ICD-10-CM has been the standard diagnostic code set for some time—ICD-10 was implemented in 2015, after all—but the tenth revision is still complex enough to occasionally cause headaches for the healthcare community. But don’t worry. The ICD-10 headaches have stopped today – at least as far as the ICD-10 code structure is concerned – because the codes are segmented in a standardized way, which means they can be broken down into smaller (and less intimidating) small pieces. So, let’s dig into the ICD-10 encoding structure and understand it one by one.

First six characters of the ICD-10 code structure

Codes in the ICD-10-CM code set can contain three to seven characters. The more characters, the more specific the diagnosis. The first character is always a letter (that is, a letter), but the second through seventh characters can be letters or numbers. Let’s look at an example.

category

The first three characters of the ICD-10 code structure designate the category of diagnosis. In this case, the letter “S” indicates that the diagnosis concerns “injury, intoxication and certain other consequences of extrinsic origin associated with a single body region”.

The “S” is used in conjunction with the numerals “8” and “6” to indicate that the diagnosis is in the category of “calf muscle, fascia, and tendon injuries.” Three-character categories with no further subdivision (i.e., no greater specificity) can be coded on their own. In this case, however, there can be greater specificity, and you should fill in as many “blanks” as possible.

Etiology

The next three characters (characters three through six) indicate the relevant etiology (ie, cause, set of causes, or mode of cause and effect of a disease or condition), anatomical site, severity, or other important clinical details. So, in this case, the numbers “0”, “1” and “1” represent a diagnosis of “right Achilles tendon strain”.

tricky seventh character

Finally, there is a seventh character: the extension.According to CMS, it “provides[s] Information about the characteristics of the encounter. ” However, you can only assign the seventh character to specific codes in certain ICD-10-CM categories. To determine which categories qualify for the seventh character, you must refer to the code table list – It can be found in Chapter 19 (Injury, Poisoning, and Certain Other Consequences of External Causes), Chapter 15 (Pregnancy, Childbirth and the Puerperium), and sometimes Chapter 13 (Musculoskeletal System and Connective Tissue Disorders).

Extended characters must always be in the seventh position. Therefore, if the code is less than six characters and a seventh character expansion is required, all empty character spaces must be filled with the placeholder “X”.

Seventh character expansions with injuries (excluding fractures) include:

A – first encounter. This describes the entire period during which a patient is actively treated as a result of injury, poisoning, or other extrinsic consequences. So you can’t just use “A” as the seventh character in the first statement. In fact, you can use it for a variety of claims.

D – Subsequent encounters. This describes any encounter following the active phase of therapy, when the patient receives usual care for the injury while healing or recovering. (This often includes rehabilitation.) In the example above, we assumed that the doctor referred the patient to a physical therapist to rehabilitate the patient’s sprained Achilles tendon. Rehabilitation would be considered part of the healing and recovery phase, so you could code “subsequent encounters”, thus assigning the seventh character “D”.

S – sequelae. The seventh character expansion “S” indicates a complication or condition as a direct result of the injury. An example of after effects are scars from burns.

Multiple codes, single condition

In some cases, you may need to record multiple codes for a single condition. A note in the table listing indicates if you need to report more than one code. These annotations use wording such as “use additional code” or “code first”. (“Code first” means that you should code the base condition first.) Remember that ICD-10 also includes combination codes, which are used to classify two or more conditions that often occur together single code.

For injury codes, you will typically submit an external cause code to further describe the circumstances that led to the injury. You can find these codes in Chapter 20: External Reason Codes. These are secondary codes, meaning they further describe the cause of the injury or health condition by capturing how the event happened (cause), the intent (intentional or accidental), where the event occurred, and the activities the patient performed at the scene. The time of the incident and the identity of the person (for example, civilian or military). You can assign as many external reason codes as you need to explain the patient’s condition as fully as possible.

In this case, imagine a patient strains his Achilles tendon while running on a treadmill at the gym. To code for this specific set of conditions, you’ll need activity codes, location codes, and external cause status codes.

As shown above, the appropriate activity code for running on a treadmill is Y93.A1; the place code for the gym where it occurs is Y92.39; in this case the external reason status code would be Y99.8, i.e. not for Recreation or sports during student time.

So, in this example, you’d submit a total of four ICD-10 codes to accurately describe a patient with a right Achilles tendon sprain, an injury sustained while the patient was running recreationally on a treadmill at the gym.

important notes

Knowing the ICD-10 code structure will help simplify your coding process, but there are some random bits of information that rehabilitation therapists should know:

• In addition to the norms in Chapter 19: Injuries, Poisoning, and Certain Other Extrinsic Consequences, many norms applicable to rehabilitation therapists appear in Chapter 13: Disorders of the Musculoskeletal System and Connective Tissue. Most of these codes have site and lateral designations to describe the bone, joint, or muscle associated with the patient’s condition.
• For conditions that involve more than one site, such as osteoarthritis, there is often a “multiple site” code. If no “multiple site” codes are available, you should report multiple codes to indicate all the different sites involved.
• In some treatment options, the lower end of the bone is affected (eg osteoporosis, M80, M81). Although the affected area may be in a joint, the affected area is still considered a bone, not a joint.
• Many musculoskeletal disorders are the result of previous injury or trauma, or are recurrent disorders. Most bone, joint, or muscle conditions that result from a healed injury appear in Chapter 13 (Chapter “M”). This chapter also covers most recurrent bone, joint, or muscle disorders. Therefore, while you should generally code chronic or recurrent injuries using Chapter 13 codes, you should code current acute injuries using the appropriate injury codes from Chapter 19.
• Some codes in Chapter 13 (Musculoskeletal System and Connective Tissue Disorders) may require external cause codes in addition to the musculoskeletal condition codes to help identify the underlying cause of the condition.

look? The ICD-10 code structure isn’t that scary when broken down and examined one by one. You can appreciate how the specificity provided in this structure facilitates the medical coding of diseases and injuries in all specialties. That said, if you still have questions, we understand. Feel free to drop them below and we’ll do our best to help you.