Pathology/Lab Coding Alert

Question: I’d been taught that ICD-10 diagnosis codes have three to seven characters, with the first digit an alpha character, followed by second, third and fourth characters that are numeric, and fifth, sixth or seventh characters that can be alpha or numeric. Then I saw a code — C7A.020 — for malignant carcinoid tumor of appendix. Is that correct, and where can I find these codes?

North Carolina Subscriber

Answer: What you learned was initially true, but as updates have come on line since the original ICD-10-CM publication, things have changed. While the codes still begin with an alpha character followed by a numeric character, the remaining characters may be either alpha or numeric.

For instance: You’ll find the following codes that don’t follow the original rules in “Neoplasms” chapter 2:

• C7A.0- — Malignant carcinoid tumors
• C7A.1 — Malignant poorly differentiated neuroendocrine tumors
• C7A.8 — Other malignant neuroendocrine tumors
• C7B.0- — Secondary carcinoid tumors
• C7B.1 — Secondary Merkel cell carcinoma
• C7B.8 — Other secondary neuroendocrine tumors

Similarly, you’ll find C4A.- for Merkel cell carcinoma, and new codes C49.A- for gastrointestinal stromal tumor (GIST).

As to where to find these codes, they’re still generally in numeric order. For instance, C4A lies between C43 and C44. The reason for using the “A” in the third character in this code is that C4- codes with numerals 0-9 in the third character already existed.