Coding Guidelines and Conventions
What the candidate must know
Apply the official conventions that govern code assignment. Know the meaning of includes/ excludes1/excludes2, code first/use additional code, see/see also, brackets, and the sequencing rules. Understand the principal diagnosis definition (the condition chiefly responsible for admission after study) and how it differs from the first-listed diagnosis in outpatient settings. Know the table of drugs and chemicals, neoplasm sequencing, and the general rules for combination codes and multiple coding.
Traps in questions
- Treating Excludes1 as optional - it means the two conditions are not coded together; Excludes2 means both may be coded if documented.
- Missing a code first instruction, which changes sequencing.
- Assigning a code from the alphabetic index alone without verifying in the tabular list.
- Coding a probable/inconclusive diagnosis in outpatient settings (not coded) versus inpatient (coded as if confirmed).
Rule of thumb
Always verify every code in the tabular list and obey instructional notes there; the index is a starting point, not the final answer.
Worked example: A note documents diabetes with chronic kidney disease and an Excludes1 note links the two. Because a combination code exists for diabetic CKD, assign the single combination code rather than two separate codes, and follow any code-first instruction for the CKD stage.