To diagnose bipolar disorder, doctors rely on a set of criteria published in The Diagnostic and Statistical Manual of Mental Disorders, commonly known as the DSM-5. This manual specifies three primary subtypes of bipolar disorder: bipolar I disorder, bipolar II disorder and cyclothymic disorder as well as several other forms of the illness.

Marchand says that there are distinct differences between each type of bipolar disorder.

“To have bipolar I, a person must have experienced at least one severe episode of elevated mood that meets diagnostic criteria of a manic episode at some time in their life,” says Dr. Marchand.  “Unfortunately, most individuals have multiple manic and depressive episodes as well as hypomanic episodes.”

Bipolar II is different than bipolar I in that manic episodes are not as extreme. “To be diagnosed as bipolar II, a person must have one or more occurrences of major depression and at least one episode of hypomania.  Most people experience multiple episodes of depression and hypomania,” says Marchand.

Yet another type of bipolar disorder is cyclothymia. “To be diagnosed with cyclothymia, a person must have experiences of both depressive episodes and mood elevations over at least two years,” says Marchand. ”This is a less extreme form of the illness and none of the episodes can meet criteria for major depression or hypomania.”

If you are concerned that someone you love is suffering from bipolar disorder, there are a number of things that you should look for. Dr. Marchand explains that this begins with suicidal thoughts.

“The most concerning symptom of bipolar depression is suicidal thinking,” says Dr. Marchand. “This is a medical emergency and requires immediate action.”