To re-examine the validity of the medical knowledge that are embedded in the legacy system, we translated a Medical Logic Module (MLM) for hyperkalemia patient screening into the GuideLine Interchange Format (GLIF). We used a set of guiding principles to direct the translation. In addition, we used the GLIF3 Guideline Execution Engine (GLEE) as a testing tool to validate the encoded GLIF guideline by applying it to 5 simulated patient cases. The result has shown that it is possible to translate Arden MLMs into GLIF guidelines. However, significant efforts are necessary to handle the problems arose during the translation process. Automatic translation could be a more generalizable approach for future work.