In ICD-10 coding, what can the third character be and where is the decimal placed?

• A. It can be alpha or numeric, and a decimal is placed after the third character.
• B. It must always be numeric and a decimal is placed after the fourth character.
• C. It can be numeric only and no decimal is used.
• D. It is alphanumeric and the decimal is placed after the second character.

Answer: (A)

Understanding how ICD-10-CM diagnosis codes are built helps you code with precision. The code starts with a three-character category. The third character in that category can be either numeric or alphabetic, depending on the specific category. The decimal point is placed immediately after that third character, creating a separation between the basic category and the more detailed subcategory that follows. Those additional characters after the decimal provide further specificity and can be numeric or alphanumeric as required by the code. This structure is what lets ICD-10-CM convey nuanced diagnoses in a standardized way.