Medical Coding (ICD-10-CM)

What ICD-10-CM is

ICD-10 is the World Health Organization's International Classification of Diseases, 10th revision. ICD-10-CM is the clinical modification used in the United States for coding diagnoses. ^[1,2] Codes turn clinical findings into a standard form that can be counted, compared, and billed.

Good coding supports accurate health records, public-health statistics, research, and reimbursement.

How a code is built

• Codes are 3 to 7 characters long. ^[2]
• The first character is always a letter; the second is a number.
• The first three characters form the category (for example E11 — type 2 diabetes mellitus).
• Characters after the decimal point add detail such as cause, body site, severity, or complications.
• A 7th character, where required, adds information such as the episode of care (initial, subsequent, or sequela) for injuries. ^[2]

Chapters you will meet often

• E00–E89 — endocrine, nutritional, and metabolic diseases.
• I00–I99 — diseases of the circulatory system.
• J00–J99 — diseases of the respiratory system.
• K00–K95 — diseases of the digestive system.
• S00–T88 — injury, poisoning, and other consequences of external causes. ^[3]

Core coding principles

Code to the highest level of specificity the documentation supports, and only from what a clinician has documented. If the note is unclear, the coder queries the clinician rather than guessing. ^[2]

Pay attention to instructional notes in the code book, such as 'Excludes1' (the two conditions cannot be coded together) and 'code also' instructions. ^[2]

Common primary-care examples

• I10 — essential (primary) hypertension.
• E11.9 — type 2 diabetes mellitus without complications.
• E78.5 — hyperlipidaemia, unspecified.
• J45.909 — unspecified asthma, uncomplicated.
• J44.9 — chronic obstructive pulmonary disease, unspecified. ^[3]