ICD-10-CM Diagnosis Coding
Concepts to master
ICD-10-CM coding starts with the Alphabetic Index and is verified in the Tabular List. Candidates must know the official conventions: Excludes1 means the two conditions cannot be coded together, while Excludes2 means both may be coded if documented. Other conventions include includes, code first, use additional code, and code also. Specificity matters: laterality, episode of care, trimester, and seventh characters must match documentation. Combination codes capture two diagnoses or a diagnosis with a manifestation in one code. Sequela coding requires the residual condition first and the original cause as a sequela code. Z codes document factors influencing health status, and external cause codes explain injury intent and mechanism.
Traps in questions
Do not code a symptom when a definitive diagnosis is documented. In outpatient settings, do not code “probable,” “suspected,” or “rule out” diagnoses; code signs and symptoms instead. Do not infer laterality, severity, or stage. Watch acute versus chronic, and current encounter versus history. If a combination code exists, use it rather than separate codes. Verify payer-specific rules for outpatient versus inpatient uncertain diagnoses.
Worked example
A patient with type 2 diabetes and diabetic chronic kidney disease, stage 3, is seen. Assign E11.22 for diabetic chronic kidney disease and N18.30 for CKD stage 3 unspecified. Do not add a separate diabetes code. Rule of thumb: code to the highest documented specificity, and query when documentation is ambiguous rather than guessing.