Category · F30-F39 block
F31 — Bipolar affective disorder
Terminology note: "Bipolar" here refers specifically to a documented course of at least two episodes of disturbed mood and activity, at least one of which must be manic, hypomanic, or mixed — a course requirement, not a description of mood swings in ordinary conversational usage. A person with only ever depressive episodes, however many, is not bipolar under this definition; see F33.
What is this category?
F31's core requirement is course, not symptom severity: the person must have had at least one manic, hypomanic, or mixed episode at some point, documented either now or in the past. Once that course is established, the fourth character records the type and severity of the current (or most recent) episode — hypomanic, manic (with or without psychotic symptoms), depressive (at three severity levels, with or without psychotic symptoms), mixed, or in remission.
Core diagnostic concept
Two separate judgments are needed for F31: first, has an elevated-pole (manic, hypomanic, or mixed) episode ever been documented for this person, at any point, which is what actually makes the course bipolar; second, what is the type and severity of the current episode, which determines the fourth character. Skipping the first judgment and classifying purely from whatever episode is currently in front of you is the single most common error with this category.
Key diagnostic features
- A documented course of at least two mood episodes
- The current episode plus at least one other, with at least one of the episodes in the course being manic, hypomanic, or mixed.
- Current episode type and severity
- Hypomanic, manic (with/without psychotic symptoms), depressive (mild/moderate/severe, with/without psychotic symptoms), or mixed, recorded as the fourth character.
- Mixed features
- Manic and depressive symptoms occurring together or alternating rapidly within the same episode, rather than one pole cleanly followed by the other.
- Remission
- A distinct fourth-character option (F31.7) for a person with a documented bipolar course who currently has no significant mood disturbance, rather than treating remission as 'no diagnosis'.
How to weigh evidence
These learning labels are teaching aids, not official ICD-10 terminology (see Sources and Method).
- supports A person now presenting with a severe depressive episode who has a clearly documented manic episode from several years earlier.
- consistent not decisive A person describes feeling 'a bit up and down' generally, without a clinically significant manic, hypomanic, or mixed episode ever having been identified.
- raises alternative Two or more depressive episodes with no elevated-pole episode ever documented, however severe or recurrent — this points toward F33, not F31.
- contradicts or weakens A single manic episode with no prior or subsequent episode of any kind yet documented — this weighs toward F30, not F31, until a second episode occurs.
- missing and necessary to ask Whether an elevated-pole episode has ever occurred, at any point in this person's history, even if the current presentation is purely depressive.
Diagnostic boundary
F31 requires a documented course of at least two episodes with at least one being manic, hypomanic, or mixed; the current episode's type and severity then sets the fourth character. A single manic episode alone is F30, and any number of depressive-only episodes is F33, not F31.
Full comparisons:
Duration and course
Minimum duration: Each episode within the course follows the same duration conventions as its own episode type (roughly one week for mania/hypomania, two weeks for a depressive episode).
Course: Episodes are typically separated by periods of substantially or completely normal mood and functioning; the interval between episodes varies widely between individuals.
Included presentations
- A current depressive episode in a person with a documented prior manic or hypomanic episode.
- A current manic episode in a person with a documented prior depressive episode.
- A current mixed episode, with manic and depressive features occurring together or alternating rapidly.
- A person with a documented bipolar course who is currently in remission.
Exclusions and distinguishing presentations
| If this is true instead… | Consider | Why |
|---|---|---|
| A single manic episode with no other episode of any kind ever documented | F30 | A single elevated-pole episode without a second episode of either pole does not yet meet bipolar's course requirement. |
| Recurrent depressive episodes with no elevated-pole episode ever documented | F33 | Recurrence of depression alone, without a manic, hypomanic, or mixed episode, is classified as recurrent depressive disorder, not bipolar affective disorder. |
| Persistent, subthreshold mood instability that has never reached full-episode severity in either direction | F34 | Chronic subthreshold mood swings are classified under the persistent mood disorders, not bipolar affective disorder, unless a full-threshold episode has actually occurred. |
Four-character subtypes (orientation)
A learner should never assign an F31 fourth character purely from the current episode without first confirming the course requirement (a documented elevated-pole episode at some point). Subtypes marked orientation-only here are taught in principle but not separately assessed in this pilot.
