Unipolar depression (F32.x for a single episode, F33.x for recurrent) involves depressive episodes only; bipolar disorder (the F31 codes) requires a history of at least one manic or hypomanic episode. Missing a bipolar diagnosis risks antidepressant monotherapy without mood stabilization, so screen for past hypomania or mania before coding depression.
Quick Comparison: Bipolar vs Unipolar Depression
| Attribute | Bipolar (F31.x) | Unipolar (F32/F33) |
|---|---|---|
| Required history | At least one manic episode (bipolar I) or hypomanic episode (bipolar II) | Depressive episodes only; no lifetime (hypo)mania |
| Episode types | Depressive, manic, hypomanic, and mixed episodes over the course | Depressive episodes only, single or recurrent |
| Treatment implication | Mood stabilization is foundational; antidepressant monotherapy is risky | Antidepressant therapy is a standard first-line option |
| ICD-10 code | F31.x family (for example F31.30 for a current depressed episode) | F32.x (single episode) or F33.x (recurrent) |
The one-line rule: depressive episodes alone point to unipolar depression (F32/F33). A single lifetime manic or hypomanic episode moves the diagnosis into the bipolar spectrum and the F31 family, even when the client is currently depressed.
The Clinical Stakes
At the moment a client sits in front of you low, withdrawn, and hopeless, bipolar depression and unipolar depression can look identical. A depressive episode is a depressive episode; the cross-sectional presentation does not tell you which illness you are looking at.
The differentiator is longitudinal: a history of at least one manic or hypomanic episode. That history is what separates bipolar disorder from unipolar major depression, and it is frequently invisible unless you go looking for it. Clients present during depressive episodes far more often than manic ones, and hypomania in particular is often experienced as a good stretch (more productive, more social, needing less sleep) rather than as a symptom to report.
The antidepressant-monotherapy risk: treating bipolar depression with an antidepressant alone, without a mood stabilizer, can destabilize the illness. Possible consequences include a switch into mania or hypomania, induction of rapid cycling, or precipitation of a mixed state. This is the concrete harm that a missed bipolar diagnosis can produce, and it is why the differential is not just an academic distinction.
Coding a depressive presentation as unipolar (F32 or F33) when the client actually has bipolar disorder does more than misclassify the diagnosis. It frames the treatment plan around the wrong illness and points toward exactly the monotherapy pattern that carries risk.
How to Screen Before Coding
Before assigning a depression code, actively screen for a lifetime history of mania or hypomania. Depression that presents today may be the depressive pole of a bipolar illness.
Ask directly about past periods of:
- Elevated, expansive, or unusually irritable mood that was a distinct change from baseline
- Decreased need for sleep (feeling rested after very little sleep, not just insomnia)
- Increased energy or goal-directed activity, racing thoughts, or rapid speech
- Impulsive or high-risk behavior (spending, sexual activity, business or travel decisions)
- Periods others noticed as out of character, even if the client did not see them as a problem
Consider a validated screening instrument for mood elevation as a structured aid, and corroborate with collateral history where appropriate, since clients often underreport hypomania. Duration and functional impact help distinguish mania (at least a week, or any duration requiring hospitalization) from hypomania (at least four days, clear change in functioning but not severe impairment).
Practical takeaway: a negative screen supports a unipolar code (F32/F33); a positive screen for even one past (hypo)manic episode moves you to the bipolar F31 family. Document the screening either way.
How to Code Each
Unipolar depression is coded in the F32 and F33 families. Use F32.x for a single major depressive episode and F33.x for recurrent major depressive disorder. Neither family carries any history of mania or hypomania.
| Code | Description | Notes |
|---|---|---|
| F32.0 | Major depressive disorder, single episode, mild | Single depressive episode; no (hypo)mania history |
| F32.1 | Major depressive disorder, single episode, moderate | Single depressive episode, moderate severity |
| F32.2 | Major depressive disorder, single episode, severe without psychotic features | Single severe episode, no psychosis |
| F33.0 | Major depressive disorder, recurrent, mild | Two or more episodes; still no (hypo)mania history |
| F33.1 | Major depressive disorder, recurrent, moderate | Recurrent depression, moderate severity |
Bipolar depression (a current depressive episode within bipolar I disorder) is coded under F31, not F32 or F33. The F31.3x, F31.4, and F31.5 codes specify a current depressed episode and its severity.
