In ICD-10-CM the order of your codes carries meaning. A pair of instructional notes - Code first and Use additional code - tells you which condition leads and which follows. Reversing them changes what the claim says.
Etiology and manifestation
Many conditions come in pairs: an underlying cause and the effect it produces in a particular organ or system. The classification calls these etiology and manifestation, and it has a consistent convention for them.
The underlying condition is sequenced first, and the manifestation follows. The claim then reads as a statement about cause and effect rather than two unrelated problems that happen to appear together.
Reading the two notes
| Note | Appears on | Tells you |
|---|---|---|
| Code first | The manifestation code | Something else must be sequenced before this code |
| Use additional code | The etiology code | Something else should be sequenced after this code |
They are two views of the same relationship, placed on opposite ends of it. Encountering either one tells you a second code is expected and tells you which position each occupies.
Code also is different
A third note, Code also, is often confused with these two. It indicates that two codes may be needed to fully describe the condition, but it does not dictate sequencing. The order is determined by the circumstances of the encounter - usually by which condition was chiefly responsible for the visit.
So: Code first and Use additional code fix the order. Code also does not.
Manifestation codes cannot stand alone
Certain manifestation codes are never permitted as a principal or first-listed diagnosis. Where the classification enforces this, the code exists only as the second half of a pair, and submitting it alone produces an invalid claim.
These codes are identifiable by their Code first note, which names the underlying conditions expected to precede them. If you find yourself with such a code and no candidate for the first position, that is a signal to go back to the record - the underlying condition is either documented somewhere you have not looked, or it needs to be queried.
Why sequencing has consequences
For outpatient claims, the first-listed diagnosis establishes the reason for the encounter and drives medical-necessity decisions. For inpatient stays, the principal diagnosis is a primary input into which MS-DRG the stay groups to, and therefore into what the stay pays. Sequencing is not a cosmetic detail.
See how MS-DRGs work for what the principal diagnosis actually drives.
Where to find the notes
Instructional notes are attached at several levels of the classification. A note at chapter, section or category level applies to every code beneath it, so the note governing your code may not be printed on the code itself.
Every ICD-10-CM code page on this site displays the Code first, Use additional code and Code also notes that apply, each clearly labelled, alongside the includes and excludes notes. Reading them before you sequence is faster than correcting a rejected claim afterwards.