- F31.0 — Bipolar affective disorder, current episode hypomanic
- Documented bipolar course, current episode mildly elevated without significant impairment. (in_depth)
- F31.1 — Current episode manic, without psychotic symptoms
- Documented bipolar course, current episode manic without delusions or hallucinations. (in_depth)
- F31.2 — Current episode manic, with psychotic symptoms
- Documented bipolar course, current manic episode with delusions or hallucinations. (taught for orientation only, not separately assessed in this pilot)
- F31.3 — Current episode mild or moderate depression
- Documented bipolar course, current depressive episode of mild or moderate severity. (in_depth)
- F31.4 — Current episode severe depression without psychotic symptoms
- Documented bipolar course, current depressive episode severe, without psychotic features. (in_depth)
- F31.5 — Current episode severe depression with psychotic symptoms
- Documented bipolar course, current severe depressive episode with delusions or hallucinations. (taught for orientation only, not separately assessed in this pilot)
- F31.6 — Current episode mixed
- Manic and depressive symptoms occurring together or alternating rapidly within the same episode. (in_depth)
- F31.7 — Currently in remission
- Documented bipolar course, no significant current mood disturbance. (in_depth)
- F31.8 — Other bipolar affective disorders
- A bipolar presentation not matching the other listed subtypes. (taught for orientation only, not separately assessed in this pilot)
- F31.9 — Bipolar affective disorder, unspecified
- A bipolar course identified but without enough information to specify the current episode further. (taught for orientation only, not separately assessed in this pilot)
External causes to check first
Categories in this block require that the disturbance is not better explained by another external cause listed below. These short capsules are reminders, not full teaching modules.
External cause capsule — Affective disorders with psychotic features
A reminder to check whether psychotic symptoms are confined to, and explained by, a manic or depressive episode, before applying F20 or F25.
What to check:
- Whether psychotic symptoms (e.g. mood-congruent delusions of guilt or grandiosity) appear only during a clearly established manic or depressive episode and resolve as the mood episode resolves.
- Whether mood symptoms clearly preceded the psychotic features, or vice versa.
- Whether the delusional content is mood-congruent (fitting the prevailing mood, e.g. grandiose ideas during mania) rather than the more mood-neutral or bizarre content typical of F20.
- Whether this pattern has recurred across more than one episode, which would raise consideration of F25 rather than a simple mood disorder with psychotic features.
The full F30-F39 category pages (F30, F31, F32, F33) themselves, which cover the severity-and-psychotic-features gradient for manic and depressive episodes in depth; this capsule is a focused reminder of the boundary against F20/F25, not a substitute for those pages.
External cause capsule — Organic, medical, or substance-related mood presentations
A reminder that a manic or depressive presentation can be caused by a general medical condition (e.g. thyroid disease, stroke) or by a substance or medication (e.g. corticosteroids, stimulant intoxication, sedative/alcohol withdrawal) rather than being a primary F30-F39 mood disorder, and that this should be actively considered before a primary mood-disorder classification is settled.
What to check:
- Timing: did the mood symptoms begin during or shortly after starting, stopping, intoxication with, or withdrawal from a substance or medication known to affect mood?
- Medical context: is there a known medical condition (e.g. thyroid disease, corticosteroid treatment, a neurological condition) with a recognised association with mood disturbance?
- Course after the cause is addressed: a mood presentation that substantially improves once the medical condition is treated or the substance/medication is stopped weighs toward a secondary cause rather than a primary mood disorder.
- Whether mood symptoms clearly predated the medical condition, substance use, or medication in question, which would argue against a purely secondary explanation.
A full teaching module on F10-F19 (substance-related disorders) or a general medical work-up, both of which are outside this capsule's scope.
Worked example — checking course history before classifying a current depressive presentation
A 41-year-old woman presents with two weeks of low mood, loss of interest in activities she usually enjoys, poor sleep, and reduced appetite, meeting the threshold for a severe depressive episode without psychotic features. Her chart notes that four years ago she had a two-week period of markedly elevated mood, decreased need for sleep, and grandiosity that required brief hospitalisation, from which she fully recovered.
