Purpose of ICD-10-CM
A standardized coding system used in the U.S. to classify diagnoses, symptoms, and procedures.

Supports clinical documentation, billing, epidemiological tracking, and quality improvement.

🧩 Key Concepts
1. Structure of ICD-10-CM Codes
Each code has 3–7 characters.

First character: Always a letter.

Characters 2–3: Numeric, define the category.

Characters 4–7: Alphanumeric, provide clinical detail (e.g., severity, location, laterality).

Example:

M54.5 – Low back pain

E11.9 – Type 2 diabetes mellitus without complications

S52.521A – Displaced fracture of left radius, initial encounter

2. Categories of Codes
A00–B99: Infectious diseases

C00–D49: Neoplasms

E00–E89: Endocrine, nutritional, and metabolic diseases

F01–F99: Mental and behavioral disorders

I00–I99: Circulatory system

J00–J99: Respiratory system

K00–K95: Digestive system

M00–M99: Musculoskeletal system

Z00–Z99: Factors influencing health status (e.g., routine exams, social determinants)

3. Laterality
Codes often specify right, left, or bilateral involvement.

Example:

H52.03 – Hypermetropia, bilateral

S93.401A – Sprain of unspecified ligament of right ankle, initial encounter

4. Placeholder “X”
Used when a code requires a 7th character but lacks preceding characters.

Example: T15.91XA – Foreign body in eye, initial encounter

5. 7th Character Extensions
A – Initial encounter

D – Subsequent encounter

S – Sequela (complication or condition resulting from a previous disease)

6. Z Codes
Used for non-disease conditions: screenings, history, social factors.

Examples:

Z00.00 – General adult medical exam

Z63.5 – Disruption of family by separation or divorce

Z59.0 – Homelessness

7. Coding Guidelines
Always code to the highest level of specificity.

Use combination codes when applicable (e.g., diabetes with complications).

Avoid unspecified codes unless documentation is incomplete.

📝 Practice Quiz (15 Questions + Answers)
1. What does ICD-10-CM stand for? Answer: International Classification of Diseases, 10th Revision, Clinical Modification

2. How many characters can an ICD-10-CM code have? Answer: 3 to 7 characters

3. What does the first character of an ICD-10-CM code represent? Answer: A letter indicating the chapter/category

4. What does the code M54.5 represent? Answer: Low back pain

5. Which code category covers mental and behavioral disorders? Answer: F01–F99

6. What does the 7th character “A” indicate? Answer: Initial encounter

7. What is the purpose of the placeholder “X”? Answer: To maintain code structure when a 7th character is required

8. What does Z00.00 represent? Answer: General adult medical examination

9. Which code would be used for homelessness? Answer: Z59.0

10. What does E11.9 represent? Answer: Type 2 diabetes mellitus without complications

11. What is the significance of laterality in ICD-10-CM codes? Answer: It specifies whether the condition affects the right, left, or both sides

12. What does the 7th character “S” indicate? Answer: Sequela (a condition resulting from a previous illness)

13. Which chapter includes codes for the respiratory system? Answer: J00–J99

14. What is the best practice when selecting an ICD-10-CM code? Answer: Code to the highest level of specificity

15. What type of conditions are Z codes used for? Answer: Non-disease conditions like screenings, social factors, and history