Question: Are there any ICD-10 guidelines for when to use a code that is specific to a pediatric patient and when to an adult? For example, the well-check encounter codes provide different codes for newborns, infants/children, and adults. I know that ICD-10 defines a newborn as a child under the age of 28 days, but what is the cutoff between a child and an adult? Alabama Subscriber Answer: According to AHA ICD-10-CM Coding Clinic, “there are no official guidelines or coding instructions (except in a few specific codes like the pediatric body mass index codes) that distinguish pediatric from adult diagnoses. This is a payer edit issue; therefore, contact the specific payer to determine what, if any, age edit applies” (2017 Vol. 4, No. 4). So, in the example you provide — the well-check codes — ICD-10 does not tell you at what age you should apply Z00.12- (Encounter for routine child health examination) or Z00.0- (Encounter for general adult medical examination) to preventive medicine encounters. But a payer will have guidelines that you should follow before you use one or the other. For example, these codes are subject to age-specific Medicare Code Edits (MCEs), which instruct you that Medicare will reimburse for a Z00.12- code only for patients from the age of 0 through 17 years old, and a Z00.0- code for patients older than 18 years of age.