ICD-10 Code F31.81: Bipolar II Disorder Reference Guide

Key Takeaways

ICD-10 Code F31.81 is a billable diagnosis code for Bipolar II Disorder, valid for 2026 claims submissions.

F31.81 requires documentation of at least one hypomanic episode and at least one major depressive episode with no history of full manic episodes.

Do not default to F31.9 (bipolar disorder, unspecified) when F31.81 applies; specificity reduces claim denials and audit risk.

Pabau’s mental health EMR supports structured clinical documentation workflows that help practices capture the episode history required for F31.81.

Bipolar II disorder is one of the most commonly miscoded mood diagnoses in mental health billing. Clinicians frequently default to F31.9 (bipolar disorder, unspecified) or confuse F31.81 with Bipolar I codes, triggering denials and creating audit exposure. With payers increasingly scrutinising mood and anxiety spectrum diagnosis codes, accurate use of ICD-10 Code F31.81 matters more than ever for practice revenue and compliance. This reference covers code structure, documentation requirements, DSM-5 alignment, related codes, and billing guidance for mental health clinicians and coders.

ICD-10 Code F31.81: Definition and Code Structure

ICD-10 Code F31.81 is the designated billable code for Bipolar II Disorder within the ICD-10-CM classification system. It falls under Chapter 5 (F01-F99), Mental, Behavioural and Neurodevelopmental Disorders, within the subchapter F30-F39, Mood [Affective] Disorders, and more specifically within the F31 Bipolar Disorder category. According to the CDC/NCHS ICD-10-CM official tool, this code is valid and billable for the 2026 code year.

The official inclusion term for this code is “Bipolar disorder, type 2.” That distinction matters for coders: the code captures a specific clinical presentation rather than a broad diagnostic umbrella. Practices using a robust mental health EMR can configure documentation templates to prompt clinicians for the episode history that distinguishes F31.81 from adjacent codes in the F31 family.

Code Hierarchy at a Glance

One practical note: F31.8 (Other Bipolar Disorders) is the parent subcategory for F31.81 but is itself non-billable. Coders must always report to the highest level of specificity. When the clinical record supports Bipolar II disorder, F31.81 is the correct and only appropriate code.

Clinical Description: What Bipolar II Disorder Involves

Bipolar II disorder is characterised by a pattern of hypomanic and major depressive episodes, without a history of full manic episodes. This clinical distinction separates it from Bipolar I disorder (F31.1x), where full manic episodes are present. Because the hypomanic phase in Bipolar II is less severe than full mania, the condition is frequently missed or misclassified on initial presentation, often as unipolar depression.

For coding purposes, what counts is not the severity of current symptoms but whether the documented clinical history supports the diagnostic picture. A diagnosis of neurodevelopmental or mood spectrum conditions requires the clinician’s record to reflect the episode history, not just the presenting complaint. For F31.81 specifically, the record should capture both the hypomanic episode(s) and at least one major depressive episode.

Key Clinical Features for Documentation

• Hypomanic episode: Elevated or irritable mood and increased activity lasting at least 4 consecutive days, clearly different from usual behaviour but not severe enough to cause marked impairment or require hospitalisation.
• Major depressive episode: At least five depressive symptoms present most of the day, nearly every day, for at least two weeks, including depressed mood or loss of interest.
• No history of full manic episodes: If a full manic episode ever occurred, the diagnosis shifts to Bipolar I (F31.1x series), and F31.81 becomes incorrect.
• Not attributable to substance use or medical condition: The mood episodes must not be better explained by another condition or substance effect.

Mental health practices using psychiatry EMR software with structured intake templates can systematically capture episode history at assessment, reducing the risk of coding errors at claims submission.

Billable Status and Chart Section for F31.81

F31.81 is a fully billable, specific ICD-10-CM code. It can be used as a principal or secondary diagnosis on claims submitted to Medicare, Medicaid, and commercial payers for the 2026 code year. No additional specificity extensions are required; the code itself represents the complete diagnostic statement for Bipolar II disorder.

Practices should route claims through a claims management software system that validates code-level specificity before submission. This prevents defaulting to unspecified codes and reduces denials from payers who flag under-coded mood disorder claims.

