Arden Syntax

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The Arden syntax was conceptualized in 1989 by a group of medical informaticians. The goal of the group was to develop a standard for sharing medical knowledge by writing medical clinical decision support rules (1). In 1992 Arden syntax was approved as a standard by the American Society of Testing and Machinery (ASTM) and in 1999, Health Language 7 (HL7) produced the second version which is backward compatible (2). In 2002 the Arden syntax became an American National Standards Institute (ANSI) approved standard.

In Arden syntax each decision rule is called a medical logic module (MLM) (3). A MLM can be stored in ASCII format and written by any text editor. The Arden syntax was designed to be used with any proprietary clinical decision support system (CDS). Arden syntax MLMs have been used to generate alerts and reminders, administrative support and diagnoses. In CDS systems an event or a change to a patient record gets coded which triggers at least one or more evoking MLMs based upon a condition the MLM is designed to support (4).

The Arden syntax MLM has three parts: maintenance, library and knowledge. The MLMs are intended to be written and maintained by healthcare providers with limited programming experience or background. An example of a MLM can be viewed at the health informatics wiki (5).

One important limitation to implementing Arden syntax is lack of structured, coded data in databases in CDS systems. The minimum amount of data that needs to be collected includes patient demographics, laboratory results and medication. Also developing knowledge rules is a slow process and rules downloaded from internet sites or shared from other institutions must be validated for local use. Knowledge also needs to be kept current, shared and maintained between different organizations.


  1. Karadimas HC, et al. Arden/J: An Architecture for MLM Execution on Java Platform, JAMIA. 2002;9:359-368.
  2. Health Level Seven. Arden Syntax for Medical Logic Systems, 1999. [1]
  3. Shortliffe EH, Cimino JJ. Biomedical Informatics: Computer Applications in Health Care and Biomedicine.(2006)3rd ed. Springer.
  4. Van de Velde R, Degoulet. Clinical Information Systems: A Component-Based Approach.(2002). Springer.
  5. [2]

Submitted by Cassius Lockett