MCI, Memory Loss, AMS & Delirium ICD-10

A clinician or coder at a behavioral health or SUD facility sees an older or medically complex client with cognitive symptoms — confusion, memory complaints, disorientation — and needs the right ICD-10 code now. Here is the quick answer, followed by the differential logic no single-code reference page gives you:

All four codes are billable in the FY2026 ICD-10-CM code set ( CDC NCHS ↗ ). F05 has no subcodes — it is a single code with a “code first the underlying condition” instruction.

In SUD settings the stakes are higher than a simple lookup: cognitive symptoms overlap with intoxication and withdrawal, and coding F05 when the delirium is actually substance-induced (or vice versa) creates audit exposure and medical-necessity problems at detox and residential levels of care. This guide covers each code, then the decision path connecting them — including the substance-induced differentials that single-code reference pages skip.

G31.84 — Mild Cognitive Impairment

Check your descriptor. The FY2026 official descriptor for G31.84 is “Mild cognitive impairment of uncertain or unknown etiology” — the older phrasing “mild cognitive impairment, so stated” is gone. The inclusion terms are “Mild cognitive disorder NOS” and “Mild neurocognitive disorder of uncertain or unknown etiology.” That etiology qualifier is now load-bearing: G31.84 is for cognitive decline whose cause has not been established.

The tabular’s Excludes1 list draws the boundaries precisely. G31.84 excludes, among others:

So the crosswalk to DSM-5-TR works like this, described in general terms: DSM-5-TR’s mild neurocognitive disorder — modest cognitive decline that does not interfere with independence in everyday activities — maps to G31.84 only when the etiology is uncertain or unknown. When the clinician attributes it to a known physiological condition, ICD-10-CM routes you to F06.70/F06.71 instead.

Notably for SUD facilities, G31.84 carries a “use additional code” instruction to identify contributing factors including alcohol abuse and dependence (F10.-) and tobacco use/dependence — an explicit invitation to code the substance context alongside the cognitive finding.

Documentation for G31.84: objective cognitive findings (standardized screening such as MoCA or MMSE scores, with date and administering clinician), the functional statement (decline noted but independence preserved), the absence of delirium, and the etiology statement (“etiology uncertain; medical workup in progress/unrevealing”).

• Age-related cognitive decline (R41.81) — normal aging, not a disorder
• Altered mental status (R41.82) — the nonspecific symptom code
• Mild neurocognitive disorder due to a known physiological condition (F06.7-) — when the etiology is established
• Dementia (F01.-, F02.-, F03.-) — when impairment crosses into major neurocognitive disorder
• Cognitive deficits from cerebrovascular disease (I69.-) and head injury (S06.-)

R41.3 — Other Amnesia (Memory Loss)

R41.3 is where “memory loss” lands in ICD-10-CM: the inclusion terms are Amnesia NOS and Memory loss NOS. It lives in Chapter 18 (symptoms, signs, and abnormal findings), which means it is a symptom code, not a diagnosis — and that distinction drives both when to use it and how payers treat it.

Use R41.3 when a memory complaint is real and documented but no underlying diagnosis has been established. The tabular’s Excludes1 notes route you elsewhere the moment etiology is known:

The ICD-10-CM Official Guidelines (Section I.B and the Chapter 18 guidance) say symptom codes are acceptable when no more definitive diagnosis has been established — but they are a way station, not a destination. Practically: R41.3 is defensible at intake and early in workup; carrying it as a primary diagnosis for months while billing ongoing treatment invites medical-necessity questions, and some payers are reluctant to accept symptom codes as primary on behavioral health claims at all. When the workup lands somewhere — substance-related amnestic disorder, neurocognitive disorder, dementia — the code should move with it.

• Amnestic disorder due to known physiologic condition → F04
• Amnestic syndrome due to psychoactive substance use → F10–F19 (the substance-specific amnestic codes)
• Mild memory disturbance due to known physiological condition → F06.8
• Transient global amnesia → G45.4

R41.82 — Altered Mental Status, Unspecified

“AMS” in a chart means the client’s mental status has changed in a way nobody has characterized yet — confusion, disorientation, behavioral change without an established cause. R41.82 (inclusion term: “Change in mental status NOS”) is the ICD-10-CM placeholder for exactly that: a symptom code pending workup.

Three Excludes1 notes define its edges:

That last note is the whole game: R41.82 is only correct while the cause is unknown. The moment the chart attributes the mental-status change to a UTI, hepatic encephalopathy, intoxication, or withdrawal, R41.82 is the wrong code — code the cause.

This page keeps R41.82 at the differential level deliberately; a dedicated R41.82 documentation deep-dive covers chart language, sequencing, and payer handling in depth.

• Altered level of consciousness → R40.- (somnolence, stupor, coma — when consciousness, not content, is what changed)
• Delirium NOS → R41.0 (per the tabular, unspecified delirium routes to R41.0, disorientation, unspecified)
• Altered mental status due to a known condition → code the condition — the tabular says this directly

F05 — Delirium Due to Known Physiological Condition

F05 is the acute one: a disturbance in attention and awareness, developing over hours to days, due to a documented physiological condition. The FY2026 tabular keeps F05 as a single billable code — no subcodes — with instructive inclusion terms: acute or subacute confusional state (nonalcoholic), delirium superimposed on dementia, and sundowning.

