Manifestation Codes: What Goes First, and Why It Can’t Be the Manifestation

Three authorities say the same thing here, which is unusual — and worth keeping apart anyway, because each covers a slightly different set of codes.

1. The Official Guidelines, Section I.A.13 (etiology/manifestation convention)

Official source

“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, if applicable, 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.”

On the codes whose titles carry the phrase, the Guidelines are absolute:

Official source

“‘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.”

The same section names category F02 as its worked example of the convention, and points to the Alphabetic Index structure: both conditions appear together, etiology first, manifestation in brackets — the code in brackets is always sequenced second.

2. The Tabular List’s paired notes

The convention is visible in the book as two halves of one instruction. The etiology code carries Use Additional Code; the manifestation code carries Code First. They are written to be read together, and when you can see both, the sequencing question is already answered.

3. The Medicare Code Editor (v44.0, edit 06)

MCE edit 06 — “manifestation codes not allowed as principal diagnosis” — lists 422 codes that a Medicare inpatient claim cannot lead with. This is a payer edit, not a classification rule, and its list is not identical to the set of codes whose titles say “in diseases classified elsewhere”: it is broader (see the folk-rule section below). Note also that the guidelines cover first-listed and principal, so the convention governs outpatient claims the MCE never touches.

The Guidelines’ own example, walked through both halves. A patient with Parkinson’s disease has documented moderate dementia without behavioral disturbance.

The etiology side.Category G20 (Parkinson’s disease) carries a Use Additional Code note naming exactly which dementia codes may follow it:

Official source

Use additional code, if applicable, to identify: dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4); dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-); dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3); dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2); dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0); mild neurocognitive disorder due to known physiological condition (F06.7-)

The manifestation side. Category F02 carries the matching Code First note, listing the underlying conditions its dementia codes may follow — Alzheimer’s (G30.-), Parkinson’s disease (G20.-), traumatic brain injury (S06.-), Huntington’s disease (G10), HIV disease (B20), and roughly twenty more.

The claim writes itself, in this order:

1. G20.- — Parkinson’s disease (principal / first-listed)
2. F02.B0 — Dementia in other diseases classified elsewhere, moderate, without behavioral disturbance (secondary)

Reverse them and three things go wrong at once: the Guidelines’ sequencing rule is broken, the MCE rejects the claim (every billable F02 code is on the edit-06 list), and the record no longer says what caused the dementia. Note too that the severity in the documentation is what selects F02.B0 over F02.80 — and in the V28 risk model that choice moves the patient from HCC 127 to HCC 126.

If the manifestation code’s title does not say “in diseases classified elsewhere.” The convention still applies. The Guidelines say so directly: “There are manifestation codes that do not have ‘in diseases classified elsewhere’ in the title. For such codes, there is a ‘use additional code’ note at the etiology code and a ‘code first’ note at the manifestation code, and the rules for sequencing apply.” D63.1 (Anemia in chronic kidney disease) is the clean example — no such phrase in the title, a Code First note for the underlying CKD (N18.-), and a place on the MCE edit-06 list all the same.

If the Code First note is not part of an etiology/manifestation pair. Some Code First and Use Additional Code notes are pure sequencing instructions on codes that are not manifestations at all — the Guidelines close I.A.13 by saying so. Read what the note actually names rather than assuming the code is a manifestation because it carries a Code First.

If the Code First note says “such as.” The list is illustrative, not exhaustive. N08 (Glomerular disorders in diseases classified elsewhere) names amyloidosis, gout, multiple myeloma, sepsis, sickle-cell disease and others under “code first underlying disease, such as:” — a documented underlying disease outside that list still sequences first. What the list is useful for: its companion Excludes1 entries name the combinations that have their own dedicated codes instead.

If a dedicated combination code exists. Check the manifestation code’s Excludes1 before pairing anything. N08’s Excludes1 sends diabetic nephropathy to E08-E13 with .21, lupus nephritis to M32.14, and gonococcal glomerulonephritis to A54.21 — single codes that replace the two-code pair entirely.

If the etiology is not documented. There is no fallback code, and the manifestation cannot stand alone in first position. This is a provider query: what underlying condition is the manifestation attributed to? Coding the manifestation alone leaves a claim that the classification, and often the editor, will not accept.

Two tests, applied in this order, settle nearly every case without looking anything up beyond the code’s own page:

1. Does the title say “in diseases classified elsewhere”? If yes, it is a manifestation code by construction — 163 billable codes carry that phrase — and it is never first-listed or principal. The largest families are osteopathy (M90.-), myositis (M63.-), spondylopathies (M49.-), and the ear, eye and nervous-system “in diseases classified elsewhere” categories.
2. Does it carry a Code First note? If yes, something sequences ahead of it, whether or not the title advertises it. This is the test that catches D63.1 and its kind.

The mirror-image test works from the other side: a code carrying Use Additional Code is an etiology, and the note names the manifestations it expects to be followed by. When you can see both notes — one on each code — you are looking at a matched pair, and the sequencing is not a judgment call.

The folk rule: “if the title says ‘in diseases classified elsewhere,’ it can’t be principal — so if it doesn’t say that, it can.” The first half is exactly right and comes straight from the Guidelines. The second half is an inference nobody wrote down, and it is false.

What is actually true: the title phrase is a sufficient marker of a manifestation code, not a necessary one. The MCE’s manifestation list runs to 422 codes while only 163 billable codes carry the phrase, and the gap is populated by codes like D63.1 (Anemia in chronic kidney disease) — plainly a manifestation, plainly Code-First-bound, and plainly missing the tell. The reliable test is the note, not the title.

The shortcut survives as long as you only ever meet titled manifestation codes, which is why it holds up for most coders most of the time. It fails on exactly the codes that are easiest to sequence wrong, because nothing in the title warns you.

1. Recognize the manifestation code: “in diseases classified elsewhere” in the title, or a Code First note, or a bracketed code in the Index.
2. Code the underlying etiology first — the Index lists it first, with the manifestation in brackets.
3. Sequence the manifestation code second; it is never principal or first-listed.
4. Read the etiology code’s Use Additional Code note for the specific manifestation code to add.
5. For Medicare inpatient claims, MCE edit 06 rejects the manifestation code as principal — a consequence of the rule, not a second rule.

• The manifestation code as principal because it was the reason for the visit.
• The manifestation code without the etiology code.
• Reversing the order of the pair.

• The underlying condition — required for the manifestation code to be reported at all.
• The specific manifestation (e.g., dementia with or without behavioral disturbance) selecting the code.