What is a defining feature of Bipolar 1 disorder?

Bipolar I disorder is distinctly defined by the presence of at least one manic episode, which must last for a minimum of seven days, or by manic symptoms that are so severe that immediate hospital care is necessary. Additionally, while a depressive episode is not required for a diagnosis of Bipolar I disorder, having at least one depressive episode often accompanies the manic phase. This combination of manic and depressive episodes is what distinguishes Bipolar I from other mood disorders and subsets of bipolar disorder, such as Bipolar II, which requires at least one major depressive episode but does not involve a full manic episode.

The other options do not correctly encapsulate the requirements for diagnosing Bipolar I disorder. The focus on manic episodes alone or depressive episodes alone fails to recognize the essential component of the manic phase that defines Bipolar I disorder. Similarly, the notion of daily mood changes does not specifically address the structured episodes of mania and depression that characterize Bipolar I, as mood fluctuations can occur in various contexts without fitting the rigorous criteria of bipolar disorders.