- Step 1 — Assess the current episode on its own terms: two weeks of low mood, anhedonia, poor sleep, and reduced appetite meet criteria for a severe depressive episode.
- Step 2 — Check psychotic features for the current episode: none described, so 'without psychotic symptoms.'
- Step 3 — Check the decisive course question: the chart documents a prior manic episode four years ago that required hospitalisation.
- Step 4 — Apply the course requirement: because an elevated-pole episode has been documented at any point in this person's history, the course is bipolar, not a single depressive episode.
- Conclusion — F31.4, Bipolar affective disorder, current episode severe depression without psychotic symptoms — not F32 (a single depressive episode), because the prior manic episode establishes the bipolar course.
Interactive practice
- Type A A manic episode, with a depressive one on record Recognition / application · Foundation
- Type B "One manic episode is enough to call it bipolar" Boundary discrimination · Foundation
- Type C A rumour of a wild phase, years ago Insufficient information · Developing
Retrieval prompts
Try answering each of these from memory before revealing where to check. Nothing you think or type here is sent or saved anywhere.
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State the course requirement that must be met before any episode is classified under F31.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
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Explain why a documented manic episode from several years ago still matters when the current episode is purely depressive.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
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Describe what distinguishes a mixed episode (F31.6) from mania rapidly followed by depression as two separate episodes.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
These self-checks are a personal study aid only, visible to you on this page for this visit — they are not stored and do not affect your mastery dimensions.
Rapid revision card
F31: F31 requires a documented course of at least two episodes with at least one manic, hypomanic, or mixed; the current episode's type and severity then sets the fourth character.
Decisive boundary cues:
- A manic, hypomanic, or mixed episode documented at any point in the person's history -> weighs toward F31, whatever the current episode's polarity.
- Only ever depressive episodes, however many -> weighs toward F33, not F31.
- Only one episode ever, of either pole -> weighs toward F30 (elevated) or F32 (depressive), not F31, until a second episode occurs.
Duration/course: Episodes are usually separated by periods of substantially normal mood; the interval varies widely between individuals.
Nearest alternatives: F30, F33, F34
Common mistake: Classifying purely from the current episode's polarity and severity without checking the person's full episode history for a prior elevated-pole episode.
Retrieval prompt: Has an elevated-pole episode ever been documented for this person, at any point — not just in the current presentation?
(or use your browser's print function) Open full-page printable revision view →
Related glossary terms
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Mania
A state of abnormally and persistently elevated, expansive, or irritable mood accompanied by increased activity or energy, sufficient to cause marked functional impairment, require hospitalisation, or involve psychotic features. The most severe point on the elevated-mood gradient, above hypomania.
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Hypomania
A milder, sustained elevation of mood and increased activity that is a clear change from a person's usual baseline, but without the marked functional impairment, need for hospitalisation, or psychotic features that would make it mania.
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Mixed affective episode
An episode in which manic and depressive symptoms occur together or alternate very rapidly within the same episode, rather than one pole cleanly followed by the other. Classified as F31.6 when it occurs within an already-established bipolar course, or F38.0 when it is a first-ever episode with no such course yet documented.
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Mood-congruent (psychotic features)
Delusions or hallucinations whose content fits the prevailing mood — for example, grandiose delusions during mania, or delusions of guilt, nihilism, or hypochondriasis during severe depression. Contrasted with mood-incongruent features, whose content does not fit the mood and which raise consideration of an independent psychotic illness.
Source basis
WHO ICD-10 international classification structure and code/title (ICD-10 Browser, 2019 English release).
Original educational synthesis, informed by general published clinical-education understanding of ICD-10 F30-F39; no verbatim CDDG or DCR text is reproduced. See Sources and Method for the full policy.
Last reviewed: 2026-09-16. Full policy: Sources and Method.
Educational resource only. This page and its cases teach ICD-10 classification reasoning using fictional scenarios. It does not diagnose real people and should not be used to assess yourself or anyone else. If you or someone you know may be experiencing a mood episode, or is at risk of harming themselves, please seek prompt professional evaluation.