Two coding instructions matter:

• Code first the underlying physiological condition — F05 never stands alone; the infection, metabolic derangement, or other medical cause is sequenced first (the tabular gives dementia, F03.9-, as an example).
• Substance-induced delirium is excluded. The tabular carries an Excludes2 for delirium tremens, alcohol-induced or unspecified (F10.231, F10.921) — and the broader F10–F19 chapter owns every substance-induced delirium.

The SUD-facility differentiator: F05 vs. the F1x delirium codes

This is the differential that creates real audit exposure in addiction treatment, and it turns entirely on etiology:

A detox unit that codes F05 for what the chart describes as alcohol withdrawal delirium has a diagnosis that contradicts its own nursing notes — exactly the inconsistency utilization reviewers and auditors look for. The reverse error (coding F10.231 without documented withdrawal context) is just as reviewable. For the clinical picture of DTs specifically, see our delirium tremens glossary entry; for the full alcohol code family, see the F10 alcohol-related disorders guide.

The Decision Path: Which Code for Which Presentation

Run the differential in this order:

Why the wrong branch fails medical-necessity review: level-of-care criteria for detox and residential SUD treatment lean on documented withdrawal risk and active substance-related impairment. A chart that codes R41.82 for what is clinically emerging withdrawal delirium understates acuity and undermines the authorization; a chart that codes F05 for substance withdrawal misattributes it and fails consistency review. The code is not paperwork — it is the claim’s summary of your clinical reasoning.

• Known substance etiology? Intoxication or withdrawal explains the picture → F10–F19 codes (withdrawal delirium.231 pattern; intoxication delirium.x21 pattern; substance-related amnestic syndromes for memory presentations). Not F05, not R-codes.
• Known physiological condition with disturbed attention/awareness? Acute confusional state attributable to a medical cause → F05, with the underlying condition coded first.
• Isolated memory complaint, no established cause? → R41.3.
• Nonspecific confusion or mental-status change pending workup? → R41.82 — and revisit it as soon as the workup lands.
• Documented mild cognitive decline, no delirium, no dementia, etiology unknown? → G31.84. If etiology is known → F06.7-; if impairment is major → the dementia families.

Documentation Requirements by Code

Onset, course, and baseline are the three words that separate these codes in a reviewer’s eyes: acute and fluctuating points to delirium; insidious and stable points to neurocognitive decline; “always like this per family” points away from both. Build them into progress-note and assessment templates so they are captured every shift, not reconstructed at audit time. A behavioral-health EHR with structured assessments and progress notes makes that capture routine rather than heroic.

Billing & Audit Considerations

For the broader coding context, start with our ICD-10 codes glossary entry and the ICD-10 guide for addiction treatment billing.

• Symptom codes (R41.3, R41.82) as primary: acceptable under the Official Guidelines when nothing more definitive is established, but expect scrutiny when they persist across a long episode of care. Payer handling varies.
• Specificity expectations: G31.84’s etiology qualifier and the F06.7- alternative mean “MCI” alone in a chart is no longer enough — the etiology statement decides the code.
• Sequencing: F05 requires the underlying condition first; F1x deliriums carry their context in the code itself.
• Internal consistency is the audit test: diagnosis code, nursing notes, medication record, and level of care should tell one story. Claims built straight from the clinical record — the way an integrated revenue cycle workflow builds them — avoid the copy-paste drift that creates contradictions.

FAQ

What is the ICD-10 code for memory loss? R41.3 (Other amnesia — inclusion terms Amnesia NOS, Memory loss NOS), a symptom code for use when no underlying diagnosis is established. Known causes route elsewhere: F04, F06.8, the F10–F19 amnestic codes, or G45.4 for transient global amnesia.

What is the ICD-10 code for altered mental status? R41.82, Altered mental status, unspecified — a placeholder pending workup. Altered level of consciousness goes to R40.-, and AMS due to a known condition is coded to that condition.

Is G31.84 billable? Yes — G31.84, Mild cognitive impairment of uncertain or unknown etiology, is billable in FY2026. If etiology is known, use F06.7-; if the picture is dementia, use F01–F03.

Delirium vs. dementia in ICD-10? Delirium from a physiological cause is F05 (acute; code the underlying condition first; delirium superimposed on dementia is included). Dementia is chronic and codes to F01–F03. Substance-induced delirium codes to F10–F19 — never F05.

Sources: FY2026 ICD-10-CM Tabular List and code descriptions, CDC National Center for Health Statistics ↗; ICD-10-CM Official Guidelines for Coding and Reporting, FY2026 ↗ (symptom-code and Chapter 18 guidance); DSM-5-TR neurocognitive disorder framework described in original words.

Reference tables

Common questions

Official sources

• CDC NCHScdc.gov