The International Classification of Diseases, Ninth Revision (ICD-9) is nearly forty years old and doesn’t reflect modern medicine. It even lacks the capacity to cover new treatments and technology and fails to provide a significant level of detail in diagnoses, the nature and extent of a complication and specificity regarding how a complication is treated.

The International Classification of Diseases, Tenth Revision (ICD-10) provides more accurate medical descriptions and captures data needed to track changes in modern health care—changes that will make public health surveillance better equipped to monitor epidemiology. More precise codes have benefits in claims processing, as more accurate payments would mean fewer rejected or fraudulent claims.

The compliance date for providers to transition to the greatly expanded ICD-10 is October 1, 2015. All ICD-9 codes used in transactions for services or discharges on or after the compliance date will be rejected as non-compliant and the transactions will not be processed, meaning that providers may face serious disruptions to cash flows if they are not ready.

Much of the developed world made the switch to ICD-10 years ago, and while many providers insist that ICD-10 is long overdue in the U.S., there is concern over implementation. Delays in implementation have wasted time and money as uncertainty has forced the industry to retain fully functional systems in both ICD-9 and ICD-10. Kristi Matus, Chief Financial and Administrative Officer of Athena Health, told Congress to either “pull the trigger or pull the plug” on ICD-10, since another delay would bring additional significant costs for health plans and providers that have been, or will be, ready to implement the system this year. While many large providers have indicated that they are ready for the transition, smaller providers are concerned with associated costs.

Costs will vary for providers based on a number of things including whether a practice must pay the cost of upgrading their own systems or a practice has contracts with vendors responsible for the upgrades. The Centers for Medicare and Medicaid Services (CMS) has estimated that “in early stages of implementation, denial rates will rise by 100 to 200 percent, and that days in accounts receivable will grow 20 to 40 percent.” According to Athena Health, “That’s because the migration to ICD-10 carries a risk due to incomplete or inaccurate translation of existing policies, benefits, and payment rules within payer systems.”

Smaller practices may be disproportionately affected in their ability to manage delays in payments as a result of having less time and resources. The burden of ICD-10 could force physicians to reduce the number of patients they see, making it more difficult for patients to get the care they need. Physicians may retire early or be forced to close their business if they don’t have the funds necessary to implement the system.

ICD-10 must be implemented, and further delays could result in billions more lost in the health care industry. ICD-10 would significantly improve efficiency in the health care system, support better reimbursement models and provide better data for epidemiological purposes, but as an unfunded mandate without an appropriate implementation plan, it may represent a threat to smaller practices or physicians in rural areas.