ICD-10 chapters and code letters

I’ve been thinking about ICD-10 codes; they come up a lot in my work. The ICD-10-CM standard is divided into 21 chapters, which generally correspond to the first letter of a code. However, a chapter may contain blocks beginning with more than one letter, and codes starting with a single letter, namely D, can span two chapters. Here’s a diagram I made to visualize the relationship between chapters and initial letters of codes. Notice there’s no letter U on the diagram. That’s because U is reserved for special/provisional codes. Related posts Rare and strange ICD-10 codes Regex to match ICD-9 and ICD-10 codes New ICD-10 code weirdness The post ICD-10 chapters and code letters first appeared on John D. Cook.