Code First, Use Additional Code, and Code Also: What Each Note Requires, and Which Ones Set the Order

The tabular uses three instructional notes that all say “you may need another code.” Two of them also say which code goes first; one does not. That is the whole distinction, and the FY 2027 tabular carries roughly 360 Code First blocks, 850 Use Additional Code blocks and 330 Code Also blocks, so it comes up on most pages.

The two notes were designed as a pair. Section I.A.13 introduces them for the etiology/manifestation convention:

Official source

“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.”

So the same rule is written twice, once at each code. D63.1, Anemia in chronic kidney disease, carries “Code First underlying chronic kidney disease (CKD) (N18.-)”; category N18 is the code that leads. The manifestation guide linked below walks the full convention, including the “in diseases classified elsewhere” codes that can never be principal.

The same section then says the pair is not limited to that convention:

Official source

“‘Code first’ and ‘Use additional code’ notes are also used as sequencing rules in the classification for certain codes that are not part of an etiology/ manifestation combination.”

Section I.B.7 spells out what each note means outside the convention:

Official source

“‘Use additional code’ notes are found in the Tabular List at codes that are not part of an etiology/manifestation pair where a secondary code is useful to fully describe a condition. The sequencing rule is the same as the etiology/manifestation pair, ‘use additional code’ indicates that a secondary code should be added, if known.”

Official source

“‘Code first’ notes are also under certain codes that are not specifically manifestation codes but may be due to an underlying cause. When there is a ‘code first’ note and an underlying condition is present, the underlying condition should be sequenced first, if known.”

Two phrases matter: if known, and, for Use Additional Code, useful to fully describe. A Use Additional Code note is not a demand for a code that the record does not support — J45, Asthma, asks for tobacco exposure or dependence codes only when they apply. And the Guidelines’ own I.B.7 example is the organism: a bacterial infection outside chapter 1 carries a Use Additional Code note for B95 or B96 “to identify the bacterial organism causing the infection.”

A Use Additional Code note can ask for more than one code

I13.0 carries two: “Use additional code to identify type of heart failure (I50.-)” and “Use additional code to identify stage of chronic kidney disease (N18.1-N18.4, N18.9).” I13.0 leads, and both secondary codes follow. Category I50 carries the mirror-image Code First for heart failure due to hypertension with CKD (I13.-).

The “if applicable” variant

Official source

“‘Code, if applicable, any causal condition first’ notes indicate that this code may be assigned as a principal diagnosis when the causal condition is unknown or not applicable. If a causal condition is known, then the code for that condition should be sequenced as the principal or first-listed diagnosis.”

This is the softer Code First. Where a plain Code First note marks a code that goes second whenever its cause is present, the “if applicable” form leaves the code free to lead when there is no cause to name.

Official source

“A ‘code also’ note instructs that two codes may be required to fully describe a condition, but this note does not provide sequencing direction. The sequencing depends on the circumstances of the encounter.”

That is the entire definition, and it is exactly what Code Also lacks compared with the pair above. The tabular writes the note at both members when the relationship is symmetrical: I34.0, Nonrheumatic mitral insufficiency, carries “Code also, if applicable: nonrheumatic mitral (valve) annulus calcification (I34.81),” and I34.81 carries “Code also, if applicable: nonrheumatic mitral (valve) insufficiency (I34.0) / nonrheumatic mitral (valve) stenosis (I34.2).” Neither is the underlying cause of the other, so neither note can say which goes first — the one chiefly responsible for the encounter leads, by the ordinary principal / first-listed test.

Category J44 shows the note pointing one way: “Code also type of asthma, if applicable (J45.-).” A COPD patient with a documented asthma type gets both codes; which leads depends on what the encounter was for.

The trap is reading Code Also as if it were Code First. Claim Check reports Code Also relationships as a separate class from the sequencing notes precisely because the correct response is different: for Code First or Use Additional Code, the tool is checking an order; for Code Also, it is checking only that the second code was considered.

1. Anemia documented as due to stage 3a chronic kidney disease. D63.1 carries Code First for N18.-: N18.31 first, D63.1 second. The order is fixed by the note.
2. Hypertensive heart and kidney disease with chronic systolic heart failure and stage 4 CKD. I13.0 carries two Use Additional Code notes: I13.0 first, then I50.22 and N18.4. The combination code leads; both secondaries follow it.
3. Nonrheumatic mitral insufficiency with annulus calcification. I34.0 and I34.81 carry reciprocal Code Also notes: both I34.0 and I34.81 are reported, in whichever order the encounter’s circumstances dictate. Neither note decides.

1. Read every instructional note at the code in hand, in the Tabular.
2. Code First: sequence the named underlying condition before this code when it is documented; an “in diseases classified elsewhere” code can never lead.
3. Use Additional Code: this code leads; add the secondary code after it if the record supports it (“if known”).
4. Code Also: report the second code when the condition is documented; sequence by the circumstances of the encounter.
5. “Code, if applicable, any causal condition first”: this code may lead when no causal condition is known.

• Treating Code Also as if it fixed the order.
• Adding the Use Additional code without documentation of the secondary condition.
• Sequencing a Code First code ahead of its documented underlying condition.
• Assuming Code First appears only on manifestation codes — I50 and D63 are examples where it appears elsewhere.

• Whether the underlying condition a Code First note names is documented.
• Whether the secondary condition a Use Additional Code note names is documented.
• Which condition was the reason for the encounter — the only sequencing key a Code Also pair has.