7th Characters and the Placeholder X in ICD-10-CM
How to add a required 7th character to an ICD-10-CM code, when to use the placeholder X, and what the injury 7th characters A, D and S mean.
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Short answer
Some ICD-10-CM categories require a 7th character, and the code is invalid without it. The 7th character must always sit in the 7th position, so when the code is shorter than six characters you fill the empty positions with the placeholder X. For injuries, A is the initial encounter (active treatment), D a subsequent encounter (healing or recovery) and S a sequela.
Key takeaways
- A code that requires a 7th character is invalid without it (Official Guidelines, Section I.A.6).
- The 7th character always goes in position 7. Fill any empty positions before it with the placeholder X.
- Some codes also use X as a placeholder inside the code (for example, many poisoning codes), and the X is required for the code to be valid (Section I.A.5).
- For injuries, 7th character A means active treatment, not the first time the patient was seen.
ICD-10-CM codes are three to seven characters long. For certain categories the 7th character is not optional: the code is invalid without it. This guide shows how to tell when a 7th character is required, how to place it correctly with the placeholder X, and how to choose the right value for injuries.
Step 1: Check whether the category requires a 7th character
The Tabular List tells you when a 7th character applies. Look for a note at the category (or above it) that lists the applicable 7th characters. The Official Guidelines (Section I.A.6) state that the applicable 7th character is required for all codes within the category, or as the notes in the Tabular List instruct.
7th characters are common in:
- Chapter 19, injury, poisoning and certain other consequences of external causes (S00–T88).
- Chapter 20, external causes of morbidity (V00–Y99), for many categories.
- Some obstetric categories in Chapter 15, where the 7th character identifies the fetus.
- Some musculoskeletal categories in Chapter 13, such as pathological fractures.
On ICD Code Finder, a code page shows "Requires 7th character" and the table of allowed values, including where the rule is defined (for example, at the category).
Step 2: Put the 7th character in position 7, using X as needed
The 7th character must always be the 7th character in the data field. If the code that needs it is not yet six characters long, fill the empty positions with the placeholder X (Section I.A.6).
Examples:
| Starting code | Characters | Valid code with 7th character A |
|---|---|---|
| S01.01 (Laceration without foreign body of scalp) | 5 | S01.01XA |
| T78.40 (Allergy, unspecified) | 5 | T78.40XA |
| T15.01 (Foreign body in cornea, right eye) | 5 | T15.01XA |
Writing "S01.01A" is a common error: the A lands in position 6, which makes the code invalid.
Step 3: Keep placeholder X characters that are part of the code
Separately from the 7th character rule, ICD-10-CM uses X as a placeholder inside some codes to allow for future expansion (Section I.A.5). Many poisoning codes work this way. For example, poisoning by 4-Aminophenol derivatives (such as acetaminophen), accidental, initial encounter, is T39.1X1A: the X fills position 5, the 1 in position 6 identifies the intent, and A is the 7th character.
Where a placeholder exists, the X must be used for the code to be considered valid.
Step 4: Choose the injury 7th character by the phase of care
For most Chapter 19 categories, the 7th character describes the encounter, not the injury (Section I.C.19.a):
- A, initial encounter: used for each encounter where the patient is receiving active treatment for the condition.
- D, subsequent encounter: used for encounters after the patient has completed active treatment and is receiving routine care during the healing or recovery phase.
- S, sequela: used for complications or conditions that arise as a direct result of a condition, such as scar formation after a burn.
Points that are often missed:
- "Initial" does not mean "first visit". A patient who is still receiving active treatment at a second visit is still A, and a patient seen for the first time by a new provider during recovery is D.
- Aftercare Z codes should not be used for aftercare of injuries; assign the acute injury code with the 7th character D instead.
- With S, code both the specific sequela and the injury code with S. The sequela is sequenced first.
Fracture categories use additional 7th characters (for example, to distinguish open from closed fractures and routine from delayed healing, nonunion or malunion). Always pick from the list printed for that category.
Step 5: Validate the finished code
Before reporting, confirm the code is complete and valid for the fiscal year of the date of service. ICD Code Finder's Code Set Builder flags codes that are missing a required 7th character, codes that are non-billable headers and codes that are not in the current code set.
Frequently asked questions
Is a code valid without its required 7th character?
No. When a category requires a 7th character, every code in it must have one. A code that has not been coded to the full number of characters required is invalid.
Why do some codes have an X in the middle?
ICD-10-CM uses X as a placeholder to keep the 7th character in the 7th position when the code has fewer than six characters, and in some categories to allow for future expansion. Where a placeholder exists, the X must be used for the code to be valid.
Does 7th character A mean the first visit?
No. For injuries, A (initial encounter) is used for each encounter where the patient is receiving active treatment for the condition. A patient seen by a new provider for the first time during the healing phase gets D (subsequent encounter), not A.
How do I code a sequela?
Use 7th character S on the injury code and also code the specific sequela (the late effect). The sequela code is sequenced first, followed by the injury code with S.
Informational, not coding advice. This page summarizes ICD-10-CM conventions for education. Always code from the medical record using the current ICD-10-CM Tabular List, Alphabetic Index and Official Guidelines for Coding and Reporting, plus payer policy.
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