The Arden Syntax for Medical Logic Modules (MLMs) is a standard adopted by American Society for Testing and Materials (ASTM) (in the Summer of 1998 it is moved to Health Level Seven (HL7)) to represent modular medical logic.

The general structure of the Arden Syntax are slots within three categories, maintenance, library and knowledge. Within each slot, different representation formalisms are taken. For example, in logic slot of knowledge category, if-then rules is used to represent the logic of the MLM invoked, while in purpose slot of library category, text is used to represent the purpose of the MLM. Here is an example of MLM in Arden Syntax:

maintenance:
title:
CT study with contrast in patient with renal failure;;
filename:
astm_ct_contrast;;
version:
1.00;;
institution:
ASTM E31.15; SMS;;
author:
Harm Scherpbier, M.D.;;
specialist:
;;
date:
1995-09-11;;
validation:
testing;;
library:
purpose:
Issue alert when physician orders CT study with contrast in patient with renal failure;;
explanation:
If physician orders CT scan with contrast, this rule retrieves most recent serum creatinine.  If the value is less than 1 week old, and more than 1.5, the system issues an alert to the physician to consider the possibility that his patient has renal failure, and to use other contrast dyes.;;
keywords:
;;
citations:
;;
links:
;;
knowledge:
type:
data_driven;;
data:
last_creat := read last {"Creatinine level"};
last_BUN := read last {"BUN level"};
;;
evoke:
ct_contrast_order;;
logic:
if
last_creat is null and last_BUN is null
then
alert_text := "No recent serum creatinine available.  Consider patient's kidney function before ordering contrast studies.";
conclude true;
elseif
last_creat > 1.5 or last_BUN > 30
then
alert_text := "Consider impaired kidney function when ordering contrast studies for this patient.";
conclude true;
else
conclude false;
endif;
;;
action:
write alert_text || "\nLast creatinine: " || last_creat || " on: " || time of last_creat || "\nLast BUN: " || last_BUN || " on: " || time of last_BUN;
;;
urgency:
50;;
end: