On October 1, 2015, the ICD-9-CM (International Classification of Diseases, Ninth Revision, Clinical Modification) code sets used by healthcare providers in the U.S. to report medical diagnoses and inpatient procedures was replaced by ICD-10-CM (International Classification of Diseases, 10th Revision, Clinical Modification) code sets.

The U.S., which implemented the ICD-9 code sets in 1979, was slow to make this transition. Most industrialized countries moved to ICD-10 several years ago. In fact, some countries are already preparing for ICD-11, which is expected to be released in 2018.

But healthcare providers in the U.S. should not start planning for the ICD-11 year. They can expect to use ICD-10 for many years. This is why it is critical to understand the difference between ICD-9-CM diagnosis codes, which U.S. providers used for more than 35 years, and ICD-10 diagnosis codes.

Here are 10 differences to know

1. Number of codes. ICD-9-CM had approximately 14,000 codes. ICD-10-CM, at the time of the transition, had about 69,000 codes for providers to choose from. The increase in number of codes is intended to help providers better capture specificity.

2. Appearance. ICD-9-CM codes had 3-5 digits. The first digit is alpha (E or V) or numeric. Digits 2-5 are numeric. A decimal is placed after the third character.

ICD-10-CM codes have seven digits. Digit 1 is alpha. Digit 2 is numeric. Digits 3–7 are alpha or numeric. A decimal is still placed after the third character.

As an example, let’s look at a femur fracture. There were 16 ICD-9-CM codes associated with a femur fracture, including 821.11 (open fracture of shaft of femur). There are 1,530 ICD-10-CM codes associated with a femur fracture, including S72.352C (displaced comminuted fracture of shaft of left femur, initial encounter for open fracture type IIIA, IIIB, or IIIC).

3. Laterality. With ICD-10-CM, providers can identify laterality — whether a treatment was performed on a part of the body on the left or right side. This was lacking in ICD-9-CM.

The addition of laterality was a major contributor to the expansion in the number of codes, with right or left options accounting for more than 40% of ICD-10-CM codes.

4. Specificity. The addition of laterality isn’t the only new way to more specifically identify health conditions. Providers can now identify etiology, anatomical site and severity.

5. Expandability. New procedures are frequently developed, and new illnesses are frequently identified. ICD-9-CM had essentially no ability to expand to include such necessary additions.

But ICD-10-CM is ready for expansion. Its use of a placeholder of “X” with certain ICD-10-CM codes allows for expansion and/or to fill out empty characters when a code contains fewer than six characters and a seventh character applies.

6. Definitions. Some ICD-10-CM codes redefine definitions used in ICD-9-CM. For example, in ICD-9-CM, a subsequent episode of care for acute myocardial infarction was considered within eight weeks while in ICD-10-CM, it is considered within 4 weeks.

7. Injury identification. In ICD-9-CM, injuries were grouped by type. In ICD-10-CM, injuries are group by anatomical site.

8. E and V codes. In ICD-9-CM, the codes corresponding to V codes (factors influencing health status and contact with health services) and E codes (external causes of injury and poisoning) were separated into supplementary classifications. In ICD-10, they are incorporated into the main classification.

9. “Excludes” notes. ICD-9-CM included a single type of excludes note, but its definition was vague. This placed the burden on the coder to determine which meaning applied. It could have meant that a coder should not use a particular code for a particular condition or that a condition was not included in a particular code. In the first scenario, a coder needed to check other categories for the correct code. In the second scenario, a coder needed to assign both codes when patients had both conditions simultaneously (if applicable).

ICD-10-CM includes two excludes notes, and defines them.

“Excludes 1” indicates that the code excluded should never be used with the code where the note is located (do not report both codes) An example is Q03 – Congenital hydrocephalus; excludes 1: Acquired hydrocephalus (G91.-).

“Excludes 2” indicates that the condition excluded is not part of the condition represented by the code but a patient may have both conditions at the same time, in which case both codes may be assigned together (both codes can be reported to capture both conditions). An example is L27.2 – Dermatitis due to ingested food; excludes 2: Dermatitis due to food in contact with skin (L23.6, L24.6, L25.4).

10. New concepts. There are new concepts included in ICD-10-CM that did not exist in ICD-9-CM. These include blood type, the Glasgow Coma Scale and alcohol level.