Billing Status Summary

Documentation Requirements for ICD-10 Code F31.81

Claim adjudication for F31.81 depends on what the clinical record demonstrates, not just the diagnostic label. Payers expect documentation that justifies the specificity of this code over unspecified alternatives. The following elements should appear in the medical record to support F31.81 use.

• Episode history: Clear documentation of at least one hypomanic episode and at least one major depressive episode, with dates and symptom descriptions where possible.
• Absence of full mania: An explicit note that the patient has no history of full manic episodes, which distinguishes F31.81 from Bipolar I codes.
• Diagnostic basis: The clinical rationale connecting the documented symptom history to the Bipolar II diagnosis, often referencing DSM-5 criteria alignment.
• Longitudinal continuity: For established patients, progress notes should reference the ongoing diagnosis rather than re-establishing it from scratch at each visit.
• Co-occurring conditions: If anxiety, substance use, or other comorbidities are present, those require separate codes documented with equal specificity.

Practices using digital intake forms can build structured psychiatric history questionnaires that capture mood episode timelines at first contact, making documentation of episode history a systematic part of onboarding rather than a retrospective documentation task.

DSM-5 Alignment

The DSM-5 diagnosis of Bipolar II disorder maps directly to ICD-10 Code F31.81, per the APA-WHO coding alignment framework used across US clinical practice. According to the CMS ICD-10 codes guidance, clinicians should use the diagnostic criteria from DSM-5 to establish the clinical diagnosis before selecting the ICD-10-CM code for billing purposes.

The DSM-5 specifies additional dimensional descriptors for bipolar II disorder, including current episode type (hypomanic or depressed), severity, and presence of mixed features. These specifiers inform treatment planning but do not create separate ICD-10-CM codes at the F31.81 level. The code itself captures the diagnosis; narrative clinical notes capture the specifiers. Using a structured psychiatric evaluation template helps ensure specifier documentation is captured consistently.

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Related Codes and ICD-10 Code F31.81 Comparisons

Selecting F31.81 correctly requires understanding where it sits relative to adjacent codes. Two comparison points generate the most confusion in practice: F31.9 (unspecified) and the F31.1x Bipolar I series. Each represents a meaningfully different clinical and billing situation.

F31.81 vs. F31.9: Bipolar Disorder, Unspecified

F31.9 is a non-specific code indicating that the type of bipolar disorder has not been established. It is appropriate only when the clinical picture is genuinely unclear, such as during the initial evaluation period before a definitive diagnosis can be made. Once Bipolar II disorder is confirmed, F31.81 should replace F31.9 in all subsequent encounters.

Continued use of F31.9 after a Bipolar II diagnosis is established is a coding error. It reduces clinical specificity, may trigger medical necessity reviews, and can affect reimbursement for ongoing psychiatric services. The transition from F31.9 to F31.81 should be documented in the clinical record when the diagnosis is confirmed.

F31.81 vs. F31.1x: Bipolar I Disorder

Bipolar I disorder codes (F31.1x through F31.78) capture presentations where at least one full manic episode has occurred. The distinction hinges on manic vs. hypomanic episodes: a full manic episode involves more severe symptom intensity, lasts at least 7 days (or requires hospitalisation), and causes marked social or occupational impairment. Hypomania is present in Bipolar II but does not meet this threshold.

Coders must rely on the clinician’s explicit diagnostic statement rather than inferring from symptom descriptions. The clinical note should state “Bipolar II disorder” (mapping to F31.81) or “Bipolar I disorder” with the relevant episode specifier (mapping to the F31.1x family). When documentation is ambiguous, query the provider before assigning a code.

F31 Family Reference Table

The distinction between F34.0 (Cyclothymia) and F31.81 is also worth noting. Cyclothymia involves numerous hypomanic and depressive symptoms that do not meet full episode criteria. When episodes fully meet DSM-5 thresholds for Bipolar II, F31.81 applies. Accurate electronic client records that track episode history longitudinally help clinicians and coders identify which code applies as the diagnosis evolves.

Co-occurring Diagnoses and Secondary Code Guidance

Bipolar II disorder frequently presents alongside other conditions. Anxiety disorders, PTSD, substance use disorders, and ADHD all have elevated co-occurrence rates with bipolar spectrum diagnoses. Each co-occurring condition that is actively managed and documented should carry its own ICD-10-CM code on the claim.

