Doctors, hospitals, insurers and some patients are bracing for possible disruptions on Oct. 1 when the U.S. health-care system switches to a massive new set of diagnostic codes for describing illnesses and injuries.

The Wall Street Journal reports the new system of codes doctors must use to get paid is expanding from 14,000 to 70,000.

The latest version of the so-called International Classification of Diseases (ICD-10) also expands a separate set procedure codes for hospitals from 4,000 to 72,000.

Under the new system, cardiologists will 845 codes for angioplasty, dermatologists will need to specify which of eight kinds of acne a patient has, and gastroenterologists must enter a separate code for each possible cause of a patient’s stomachache.

Hospitals and physician practices have spent billions of dollars on training programs for the diagnostic code update, which has been postponed three times since 2011.

Some experts predict the implementation of the new codes could disrupt the healthcare system. But others suggest the transition shouldn’t be too taxing for doctors, hospitals, insurance companies or patients.

“We’re hoping it will be like Y2K,” when the switch to 2000 dates was expected to crash computers world-wide, said Robert Wergin, president of the American Academy of Family Physicians, to the Journal. “Everybody will worry, and the claims will go through fine.”