Healthcare providers currently use a list of more than 18,000 diagnosis codes, known as International Classification of Diseases, 9th Edition (ICD-9), to bill Medicare and Medicaid. Next year, the number of codes will expand to more than 140,000, with the goal that more specific diagnoses will lead to better tracking of healthcare trends and cut down on fraud. The sheer size of ICD-9 makes it a minefield for some providers and suppliers submitting claims for payment and a potential goldmine for others. The U.S. fee-for-service model, where providers are paid by procedure, has lent itself to a type of fraud known as "upcoding," officials say. Providers use the higher-fee codes to charge the government for lower-fee procedures or, in some cases, services not rendered at all.