Code first, use additional code, and code also

Which ICD-10-CM code should be sequenced first?

Applies to ICD-10-CM FY2027 · October 1, 2026 – September 30, 2027

The short answer

Code first appears on the manifestation and tells you the underlying cause must be sequenced before it. Use additional code appears on the underlying cause and tells you to add the manifestation after it. They are two halves of the same instruction, printed at opposite ends of the pair. Code also is different: two codes are needed but the order is yours to decide.

In ICD-10-CM FY2027, 391 codes carry a code-first note and 883 carry a use-additional note. Sequencing is not a stylistic choice in these cases — the classification has already decided it.

The etiology/manifestation convention

Official definition — Code First/Use Additional Code notes (etiology/manifestation paired codes)

Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists there is a 'use additional code' note at the etiology code, and a 'code first' note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.

In most cases the manifestation codes will have in the code title, 'in diseases classified elsewhere.' Codes with this title are a component of the etiology/ manifestation convention. The code title indicates that it is a manifestation code. 'In diseases classified elsewhere' codes are never permitted to be used as first listed or principal diagnosis codes. They must be used in conjunction with an underlying condition code and they must be listed following the underlying condition.

— ICD-10-CM Tabular List of Diseases and Injuries, FY2027, published by CDC/NCHS

The logic is that some conditions have an underlying cause and a downstream effect in a different body system. The classification wants the cause reported first so the record reads as cause-then-effect rather than a list of unrelated problems.

The give-away phrase

If a code title contains “in diseases classified elsewhere”, it is a manifestation code. Those codes are never permitted as the principal or first-listed diagnosis, and reporting one first is a sequencing error even when the code itself is correct.

Use additional code — from the other direction

A worked example

E11 (Type 2 diabetes mellitus) carries a use-additional note asking you to identify any drug used for control — insulin (Z79.4), oral antidiabetic drugs (Z79.84), or injectable non-insulin agents (Z79.85).

The diabetes code is sequenced first and the Z79 code follows. Because the note lives on E11, it applies to every code beneath it — including E11.9, where it is never reprinted.

Code also — sequencing is discretionary

Official definition — Code Also

A code also note instructs that 2 codes may be required to fully describe a condition but the sequencing of the two codes is discretionary, depending on the severity of the conditions and the reason for the encounter.

— ICD-10-CM Tabular List of Diseases and Injuries, FY2027, published by CDC/NCHS

This is the one that trips people who have learned the other two. A code-also note does not impose an order. Which code leads depends on the severity of each condition and the reason for the encounter — which means it is a judgement call informed by the documentation, not a rule you can apply mechanically.

Telling the three apart

Code first — you are on the manifestation. Something else goes before it.
Use additional code — you are on the cause. Something else goes after it.
Code also — both are needed, order depends on the encounter.

These notes are inherited

A sequencing note declared on a three-character category governs every code beneath it and is not reprinted on each one. Reading only the code you landed on is how sequencing errors happen. Every code page on this site shows inherited notes and names the ancestor that declared them — see E11.9, which inherits its use-additional note from E11.

Related: Excludes1 vs Excludes2 covers the other pair of notes that are constantly confused for each other.