From erroneous medical bills to denied health services, Americans may need patience grappling with insurance claims beginning today, the much-anticipated launch of tens of thousands of new government-mandated “ICD-10” codes used to describe diseases and hospital procedures in the billing process.

At least one analysis says one in four of the nation’s doctor practices aren’t ready for the transition to International Classification of Diseases, Tenth Revision, known as “ICD-10.” After two years of delays, medical care providers have to be ready for the conversion to 140,000 new codes that they will use in order to bill government and private insurers.

Health insurance companies, employers and their human resources departments have been working with patients and health plan enrollees, warning of potential problems. Aon Hewitt (AON ), a large employee benefits consultancy, says there is potential for doctors and hospitals to use outdated codes and potentially bill patients for services that could be covered. View full story here