Final answer:
Code 99203 is used for a new patient with an expanded history, an expanded exam, and straightforward medical decision-making for a problem or condition that is low to moderate, and an average visit time of 20 minutes.
Step-by-step explanation:
The code used for a new patient with an expanded history, expanded exam, and straightforward medical decision-making for a problem or condition that is low to moderate in nature, with an average time of 20 minutes, would be 99203. This code is part of the Evaluation and Management (E/M) codes that are used in medical billing to categorize the type and complexity of a patient's visit. The CPT codes (Current Procedural Terminology codes) provide a uniform language that accurately describes medical, surgical, and diagnostic services, thereby ensuring reliable communication among providers, patients, and payers.