• Anxiety disorders: Common co-occurring conditions include Generalised Anxiety Disorder (F41.1), Panic Disorder (F41.0), and Social Anxiety Disorder (F40.10). Code these separately when they represent distinct, documented clinical conditions being addressed in treatment.
• Major depressive episodes in context: Do not add a separate F32.x or F33.x code when the depressive episode is part of the Bipolar II pattern. The F31.81 code already captures that presentation.
• Substance use disorders: F10-F19 codes for alcohol and substance use disorders may be reported alongside F31.81 when both conditions are present and being managed.
• ADHD: F90.x codes for attention-deficit disorders are appropriate secondary codes when both diagnoses are documented and clinically relevant to the encounter.

Coders should follow the sequencing guidance in the CMS ICD-10-CM Official Guidelines: the condition chiefly responsible for the encounter is listed first, with additional codes listed as secondary. For most outpatient mental health visits focused on bipolar management, F31.81 will be the principal diagnosis. Reviewing how your practice handles complex mental health provider workflows can identify where co-morbidity documentation gaps are most likely to occur.

ICD-9 Crosswalk and Historical Context

The approximate ICD-9-CM equivalent of F31.81 is 296.89 (Other bipolar disorders). This crosswalk is relevant for practices reviewing historical records, processing late claims for periods before the ICD-10 transition, or conducting longitudinal data analyses across the 2015 changeover. The mapping is approximate rather than exact; the ICD-10-CM code system introduced greater diagnostic specificity that does not always have a clean one-to-one predecessor in ICD-9.

For practices needing to validate crosswalk accuracy or run code conversion queries, the ResDAC ICD codes in Medicare files resource provides guidance on how ICD codes are handled in Medicare claims data across the transition period. The WHO ICD classification framework also provides context for how the F31 category was restructured between ICD-10 and ICD-11, relevant for practices beginning to plan for ICD-11 adoption.

For coding reference and lookup needs, the AAPC Codify ICD-10-CM lookup provides searchable access to F31.81 and related codes with coding notes and crosswalk data. The ICD List tool also provides free ICD-10-CM reference with DRG grouper data useful for inpatient billing contexts.

Billing Guidance and Common Denial Patterns

Claim denials involving F31.81 most commonly fall into three categories: lack of medical necessity documentation, under-specificity (defaulting to F31.9 when F31.81 is supported), and bundling errors when co-occurring diagnoses are not coded separately.

Medical necessity for psychiatric services billed with F31.81 generally requires documentation showing the clinical rationale for the service provided, the treatment modality used, and the patient’s response or current status. For ongoing medication management visits, progress notes should reflect the current phase of the disorder, any medication adjustments, and the clinical reasoning behind the plan.

Telehealth Considerations

F31.81 is eligible for use on telehealth claims under current Medicare and most commercial payer rules for mental health services. Telehealth billing for psychiatric diagnoses requires the same documentation standards as in-person visits. The place of service code and any applicable telehealth modifiers vary by payer; practices should verify current payer-specific policies rather than assuming uniform telehealth billing rules across all insurers.

Practices managing telehealth workflows benefit from using telehealth software that maintains a consistent documentation structure across virtual and in-person encounters, reducing the risk of documentation gaps that trigger denials on mental health claims.

Expert Picks

Expert Picks

Need a structured tool for psychiatric assessments? Psychiatric Evaluation Template provides a step-by-step framework for comprehensive mental health assessments that capture the episode history required for accurate bipolar disorder coding.

Looking for clinical documentation tools built for mental health? Mental Health EMR covers how Pabau supports psychiatric and therapy practices with structured clinical notes, digital forms, and billing workflows.

Want to understand how claims management works for mental health practices? Claims Management Software outlines how Pabau’s billing tools help practices reduce denials and improve code-level accuracy before submission.

Conclusion

Mood disorder coding errors are rarely random. Most F31.81 claim problems trace back to one of two root causes: a clinician’s documentation that does not capture the episode history required to justify the code, or a coder defaulting to unspecified codes because the clinical record is ambiguous. Both are preventable with the right workflows in place.

Pabau’s mental health EMR supports the structured documentation that accurate F31.81 coding requires, from episode history intake forms to longitudinal clinical records that travel with the patient across encounters. If your practice is ready to reduce coding errors and streamline psychiatric billing, book a demo to see how Pabau handles mental health documentation and claims workflows end to end.

Frequently Asked Questions