ICD-10 Code for Bipolar II Disorder
The ICD-10 code for Bipolar II disorder is F31.81. 1
Understanding Bipolar Disorder Classification in ICD-10
The ICD-10 classification system uses F-codes (F30-F31) to categorize bipolar and related disorders 1:
- F30-31: Manic episode or bipolar affective disorder 1
- F31.81: Specifically designates Bipolar II disorder 1
- F32-33: Depressive episode and recurrent depressive disorder (used for unipolar depression, not bipolar) 1
Diagnostic Criteria Context
Bipolar II disorder requires at least one major depressive episode and at least one hypomanic episode (lasting at least 4 days), with no history of full manic or mixed episodes. 1, 2
Key Distinguishing Features from Bipolar I:
- Bipolar I disorder involves full manic episodes (7+ days or requiring hospitalization), coded differently in ICD-10 1
- Hypomania in Bipolar II does not cause marked impairment or require hospitalization, unlike mania 1, 2
- The presence of psychotic features indicates mania (Bipolar I), not hypomania 2
Clinical Importance of Accurate Coding
Bipolar II is frequently underdiagnosed or misdiagnosed as major depressive disorder (F32-33), leading to inappropriate antidepressant monotherapy that can worsen prognosis. 3
- Depressive episodes outnumber hypomanic episodes by approximately 39:1 in Bipolar II 3
- Patients typically present during depressive phases, making hypomania history easy to miss 2
- Antidepressant monotherapy without mood stabilizers risks mood destabilization and rapid cycling 4, 2
Common Coding Pitfalls to Avoid
- Do not use F32-33 codes (unipolar depression) when any history of hypomania exists, even if the patient presents with depression 1, 3
- Do not confuse with Bipolar NOS (F31.8 or F31.9), which is reserved for cases not meeting full criteria for Bipolar I or II 1
- Verify hypomania history through careful questioning about periods of elevated mood, decreased sleep need, increased goal-directed activity, and overactivity lasting at least 4 days 1, 2