Final answer:
The HIPAA rule requiring standardized medical transactions and codes is known as the Transaction and Code Set Rule, aiming to simplify administration and reduce costs in healthcare.
Step-by-step explanation:
The rule in HIPAA that required nationally standardized medical transactions and codes is known as the Transaction and Code Set Rule. This mandate was a significant part of HIPAA's efforts to simplify the administration of healthcare by establishing a uniform standard for electronic data interchange (EDI) and ensuring the secure and efficient handling of healthcare information. By standardizing transactions, HIPAA aimed to reduce administrative costs and improve the quality of healthcare.