edu>.

Received for publication: 07/27/98; accepted for publication: 11/13/98.

The authors surveyed existing standard codes for units of measures, such as ISO 2955, ANSI x3.50, and Health Level 7's ISO+. Because these standards specify only the character representation of units, the authors developed a semantic model for units based on dimensional analysis. Through this model, conversion between units and calculations with dimensioned quantities become as simple as calculating with numbers. All atomic symbols for prefixes and units are defined in one small table. Huge permutated conversion tables are not required. This method is also simple enough to be widely implementable in today's information systems. To promote the application of the method the authors provide an open-source implementation of this method in JAVA. All existing code standards for units, however, are incomplete for practical use and require substantial changes to correct their many ambiguities. The authors therefore developed a code for units that is much more complete and free from ambiguities.