| Code | Description | Notes |
|---|---|---|
| F31.30 | Bipolar disorder, current episode depressed, mild or moderate severity, unspecified | Common code for a bipolar depressive episode without further severity detail |
| F31.31 | Bipolar disorder, current episode depressed, mild | Depressive episode within bipolar I, mild severity |
| F31.32 | Bipolar disorder, current episode depressed, moderate | Depressive episode within bipolar I, moderate severity |
| F31.4 | Bipolar disorder, current episode depressed, severe, without psychotic features | Severe bipolar depression, no psychosis |
| F31.5 | Bipolar disorder, current episode depressed, severe, with psychotic features | Severe bipolar depression with psychotic features |
Do not use F32 or F33 for a client with a bipolar history. Once a lifetime manic or hypomanic episode is established, a current depressive episode is coded in the F31 family. Using a unipolar code in that situation is a diagnostic error, not just a billing one, because it hides the bipolar illness from anyone reading the chart.
Documentation
Strong documentation for a depressive presentation should make the unipolar-versus-bipolar reasoning explicit:
Screening result: record that you screened for past mania and hypomania and what the client (and any collateral source) reported. A documented negative screen supports a unipolar code.
Episode history: note whether this is a single or recurrent episode for unipolar coding, and for bipolar, the presence and character of any prior (hypo)manic episodes.
Current severity: mild, moderate, or severe, and presence or absence of psychotic features, since these drive the fourth and fifth characters in both families.
Differential reasoning: a brief statement of why the presentation is unipolar (F32/F33) versus bipolar (F31), anchored to the presence or absence of lifetime (hypo)mania.
Treatment rationale: if bipolar, document that mood stabilization is being addressed and note the reasoning around antidepressant use, given the destabilization risk.
Frequently Asked Questions
- How do you tell bipolar from depression?
- The differentiator is history, not the current presentation. Unipolar depression involves depressive episodes only. Bipolar disorder requires a history of at least one manic episode (bipolar I) or hypomanic episode (bipolar II). Since bipolar depression and unipolar depression can look identical when a client presents low, you have to ask about past periods of elevated, expansive, or irritable mood with increased energy, decreased need for sleep, and impulsive behavior. A single lifetime manic or hypomanic episode moves the diagnosis into the bipolar spectrum.
- What is the ICD-10 code for unipolar depression?
- Unipolar major depressive disorder is coded in the F32 and F33 families. Use an F32.x code for a single episode (for example F32.0 mild, F32.1 moderate, F32.2 severe without psychotic features) and an F33.x code for recurrent major depressive disorder. There is no manic or hypomanic history with these codes; the presence of such a history moves you out of F32/F33 entirely.
- What is the code for bipolar depression?
- A depressive episode occurring within bipolar I disorder is coded under F31, not F32 or F33. Use the F31.3x, F31.4, or F31.5 codes for a current depressed episode, for example F31.30 (bipolar disorder, current episode depressed, mild or moderate severity, unspecified). The F31 code communicates that this depression sits inside a bipolar illness, which is the clinically critical distinction.
- Why does the distinction matter?
- It changes treatment. Bipolar depression is generally treated with a mood stabilizer or other bipolar-appropriate agent, often with mood stabilization as the foundation. Prescribing an antidepressant as monotherapy to someone with bipolar disorder can destabilize the illness, potentially triggering a manic or hypomanic switch, rapid cycling, or mixed states. Coding depression as unipolar when it is actually bipolar can steer the treatment plan toward exactly that risk.
- Can bipolar disorder be misdiagnosed as depression?
- Yes, and it commonly is. Clients frequently seek help during a depressive episode rather than a manic or hypomanic one, and hypomania in particular is often not experienced as a problem, so it goes unreported unless you ask directly. This is why structured screening for past (hypo)mania before coding a depressive presentation is the standard of care, not an optional extra.
The line between unipolar depression and bipolar disorder is drawn by history, not by how the client looks today. Screen for past mania and hypomania before you code a depressive episode, use F32/F33 only when that history is absent, and move to the F31 family the moment a single (hypo)manic episode is on the record.